First introduced in , [22] [23] [24] [25] [26] Phil Karn from Qualcomm is credited as the original designer. The purpose of a transit link is to route datagrams. They are used to free IP addresses from a scarce IP address space or to reduce the management of assigning IP and configuration of interfaces. When a link is unnumbered, a router-id is used, a single IP address borrowed from a defined normally a loopback interface.

The same router-id can be used on multiple interfaces. One of the disadvantages of unnumbered interfaces is that it is harder to do remote testing and management. In the s, it became apparent that the pool of available IPv4 addresses was depleting at a rate that was not initially anticipated in the original design of the network. In addition, high-speed Internet access was based on always-on devices. The threat of exhaustion motivated the introduction of a number of remedial technologies, such as:.

By the mids, network address translation NAT was used pervasively in network access provider systems, along with strict usage-based allocation policies at the regional and local Internet registries. The primary address pool of the Internet, maintained by IANA, was exhausted on 3 February , when the last five blocks were allocated to the five RIRs.

The long-term solution to address exhaustion was the specification of a new version of the Internet Protocol, IPv6. However, IPv4 is not directly interoperable with IPv6, so that IPv4-only hosts cannot directly communicate with IPv6-only hosts. With the phase-out of the 6bone experimental network starting in , permanent formal deployment of IPv6 commenced in An IP packet consists of a header section and a data section. An IP packet has no data checksum or any other footer after the data section.

Typically the link layer encapsulates IP packets in frames with a CRC footer that detects most errors, many transport-layer protocols carried by IP also have their own error checking.

The IPv4 packet header consists of 14 fields, of which 13 are required. The 14th field is optional and aptly named: options. The fields in the header are packed with the most significant byte first big endian , and for the diagram and discussion, the most significant bits are considered to come first MSB 0 bit numbering. The most significant bit is numbered 0, so the version field is actually found in the four most significant bits of the first byte, for example.

The packet payload is not included in the checksum. Its contents are interpreted based on the value of the Protocol header field. List of IP protocol numbers contains a complete list of payload protocol types.

Some of the common payload protocols include:. The Internet Protocol enables traffic between networks. The design accommodates networks of diverse physical nature; it is independent of the underlying transmission technology used in the link layer. Networks with different hardware usually vary not only in transmission speed, but also in the maximum transmission unit MTU. When one network wants to transmit datagrams to a network with a smaller MTU, it may fragment its datagrams.

In IPv4, this function was placed at the Internet Layer and is performed in IPv4 routers limiting exposure to these issues by hosts. In contrast, IPv6 , the next generation of the Internet Protocol, does not allow routers to perform fragmentation; hosts must perform Path MTU Discovery before sending datagrams.

When a router receives a packet, it examines the destination address and determines the outgoing interface to use and that interface's MTU. If the packet size is bigger than the MTU, and the Do not Fragment DF bit in the packet's header is set to 0, then the router may fragment the packet. The router divides the packet into fragments. The maximum size of each fragment is the outgoing MTU minus the IP header size 20 bytes minimum; 60 bytes maximum.

The router puts each fragment into its own packet, each fragment packet having the following changes:. It is possible that a packet is fragmented at one router, and that the fragments are further fragmented at another router. For example, a packet of 4, bytes, including a 20 bytes IP header is fragmented to two packets on a link with an MTU of 2, bytes:.

When forwarded to a link with an MTU of 1, bytes, each fragment is fragmented into two fragments:. Also in this case, the More Fragments bit remains 1 for all the fragments that came with 1 in them and for the last fragment that arrives, it works as usual, that is the MF bit is set to 0 only in the last one. And of course, the Identification field continues to have the same value in all re-fragmented fragments.

This way, even if fragments are re-fragmented, the receiver knows they have initially all started from the same packet.

A receiver knows that a packet is a fragment, if at least one of the following conditions is true:. The receiver identifies matching fragments using the source and destination addresses, the protocol ID, and the identification field. The receiver reassembles the data from fragments with the same ID using both the fragment offset and the more fragments flag.

When the receiver receives the last fragment, which has the more fragments flag set to 0, it can calculate the size of the original data payload, by multiplying the last fragment's offset by eight and adding the last fragment's data size. When the receiver has all fragments, they can be reassembled in the correct sequence according to the offsets to form the original datagram. IP addresses are not tied in any permanent manner to networking hardware and, indeed, in modern operating systems , a network interface can have multiple IP addresses.

In order to properly deliver an IP packet to the destination host on a link, hosts and routers need additional mechanisms to make an association between the hardware address [c] of network interfaces and IP addresses. The Address Resolution Protocol ARP performs this IP-address-to-hardware-address translation for IPv4.

In addition, the reverse correlation is often necessary. For example, unless an address is preconfigured by an administrator, when an IP host is booted or connected to a network it needs to determine its IP address.

Protocols for such reverse correlations include Dynamic Host Configuration Protocol DHCP , Bootstrap Protocol BOOTP and, infrequently, reverse ARP. From Wikipedia, the free encyclopedia. Redirected from IPv4. Fourth version of the Internet Protocol. Main article: Localhost. See also: IPv4 subnetting reference. Main article: Domain Name System. Main article: IPv4 address exhaustion. Main article: IP fragmentation. Retrieved IPv4 Market Group.

Archived from the original PDF on June 16, Cotton; L. Vegoda; B. Haberman April Bonica ed. Special-Purpose IP Address Registries. doi : ISSN BCP RFC Best Common Practice. Obsoletes RFC , , and Updated by RFC Rekhter; B. Moskowitz; D. Karrenberg; G. de Groot; E. Lear February Address Allocation for Private Internets. Network Working Group. BCP 5. Obsoletes RFC and The bytecode files are versioned and there is a strict version check, so bytecode files generated in one version of GCC do not work with an older or newer version of GCC.

Link-time optimization does not work well with generation of debugging information on systems other than those using a combination of ELF and DWARF. If you specify the optional n , the optimization and code generation done at link time is executed in parallel using n parallel jobs by utilizing an installed make program. The environment variable MAKE may be used to override the program used. This is useful when the Makefile calling GCC is already executing in parallel. This option likely only works if MAKE is GNU make.

Specify the partitioning algorithm used by the link-time optimizer. This option specifies the level of compression used for intermediate language written to LTO object files, and is only meaningful in conjunction with LTO mode -flto. GCC currently supports two LTO compression algorithms. For zstd, valid values are 0 no compression to 19 maximum compression , while zlib supports values from 0 to 9. Values outside this range are clamped to either minimum or maximum of the supported values.

If the option is not given, a default balanced compression setting is used. Enables the use of a linker plugin during link-time optimization. This option relies on plugin support in the linker, which is available in gold or in GNU ld 2. This option enables the extraction of object files with GIMPLE bytecode out of library archives.

This improves the quality of optimization by exposing more code to the link-time optimizer. This information specifies what symbols can be accessed externally by non-LTO object or during dynamic linking. Resulting code quality improvements on binaries and shared libraries that use hidden visibility are similar to -fwhole-program. See -flto for a description of the effect of this flag and how to use it.

This option is enabled by default when LTO support in GCC is enabled and GCC was configured for use with a linker supporting plugins GNU ld 2. Fat LTO objects are object files that contain both the intermediate language and the object code. This makes them usable for both LTO linking and normal linking. This option is effective only when compiling with -flto and is ignored at link time. It requires a linker with linker plugin support for basic functionality.

Additionally, nm , ar and ranlib need to support linker plugins to allow a full-featured build environment capable of building static libraries etc. GCC provides the gcc-ar , gcc-nm , gcc-ranlib wrappers to pass the right options to these tools. With non fat LTO makefiles need to be modified to use them.

Note that modern binutils provide plugin auto-load mechanism. After register allocation and post-register allocation instruction splitting, identify arithmetic instructions that compute processor flags similar to a comparison operation based on that arithmetic.

If possible, eliminate the explicit comparison operation. This pass only applies to certain targets that cannot explicitly represent the comparison operation before register allocation is complete. After register allocation and post-register allocation instruction splitting, perform a copy-propagation pass to try to reduce scheduling dependencies and occasionally eliminate the copy.

Profiles collected using an instrumented binary for multi-threaded programs may be inconsistent due to missed counter updates. When this option is specified, GCC uses heuristics to correct or smooth out such inconsistencies. By default, GCC emits an error message when an inconsistent profile is detected. With -fprofile-use all portions of programs not executed during train run are optimized agressively for size rather than speed.

In some cases it is not practical to train all possible hot paths in the program. For example, program may contain functions specific for a given hardware and trianing may not cover all hardware configurations program is run on. With -fprofile-partial-training profile feedback will be ignored for all functions not executed during the train run leading them to be optimized as if they were compiled without profile feedback.

This leads to better performance when train run is not representative but also leads to significantly bigger code. Enable profile feedback-directed optimizations, and the following optimizations, many of which are generally profitable only with profile feedback available:.

Before you can use this option, you must first generate profiling information. See Instrumentation Options , for information about the -fprofile-generate option.

By default, GCC emits an error message if the feedback profiles do not match the source code. Note this may result in poorly optimized code. Additionally, by default, GCC also emits a warning message if the feedback profiles do not exist see -Wmissing-profile. If path is specified, GCC looks at the path to find the profile feedback data files.

See -fprofile-dir. Enable sampling-based feedback-directed optimizations, and the following optimizations, many of which are generally profitable only with profile feedback available:. path is the name of a file containing AutoFDO profile information. If omitted, it defaults to fbdata. afdo in the current directory. You must also supply the unstripped binary for your program to this tool. The following options control compiler behavior regarding floating-point arithmetic. These options trade off between speed and correctness.

All must be specifically enabled. Do not store floating-point variables in registers, and inhibit other options that might change whether a floating-point value is taken from a register or memory. This option prevents undesirable excess precision on machines such as the where the floating registers of the keep more precision than a double is supposed to have. Similarly for the x86 architecture. For most programs, the excess precision does only good, but a few programs rely on the precise definition of IEEE floating point.

Use -ffloat-store for such programs, after modifying them to store all pertinent intermediate computations into variables. This option allows further control over excess precision on machines where floating-point operations occur in a format with more precision or range than the IEEE standard and interchange floating-point types. It may, however, yield faster code for programs that do not require the guarantees of these specifications.

Do not set errno after calling math functions that are executed with a single instruction, e. A program that relies on IEEE exceptions for math error handling may want to use this flag for speed while maintaining IEEE arithmetic compatibility. On Darwin systems, the math library never sets errno. There is therefore no reason for the compiler to consider the possibility that it might, and -fno-math-errno is the default.

Allow optimizations for floating-point arithmetic that a assume that arguments and results are valid and b may violate IEEE or ANSI standards. When used at link time, it may include libraries or startup files that change the default FPU control word or other similar optimizations. Enables -fno-signed-zeros , -fno-trapping-math , -fassociative-math and -freciprocal-math. Allow re-association of operands in series of floating-point operations.

May also reorder floating-point comparisons and thus may not be used when ordered comparisons are required. This option requires that both -fno-signed-zeros and -fno-trapping-math be in effect. For Fortran the option is automatically enabled when both -fno-signed-zeros and -fno-trapping-math are in effect. Allow the reciprocal of a value to be used instead of dividing by the value if this enables optimizations.

Note that this loses precision and increases the number of flops operating on the value. Allow optimizations for floating-point arithmetic that ignore the signedness of zero. Compile code assuming that floating-point operations cannot generate user-visible traps. These traps include division by zero, overflow, underflow, inexact result and invalid operation.

This option requires that -fno-signaling-nans be in effect. Disable transformations and optimizations that assume default floating-point rounding behavior. This is round-to-zero for all floating point to integer conversions, and round-to-nearest for all other arithmetic truncations. This option should be specified for programs that change the FP rounding mode dynamically, or that may be executed with a non-default rounding mode.

This option disables constant folding of floating-point expressions at compile time which may be affected by rounding mode and arithmetic transformations that are unsafe in the presence of sign-dependent rounding modes. This option is experimental and does not currently guarantee to disable all GCC optimizations that are affected by rounding mode.

Compile code assuming that IEEE signaling NaNs may generate user-visible traps during floating-point operations. Setting this option disables optimizations that may change the number of exceptions visible with signaling NaNs.

This option implies -ftrapping-math. This option is experimental and does not currently guarantee to disable all GCC optimizations that affect signaling NaN behavior. The default is -ffp-int-builtin-inexact , allowing the exception to be raised, unless C2X or a later C standard is selected. This option does nothing unless -ftrapping-math is in effect.

Treat floating-point constants as single precision instead of implicitly converting them to double-precision constants.

When enabled, this option states that a range reduction step is not needed when performing complex division.

The default is -fno-cx-limited-range , but is enabled by -ffast-math. Nevertheless, the option applies to all languages. Complex multiplication and division follow Fortran rules. The following options control optimizations that may improve performance, but are not enabled by any -O options. This section includes experimental options that may produce broken code. After running a program compiled with -fprofile-arcs see Instrumentation Options , you can compile it a second time using -fbranch-probabilities , to improve optimizations based on the number of times each branch was taken.

When a program compiled with -fprofile-arcs exits, it saves arc execution counts to a file called sourcename. gcda for each source file. The information in this data file is very dependent on the structure of the generated code, so you must use the same source code and the same optimization options for both compilations.

See details about the file naming in -fprofile-arcs. These can be used to improve optimization. Currently, they are only used in one place: in reorg. If combined with -fprofile-arcs , it adds code so that some data about values of expressions in the program is gathered. With -fbranch-probabilities , it reads back the data gathered from profiling values of expressions for usage in optimizations. Enabled by -fprofile-generate , -fprofile-use , and -fauto-profile.

Function reordering based on profile instrumentation collects first time of execution of a function and orders these functions in ascending order. If combined with -fprofile-arcs , this option instructs the compiler to add code to gather information about values of expressions. With -fbranch-probabilities , it reads back the data gathered and actually performs the optimizations based on them.

Currently the optimizations include specialization of division operations using the knowledge about the value of the denominator. Attempt to avoid false dependencies in scheduled code by making use of registers left over after register allocation.

This optimization most benefits processors with lots of registers. Performs a target dependent pass over the instruction stream to schedule instructions of same type together because target machine can execute them more efficiently if they are adjacent to each other in the instruction flow.

Perform tail duplication to enlarge superblock size. This transformation simplifies the control flow of the function allowing other optimizations to do a better job. Unroll loops whose number of iterations can be determined at compile time or upon entry to the loop. It also turns on complete loop peeling i. complete removal of loops with a small constant number of iterations. This option makes code larger, and may or may not make it run faster. Unroll all loops, even if their number of iterations is uncertain when the loop is entered.

This usually makes programs run more slowly. Peels loops for which there is enough information that they do not roll much from profile feedback or static analysis. complete removal of loops with small constant number of iterations. Enables the loop invariant motion pass in the RTL loop optimizer. Enabled at level -O1 and higher, except for -Og. Enables the loop store motion pass in the GIMPLE loop optimizer.

This moves invariant stores to after the end of the loop in exchange for carrying the stored value in a register across the iteration. Note for this option to have an effect -ftree-loop-im has to be enabled as well. Move branches with loop invariant conditions out of the loop, with duplicates of the loop on both branches modified according to result of the condition.

If a loop iterates over an array with a variable stride, create another version of the loop that assumes the stride is always one. This is particularly useful for assumed-shape arrays in Fortran where for example it allows better vectorization assuming contiguous accesses.

Place each function or data item into its own section in the output file if the target supports arbitrary sections. Use these options on systems where the linker can perform optimizations to improve locality of reference in the instruction space.

Most systems using the ELF object format have linkers with such optimizations. On AIX, the linker rearranges sections CSECTs based on the call graph. The performance impact varies. Together with a linker garbage collection linker --gc-sections option these options may lead to smaller statically-linked executables after stripping.

Only use these options when there are significant benefits from doing so. When you specify these options, the assembler and linker create larger object and executable files and are also slower. These options affect code generation. They prevent optimizations by the compiler and assembler using relative locations inside a translation unit since the locations are unknown until link time.

An example of such an optimization is relaxing calls to short call instructions. This transformation can help to reduce the number of GOT entries and GOT accesses on some targets. usually calculates the addresses of all three variables, but if you compile it with -fsection-anchors , it accesses the variables from a common anchor point instead.

Zero call-used registers at function return to increase program security by either mitigating Return-Oriented Programming ROP attacks or preventing information leakage through registers.

In some places, GCC uses various constants to control the amount of optimization that is done. For example, GCC does not inline functions that contain more than a certain number of instructions. You can control some of these constants on the command line using the --param option.

The names of specific parameters, and the meaning of the values, are tied to the internals of the compiler, and are subject to change without notice in future releases. In each case, the value is an integer. The following choices of name are recognized for all targets:. When branch is predicted to be taken with probability lower than this threshold in percent , then it is considered well predictable.

RTL if-conversion tries to remove conditional branches around a block and replace them with conditionally executed instructions. This parameter gives the maximum number of instructions in a block which should be considered for if-conversion. The compiler will also use other heuristics to decide whether if-conversion is likely to be profitable.

RTL if-conversion will try to remove conditional branches around a block and replace them with conditionally executed instructions.

These parameters give the maximum permissible cost for the sequence that would be generated by if-conversion depending on whether the branch is statically determined to be predictable or not. The maximum number of incoming edges to consider for cross-jumping. Increasing values mean more aggressive optimization, making the compilation time increase with probably small improvement in executable size.

The minimum number of instructions that must be matched at the end of two blocks before cross-jumping is performed on them. This value is ignored in the case where all instructions in the block being cross-jumped from are matched. The maximum code size expansion factor when copying basic blocks instead of jumping. The expansion is relative to a jump instruction. The maximum number of instructions to duplicate to a block that jumps to a computed goto.

Only computed jumps at the end of a basic blocks with no more than max-goto-duplication-insns are unfactored. The maximum number of instructions to consider when looking for an instruction to fill a delay slot. If more than this arbitrary number of instructions are searched, the time savings from filling the delay slot are minimal, so stop searching.

Increasing values mean more aggressive optimization, making the compilation time increase with probably small improvement in execution time. When trying to fill delay slots, the maximum number of instructions to consider when searching for a block with valid live register information.

Increasing this arbitrarily chosen value means more aggressive optimization, increasing the compilation time. This parameter should be removed when the delay slot code is rewritten to maintain the control-flow graph. The approximate maximum amount of memory in kB that can be allocated in order to perform the global common subexpression elimination optimization. If more memory than specified is required, the optimization is not done. If the ratio of expression insertions to deletions is larger than this value for any expression, then RTL PRE inserts or removes the expression and thus leaves partially redundant computations in the instruction stream.

The maximum number of pending dependencies scheduling allows before flushing the current state and starting over. Large functions with few branches or calls can create excessively large lists which needlessly consume memory and resources.

The maximum number of backtrack attempts the scheduler should make when modulo scheduling a loop. Larger values can exponentially increase compilation time. Maximal loop depth of a call considered by inline heuristics that tries to inline all functions called once. Several parameters control the tree inliner used in GCC. When you use -finline-functions included in -O3 , a lot of functions that would otherwise not be considered for inlining by the compiler are investigated.

To those functions, a different more restrictive limit compared to functions declared inline can be applied --param max-inline-insns-auto. This is bound applied to calls which are considered relevant with -finline-small-functions.

This is bound applied to calls which are optimized for size. Small growth may be desirable to anticipate optimization oppurtunities exposed by inlining. Number of instructions accounted by inliner for function overhead such as function prologue and epilogue. Extra time accounted by inliner for function overhead such as time needed to execute function prologue and epilogue.

The scale in percents applied to inline-insns-single , inline-insns-single-O2 , inline-insns-auto when inline heuristics hints that inlining is very profitable will enable later optimizations.

Same as --param uninlined-function-insns and --param uninlined-function-time but applied to function thunks. The limit specifying really large functions. For functions larger than this limit after inlining, inlining is constrained by --param large-function-growth. This parameter is useful primarily to avoid extreme compilation time caused by non-linear algorithms used by the back end.

Specifies maximal growth of large function caused by inlining in percents. For example, parameter value limits large function growth to 2. The limit specifying large translation unit. Growth caused by inlining of units larger than this limit is limited by --param inline-unit-growth. For small units this might be too tight. For example, consider a unit consisting of function A that is inline and B that just calls A three times.

For very large units consisting of small inlineable functions, however, the overall unit growth limit is needed to avoid exponential explosion of code size. Thus for smaller units, the size is increased to --param large-unit-insns before applying --param inline-unit-growth. Specifies maximal overall growth of the compilation unit caused by inlining. For example, parameter value 20 limits unit growth to 1. Cold functions either marked cold via an attribute or by profile feedback are not accounted into the unit size.

Specifies maximal overall growth of the compilation unit caused by interprocedural constant propagation. For example, parameter value 10 limits unit growth to 1. The limit specifying large stack frames. While inlining the algorithm is trying to not grow past this limit too much. Specifies maximal growth of large stack frames caused by inlining in percents.

For example, parameter value limits large stack frame growth to 11 times the original size. Specifies the maximum number of instructions an out-of-line copy of a self-recursive inline function can grow into by performing recursive inlining. For functions not declared inline, recursive inlining happens only when -finline-functions included in -O3 is enabled; --param max-inline-insns-recursive-auto applies instead.

For functions not declared inline, recursive inlining happens only when -finline-functions included in -O3 is enabled; --param max-inline-recursive-depth-auto applies instead. Recursive inlining is profitable only for function having deep recursion in average and can hurt for function having little recursion depth by increasing the prologue size or complexity of function body to other optimizers.

When profile feedback is available see -fprofile-generate the actual recursion depth can be guessed from the probability that function recurses via a given call expression. This parameter limits inlining only to call expressions whose probability exceeds the given threshold in percents. Specify growth that the early inliner can make. In effect it increases the amount of inlining for code having a large abstraction penalty.

Limit of iterations of the early inliner. This basically bounds the number of nested indirect calls the early inliner can resolve. Deeper chains are still handled by late inlining. This parameter ought to be bigger than --param modref-max-bases and --param modref-max-refs. Specifies the maximum depth of DFS walk used by modref escape analysis.

Setting to 0 disables the analysis completely. A parameter to control whether to use function internal id in profile database lookup. If the value is 0, the compiler uses an id that is based on function assembler name and filename, which makes old profile data more tolerant to source changes such as function reordering etc. The minimum number of iterations under which loops are not vectorized when -ftree-vectorize is used. The number of iterations after vectorization needs to be greater than the value specified by this option to allow vectorization.

Scaling factor in calculation of maximum distance an expression can be moved by GCSE optimizations. This is currently supported only in the code hoisting pass. The bigger the ratio, the more aggressive code hoisting is with simple expressions, i.

Specifying 0 disables hoisting of simple expressions. Cost, roughly measured as the cost of a single typical machine instruction, at which GCSE optimizations do not constrain the distance an expression can travel. The lesser the cost, the more aggressive code hoisting is. Specifying 0 allows all expressions to travel unrestricted distances. The depth of search in the dominator tree for expressions to hoist.

This is used to avoid quadratic behavior in hoisting algorithm. The value of 0 does not limit on the search, but may slow down compilation of huge functions.

The maximum amount of similar bbs to compare a bb with. This is used to avoid quadratic behavior in tree tail merging. The maximum amount of iterations of the pass over the function. This is used to limit compilation time in tree tail merging. The maximum number of store chains to track at the same time in the attempt to merge them into wider stores in the store merging pass. The maximum number of stores to track at the same time in the attemt to to merge them into wider stores in the store merging pass.

The maximum number of instructions that a loop may have to be unrolled. If a loop is unrolled, this parameter also determines how many times the loop code is unrolled. The maximum number of instructions biased by probabilities of their execution that a loop may have to be unrolled. The maximum number of instructions that a loop may have to be peeled.

If a loop is peeled, this parameter also determines how many times the loop code is peeled. When FDO profile information is available, min-loop-cond-split-prob specifies minimum threshold for probability of semi-invariant condition statement to trigger loop split. Bound on number of candidates for induction variables, below which all candidates are considered for each use in induction variable optimizations.

If there are more candidates than this, only the most relevant ones are considered to avoid quadratic time complexity. If the number of candidates in the set is smaller than this value, always try to remove unnecessary ivs from the set when adding a new one.

Maximum size in bytes of objects tracked bytewise by dead store elimination. Larger values may result in larger compilation times. Maximum number of queries into the alias oracle per store. Larger values result in larger compilation times and may result in more removed dead stores.

Bound on size of expressions used in the scalar evolutions analyzer. Large expressions slow the analyzer. Bound on the complexity of the expressions in the scalar evolutions analyzer. Complex expressions slow the analyzer.

Maximum number of arguments in a PHI supported by TREE if conversion unless the loop is marked with simd pragma. The maximum number of possible vector layouts such as permutations to consider when optimizing to-be-vectorized code.

The maximum number of run-time checks that can be performed when doing loop versioning for alignment in the vectorizer. The maximum number of run-time checks that can be performed when doing loop versioning for alias in the vectorizer. The maximum number of loop peels to enhance access alignment for vectorizer.

Value -1 means no limit. The maximum number of iterations of a loop the brute-force algorithm for analysis of the number of iterations of the loop tries to evaluate. Used in non-LTO mode. The number of most executed permilles, ranging from 0 to , of the profiled execution of the entire program to which the execution count of a basic block must be part of in order to be considered hot.

The default is , which means that a basic block is considered hot if its execution count contributes to the upper permilles, or Used in LTO mode.

The maximum number of loop iterations we predict statically. This is useful in cases where a function contains a single loop with known bound and another loop with unknown bound. The known number of iterations is predicted correctly, while the unknown number of iterations average to roughly This means that the loop without bounds appears artificially cold relative to the other one. Control the probability of the expression having the specified value.

This parameter takes a percentage i. Select fraction of the maximal frequency of executions of a basic block in a function to align the basic block. This value is used to limit superblock formation once the given percentage of executed instructions is covered. This limits unnecessary code size expansion.

The tracer-dynamic-coverage-feedback parameter is used only when profile feedback is available. The real profiles as opposed to statically estimated ones are much less balanced allowing the threshold to be larger value. Stop tail duplication once code growth has reached given percentage.

This is a rather artificial limit, as most of the duplicates are eliminated later in cross jumping, so it may be set to much higher values than is the desired code growth. Stop reverse growth when the reverse probability of best edge is less than this threshold in percent.

Similarly to tracer-dynamic-coverage two parameters are provided. tracer-min-branch-probability-feedback is used for compilation with profile feedback and tracer-min-branch-probability compilation without.

The value for compilation with profile feedback needs to be more conservative higher in order to make tracer effective.

Specify the size of the operating system provided stack guard as 2 raised to num bytes. Higher values may reduce the number of explicit probes, but a value larger than the operating system provided guard will leave code vulnerable to stack clash style attacks. Stack clash protection involves probing stack space as it is allocated. This param controls the maximum distance between probes into the stack as 2 raised to num bytes. GCC uses a garbage collector to manage its own memory allocation.

Tuning this may improve compilation speed; it has no effect on code generation. Setting this parameter and ggc-min-heapsize to zero causes a full collection to occur at every opportunity. This is extremely slow, but can be useful for debugging. Again, tuning this may improve compilation speed, and has no effect on code generation.

If GCC is not able to calculate RAM on a particular platform, the lower bound is used. Setting this parameter very large effectively disables garbage collection. Setting this parameter and ggc-min-expand to zero causes a full collection to occur at every opportunity. The maximum number of instruction reload should look backward for equivalent register. Increasing values mean more aggressive optimization, making the compilation time increase with probably slightly better performance.

The maximum number of memory locations cselib should take into account. The maximum number of instructions ready to be issued the scheduler should consider at any given time during the first scheduling pass.

Increasing values mean more thorough searches, making the compilation time increase with probably little benefit. The maximum number of blocks in a region to be considered for pipelining in the selective scheduler. The maximum number of insns in a region to be considered for pipelining in the selective scheduler.

The minimum probability in percents of reaching a source block for interblock speculative scheduling. The maximum number of iterations through CFG to extend regions. A value of 0 disables region extensions. The minimal probability of speculation success in percents , so that speculative insns are scheduled. The maximum size of the lookahead window of selective scheduling.

It is a depth of search for available instructions. The maximum number of times that an instruction is scheduled during selective scheduling. This is the limit on the number of iterations through which the instruction may be pipelined. The maximum number of best instructions in the ready list that are considered for renaming in the selective scheduler. The maximum size measured as number of RTLs that can be recorded in an expression in combiner for a pseudo register as last known value of that register.

This sets the maximum value of a shared integer constant. The minimum size of buffers i. arrays that receive stack smashing protection when -fstack-protector is used. Maximum number of statements allowed in a block that needs to be duplicated when threading jumps. The maximum number of paths to consider when searching for jump threading opportunities.

When arriving at a block, incoming edges are only considered if the number of paths to be searched so far multiplied by the number of incoming edges does not exhaust the specified maximum number of paths to consider.

Maximum number of fields in a structure treated in a field sensitive manner during pointer analysis. Estimate on average number of instructions that are executed before prefetch finishes. The distance prefetched ahead is proportional to this constant. Increasing this number may also lead to less streams being prefetched see simultaneous-prefetches. Whether the loop array prefetch pass should issue software prefetch hints for strides that are non-constant.

In some cases this may be beneficial, though the fact the stride is non-constant may make it hard to predict when there is clear benefit to issuing these hints. Set to 1 if the prefetch hints should be issued for non-constant strides. Set to 0 if prefetch hints should be issued only for strides that are known to be constant and below prefetch-minimum-stride. Complete checking of a package which contains a file README. You do need to ensure that the package is checked in a suitable locale if it contains non- ASCII characters.

Such packages are likely to fail some of the checks in a C locale, and R CMD check will warn if it spots the problem. You should be able to check any package in a UTF-8 locale if one is available. Beware that although a C locale is rarely used at a console, it may be the default if logging in remotely or for batch jobs. Often R CMD check will need to consult a CRAN repository to check details of uninstalled packages.

Next: Building binary packages , Previous: Checking packages , Up: Checking and building packages [ Contents ][ Index ]. gz files or in binary form. The source form can be installed on all platforms with suitable tools and is the usual form for Unix-like systems; the binary form is platform-specific, and is the more common distribution form for the Windows and macOS platforms.

Using R CMD build , the R package builder, one can build R package tarballs from their sources for example, for subsequent release. Prior to actually building the package in the standard gzipped tar file format, a few diagnostic checks and cleanups are performed. Run-time checks whether the package works correctly should be performed using R CMD check prior to invoking the final build procedure. To exclude files from being put into the package, one can specify a list of exclude patterns in file.

Rbuildignore in the top-level source directory. These patterns should be Perl-like regular expressions see the help for regexp in R for the precise details , one per line, to be matched case-insensitively against the file and directory names relative to the top-level package source directory.

In addition, directories from source control systems 54 or from eclipse 55 , directories with names check , chm , or ending. In addition, same-package tarballs from previous builds and their binary forms will be excluded from the top-level directory, as well as those files in the R , demo and man directories which are flagged by R CMD check as having invalid names.

Use R CMD build --help to obtain more information about the usage of the R package builder. To do so it installs the current package into a temporary library tree, but any dependent packages need to be installed in an available library tree see the Note: at the top of this section.

Similarly, if the. If there are any install-time or render-time macros, a. pdf version of the package manual will be built and installed in the build subdirectory. This allows CRAN or other repositories to display the manual even if they are unable to install the package. One of the checks that R CMD build runs is for empty source directories.

The --resave-data option allows saved images. rda and. RData files in the data directory to be optimized for size. It will also compress tabular files and convert. R files to saved images. Where a non-POSIX file system is in use which does not utilize execute permissions, some care is needed with permissions. This applies on Windows and to e. FAT-formatted drives and SMB-mounted file systems on other OSes. info returns. A particular issue is packages being built on Windows which are intended to contain executable scripts such as configure and cleanup : R CMD build ensures those two are recorded with execute permission.

Directory build of the package sources is reserved for use by R CMD build : it contains information which may not easily be created when the package is installed, including index information on the vignettes and, rarely, information on the help pages and perhaps a copy of the PDF reference manual see above.

Previous: Building package tarballs , Up: Checking and building packages [ Contents ][ Index ]. Binary packages are compressed copies of installed versions of packages. The format and filename are platform-specific; for example, a binary package for Windows is usually supplied as a. zip file, and for the macOS platform the default binary package file extension is.

R CMD INSTALL --build pkg where pkg is either the name of a source tarball in the usual. gz format or the location of the directory of the package source to be built. This operates by first installing the package and then packing the installed binaries into the appropriate binary package file for the particular platform.

By default, R CMD INSTALL --build will attempt to install the package into the default library tree for the local installation of R. This has two implications:. To prevent changes to the present working installation or to provide an install location with write access, create a suitably located directory with write access and use the -l option to build the package in the chosen location. The usage is then. where location is the chosen directory with write access.

The package will be installed as a subdirectory of location , and the package binary will be created in the current directory. Other options for R CMD INSTALL can be found using R CMD INSTALL --help , and platform-specific details for special cases are discussed in the platform-specific FAQs.

Note that this is intended for developers on other platforms who do not have access to Windows but wish to provide binaries for the Windows platform.

Next: Package namespaces , Previous: Checking and building packages , Up: Creating R packages [ Contents ][ Index ].

In addition to the help files in Rd format, R packages allow the inclusion of documents in arbitrary other formats. Pointers from package help indices to the installed documents are automatically created. To ensure that they can be accessed from a browser as an HTML index is provided , the file names should start with an ASCII letter and be comprised entirely of ASCII letters or digits or hyphen or underscore.

A special case is package vignettes. Sweave, provided by the R distribution, is the default engine. Other vignette engines besides Sweave are supported; see Non-Sweave vignettes. Package vignettes have their sources in subdirectory vignettes of the package sources. Sweave vignette sources are normally given the file extension.

Rnw or. Rtex , but for historical reasons extensions Snw and. Stex are also recognized. Sweave allows the integration of LaTeX documents: see the Sweave help page in R and the Sweave vignette in package utils for details on the source document format. Package vignettes are tested by R CMD check by executing all R code chunks they contain except those marked for non-evaluation, e. The R working directory for all vignette tests in R CMD check is a copy of the vignette source directory.

All other files needed to re-make the vignettes such as LaTeX style files, BibTeX input files and files for any figures not created by running the code in the vignette must be in the vignette source directory. By including the vignette outputs in the package sources it is not necessary that these can be re-built at install time, i.

By default R CMD build will run Sweave on all Sweave vignette source files in vignettes. If Makefile is found in the vignette source directory, then R CMD build will try to run make after the Sweave runs, otherwise texi2pdf is run on each.

tex file produced. All the usual caveats about including a Makefile apply. It must be portable no GNU extensions , use LF line endings and must work correctly with a parallel make : too many authors have written things like. Metadata lines can be placed in the source file, preferably in LaTeX comments in the preamble.

This index is linked from the HTML help index for the package. Do watch that PDFs are not too large — one in a CRAN package was 72MB! This is usually caused by the inclusion of overly detailed figures, which will not render well in PDF viewers. Sometimes it is much better to generate fairly high resolution bitmap PNG, JPEG figures and include those in the PDF document.

See the description of the. Rinstignore file for full details. Next: Non-Sweave vignettes , Previous: Writing package vignettes , Up: Writing package vignettes [ Contents ][ Index ]. Vignettes will in general include descriptive text, R input, R output and figures, LaTeX include files and bibliographic references. As any of these may contain non- ASCII characters, the handling of encodings can become very complicated.

The vignette source file should be written in ASCII or contain a declaration of the encoding see below. This applies even to comments within the source file, since vignette engines process comments to look for options and metadata lines. Sweave will produce a. tex file in the current encoding, or in UTF-8 if that is declared.

Non- ASCII encodings need to be declared to LaTeX via a line like. For files where this line is not needed e. chapters included within the body of a larger document, or non-Sweave vignettes , the encoding may be declared using a comment like. If no declaration is given in the vignette, it will be assumed to be in the encoding declared for the package.

If there is no encoding declared in either place, then it is an error to use non- ASCII characters in the vignette. Sweave will also parse and evaluate the R code in each chunk. One thing people often forget is that the R output may not be ASCII even for ASCII R sources, for many possible reasons. The final issue is the encoding of figures — this applies only to PDF figures and not PNG etc.

The PDF figures will contain declarations for their encoding, but the Sweave option pdf. encoding may need to be set appropriately: see the help for the pdf graphics device. That package did not have a declared encoding, and its vignette was in ASCII. However, the data it displays are read from a UTF-8 CSV file and will be assumed to be in the current encoding, so fortunes.

tex will be in UTF-8 in any locale. Had read. table been told the data were UTF-8, fortunes. Previous: Encodings and vignettes , Up: Writing package vignettes [ Contents ][ Index ]. For example knitr version 1. tex files from a variation on Sweave format, and. These engines replace the Sweave function with other functions to convert vignette source files into LaTeX files for processing into.

pdf , or directly into. pdf or. html files. The Stangle function is replaced with a function that extracts the R source from a vignette. R recognizes non-Sweave vignettes using filename extensions specified by the engine.

For example, the knitr package supports the extension. This specifies the name of a package and an engine to use in place of Sweave in processing the vignette. If more than one package is specified as a builder, they will be searched in the order given there. The utils package is always implicitly appended to the list of builder packages, but may be included earlier to change the search order.

The vignette engine can produce. tex ,. pdf , or. html files as output. If it produces. tex files, R will call texi2pdf to convert them to. pdf for display to the user unless there is a Makefile in the vignettes directory.

Package writers who would like to supply vignette engines need to register those engines in the package. onLoad function. For example, that function could make the call. The actual registration in knitr is more complicated, because it supports other input formats.

See the? tools::vignetteEngine help topic for details on engine registration. Next: Writing portable packages , Previous: Writing package vignettes , Up: Creating R packages [ Contents ][ Index ]. R has a namespace management system for code in packages. This system allows the package writer to specify which variables in the package should be exported to make them available to package users, and which variables should be imported from other packages.

The namespace for a package is specified by the NAMESPACE file in the top level package directory. This file contains namespace directives describing the imports and exports of the namespace. Additional directives register any shared objects to be loaded and any S3-style methods that are provided.

Note that although the file looks like R code and often has R-style comments it is not processed as R code. Only very simple conditional processing of if statements is implemented. Packages are loaded and attached to the search path by calling library or require. Only the exported variables are placed in the attached frame.

Loading a package that imports variables from other packages will cause these other packages to be loaded as well unless they have already been loaded , but they will not be placed on the search path by these implicit loads.

Thus code in the package can only depend on objects in its own namespace and its imports including the base namespace being visible Namespaces are sealed once they are loaded. Sealing means that imports and exports cannot be changed and that internal variable bindings cannot be changed.

Sealing allows a simpler implementation strategy for the namespace mechanism and allows code analysis and compilation tools to accurately identify the definition corresponding to a global variable reference in a function body. The namespace controls the search strategy for variables used by functions in the package.

If not found locally, R searches the package namespace first, then the imports, then the base namespace and then the normal search path so the base namespace precedes the normal search rather than being at the end of it. Next: Registering S3 methods , Previous: Package namespaces , Up: Package namespaces [ Contents ][ Index ]. Exports are specified using the export directive in the NAMESPACE file. A directive of the form.

specifies that the variables f and g are to be exported. fractions must be. For packages with many variables to export it may be more convenient to specify the names to export with a regular expression using exportPattern.

The directive. exports all variables that do not start with a period. However, such broad patterns are not recommended for production code: it is better to list all exports or use narrowly-defined groups.

This pattern applies to S4 classes. Beware of patterns which include names starting with a period: some of these are internal-only variables and should never be exported, e. Packages implicitly import the base namespace. Variables exported from other packages with namespaces need to be imported explicitly using the directives import and importFrom.

The import directive imports all exported variables from the specified package s. Thus the directives. specifies that all exported variables in the packages foo and bar are to be imported.

If only some of the exported variables from a package are needed, then they can be imported using importFrom. specifies that the exported variables f and g of the package foo are to be imported. Using importFrom selectively rather than import is good practice and recommended notably when importing from packages with more than a dozen exports and especially from those written by others so what they export can change in future.

To import every symbol from a package but for a few exceptions, pass the except argument to import. imports every symbol from foo except bar and baz. The value of except should evaluate to something coercible to a character vector, after substituting each symbol for its corresponding string.

It is possible to export variables from a namespace which it has imported from other namespaces: this has to be done explicitly and not via exportPattern. If a package only needs a few objects from another package it can use a fully qualified variable reference in the code instead of a formal import. A fully-qualified reference to the function f in package foo is of the form foo::f.

Evaluating foo::f will cause package foo to be loaded, but not attached, if it was not loaded already—this can be an advantage in delaying the loading of a rarely used package. Using the foo::f form will be necessary when a package needs to use a function of the same name from more than one namespace.

Using foof instead of foo::f allows access to unexported objects. This is generally not recommended, as the existence or semantics of unexported objects may be changed by the package author in routine maintenance.

Next: Load hooks , Previous: Specifying imports and exports , Up: Package namespaces [ Contents ][ Index ]. The standard method for S3-style UseMethod dispatching might fail to locate methods defined in a package that is imported but not attached to the search path. To ensure that these methods are available the packages defining the methods should ensure that the generics are imported and register the methods using S3method directives.

If a package defines a function print. foo intended to be used as a print method for class foo , then the directive. ensures that the method is registered and available for UseMethod dispatch, and the function print. foo does not need to be exported. Since the generic print is defined in base it does not need to be imported explicitly. It is possible to specify a third argument to S3method, the function to be used as the method, for example.

As from R 3. function gen. cls will get registered as an S3 method for class cls and generic gen from package pkg only when the namespace of pkg is loaded. Next: useDynLib , Previous: Registering S3 methods , Up: Package namespaces [ Contents ][ Index ]. There are a number of hooks called as packages are loaded, attached, detached, and unloaded.

See help ". onLoad" for more details. Since loading and attaching are distinct operations, separate hooks are provided for each. These hook functions are called. onLoad and. They both take arguments 63 libname and pkgname ; they should be defined in the namespace but not exported. Packages can use a. onDetach or. lib function provided the latter is exported from the namespace when detach is called on the package.

It is called with a single argument, the full path to the installed package. There is also a hook. onUnload and. onDetach should be defined in the namespace and not exported, but. lib does need to be exported. Packages are not likely to need. onAttach except perhaps for a start-up banner ; code to set options and load shared objects should be placed in a. onLoad function, or use made of the useDynLib directive described next.

These hooks are often used incorrectly. People forget to export. Compiled code should be loaded in. onLoad or via a useDynLb directive: see below and unloaded in. by pkgname::fun and that a package can be detached and re-attached whilst its namespace remains loaded. It is good practice for these functions to be quiet. Any messages should use packageStartupMessage so users include check scripts can suppress them if desired.

Next: An example , Previous: Load hooks , Up: Package namespaces [ Contents ][ Index ]. A NAMESPACE file can contain one or more useDynLib directives which allows shared objects that need to be loaded. registers the shared object foo 65 for loading with library.

Loading of registered object s occurs after the package code has been loaded and before running the load hook function. Packages that would only need a load hook function to load a shared object can use the useDynLib directive instead. The useDynLib directive also accepts the names of the native routines that are to be used in R via the.

Call ,. Fortran and. External interface functions. These are given as additional arguments to the directive, for example,. These can be used in the. External calls in place of the name of the routine and the PACKAGE argument. For instance, we can call the routine myRoutine from R with the code. There are at least two benefits to this approach.

Firstly, the symbol lookup is done just once for each symbol rather than each time the routine is invoked. Secondly, this removes any ambiguity in resolving symbols that might be present in more than one DLL. However, this approach is nowadays deprecated in favour of supplying registration information see below.

In some circumstances, there will already be an R variable in the package with the same name as a native symbol.

For example, we may have an R function in the package named myRoutine. In this case, it is necessary to map the native symbol to a different R variable name. This can be done in the useDynLib directive by using named arguments. It may be too costly to compute these for many routines when the package is loaded if many of these routines are not likely to be used.

In this case, one can still perform the symbol resolution correctly using the DLL, but do this each time the routine is called. Given a reference to the DLL as an R variable, say dll , we can call the routine myRoutine using the expression. This is the same computation as above where we resolve the symbol when the package is loaded. In order to use this dynamic approach e.

For example, if we wanted to assign the DLL reference for the DLL foo in the example above to the variable myDLL , we would use the following directive in the NAMESPACE file:. If the package has registration information see Registering native routines , then we can use that directly rather than specifying the list of symbols again in the useDynLib directive in the NAMESPACE file. Each routine in the registration information is specified by giving a name by which the routine is to be specified along with the address of the routine and any information about the number and type of the parameters.

Using the. registration argument of useDynLib , we can instruct the namespace mechanism to create R variables for these symbols. For example, suppose we have the following registration information for a DLL named myDLL :. Note that the names for the R variables are taken from the entry in the registration information and do not need to be the same as the name of the native routine.

This allows the creator of the registration information to map the native symbols to non-conflicting variable names in R, e. Using argument. fixes allows an automatic prefix to be added to the registered symbols, which can be useful when working with an existing package. For example, package KernSmooth has. NB : Using these arguments for a package which does not register native symbols merely slows down the package loading although many CRAN packages have done so.

Once symbols are registered, check that the corresponding R variables are not accidentally exported by a pattern in the NAMESPACE file. Next: Namespaces with S4 classes and methods , Previous: useDynLib , Up: Package namespaces [ Contents ][ Index ].

As an example consider two packages named foo and bar. The R code for package foo in file foo. Some C code defines a C function compiled into DLL foo with an appropriate extension. The NAMESPACE file for this package is. Calling library bar loads bar and attaches its exports to the search path.

Package foo is also loaded but not attached to the search path. A call to g produces. This is consistent with the definitions of c in the two settings: in bar the function c is defined to be equivalent to sum , but in foo the variable c refers to the standard function c in base. Previous: An example , Up: Package namespaces [ Contents ][ Index ].

Some additional steps are needed for packages which make use of formal S4-style classes and methods unless these are purely used internally. plus any classes and methods which are to be exported need to be declared in the NAMESPACE file. For example, the stats4 package has. All S4 classes to be used outside the package need to be listed in an exportClasses directive. Alternatively, they can be specified using exportClassPattern 66 in the same style as for exportPattern.

To export methods for generics from other packages an exportMethods directive can be used. Note that exporting methods on a generic in the namespace will also export the generic, and exporting a generic in the namespace will also export its methods. If the generic function is not local to this package, either because it was imported as a generic function or because the non-generic version has been made generic solely to add S4 methods to it as for functions such as coef in the example above , it can be declared via either or both of export or exportMethods , but the latter is clearer and is used in the stats4 example above.

In particular, for primitive functions there is no generic function, so export would export the primitive, which makes no sense. On the other hand, if the generic is local to this package, it is more natural to export the function itself using export , and this must be done if an implicit generic is created without setting any methods for it as is the case for AIC in stats4. A non-local generic function is only exported to ensure that calls to the function will dispatch the methods from this package and that is not done or required when the methods are for primitive functions.

For this reason, you do not need to document such implicitly created generic functions, and undoc in package tools will not report them. If a package uses S4 classes and methods exported from another package, but does not import the entire namespace of the other package 67 , it needs to import the classes and methods explicitly, with directives.

listing the classes and functions with methods respectively. Suppose we had two small packages A and B with B using A. Then they could have NAMESPACE files. Note that importMethodsFrom will also import any generics defined in the namespace on those methods. It is important if you export S4 methods that the corresponding generics are available. You may for example need to import coef from stats to make visible a function to be converted into its implicit generic. But it is better practice to make use of the generics exported by stats4 as this enables multiple packages to unambiguously set methods on those generics.

Next: Diagnostic messages , Previous: Package namespaces , Up: Creating R packages [ Contents ][ Index ]. This section contains advice on writing packages to be used on multiple platforms or for distribution for example to be submitted to a package repository such as CRAN.

Portable packages should have simple file names: use only alphanumeric ASCII characters and period. Many of the graphics devices are platform-specific: even X11 aka x11 which although emulated on Windows may not be available on a Unix-alike and is not the preferred screen device on OS X.

It is rarely necessary for package code or examples to open a new device, but if essential, 68 use dev. R CMD check provides a basic set of checks, but often further problems emerge when people try to install and use packages submitted to CRAN — many of these involve compiled code.

Here are some further checks that you can do to make your package more portable. Note that the -C flag for make is not included in the POSIX specification and is not implemented by some of the make s used with R.

which works in all versions of make known 71 to be used with R. and ensure that you use the value of environment variable MAKE and not just make in your scripts. On some platforms GNU make is available under a name such as gmake , and there SystemRequirements is used to set MAKE.

If you only need GNU make for parts of the package which are rarely needed for example to create bibliography files under vignettes , use a file called GNUmakefile rather than Makefile as GNU make only will use the former.

macOS has used GNU make for many years it previously used BSD make , but the version has been frozen at 3. Since the only viable make for Windows is GNU make, it is permissible to use GNU extensions in files Makevars.

win , Makevars. ucrt , Makefile. Using test -e or [ -e ] in shell scripts is not fully portable 74 : -f is normally what is intended. Flags -a and -o are nowadays declared obsolescent by POSIX and should not be used. The -o flag for set in shell scripts is optional in POSIX and not supported on all the platforms R is used on. Although R only requires Fortran 90, gfortran does not have a way to specify that standard. Not all common R platforms conform to the expected standards, e.

C99 for C code. It is very rare to need to output such types, and bit integers can usually be converted to doubles for output. However, the C11 standard section 7. h for example PRId64 so the portable approach is to test for these and if not available provide emulations in the package.

This can be used on other platforms with gcc or clang. If your package has a autoconf -generated configure script , try installing it whilst using this flag, and read through the config. log file — compilation warnings and errors can lead to features which are present not being detected. If possible do this on several platforms.

although -pthread is pretty close to portable. Option -U is portable but little use on the command line as it will only cancel built-in defines not portable and those defined earlier on the command line R does not use any.

This is unsafe for several reasons. Second, future versions of compilers may behave differently including updates to quite old series so for example -Werror and specializations can make a package non-installable under a future version. Third, using flags to suppress diagnostic messages can hide important information for debugging on a platform not tested by the package maintainer.

R CMD check can optionally report on unsafe flags which were used. For personal use -mtune is safer, but still not portable enough to be used in a public package.

It is not safe to assume that long and pointer types are the same size, and they are not on bit Windows. Note that integer in Fortran corresponds to int in C on all R platforms. and checking if any of the symbols marked U is unexpected is a good way to avoid this. A related issue is the naming of libraries built as part of the package installation. macOS and Windows have case-insensitive file systems, so using.

And -L. only appends to the list of searched locations, and liblz4 might be found in an earlier-searched location and has been. The only safe way is to give an explicit path, for example. Any confusion would be avoided by having LinkingTo headers in a directory named after the package. In any case, name conflicts of headers and directories under package include directories should be avoided, both between packages and between a package and system and third-party software.

ld -S invokes strip --strip-debug on GNU ld but is not portable: in particular on Solaris it does something completely different and takes an argument. When specifying a minimum Java version please use the official version names, which are confusingly. and as from a year. Fortunately only the integer values are likely to be relevant. A suitable test for Java at least version 8 for packages using rJava would be something like.

Note too that the compiler used to produce a jar can impose a minimum Java version, often resulting in an arcane message like.

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The Stangle function is replaced with a function that extracts the R source from a vignette. However, this code might not:. The functions in this section with the exception of math:pi are specified by reference to [IEEE ] , where they appear as Recommended operations in section 9. This definition excludes Unicode characters in the surrogate blocks as well as xFFFE and xFFFF, while including characters with codepoints greater than xFFFF which some programming languages treat as two characters. This prevents expenses of splitting very small programs into too many partitions. Do not reorder top-level functions, variables, and asm statements. This does not prevent the implementation distinguishing them internally, and triggering different · implementation-defined · warning conditions, but such distinctions do not affect the observable behavior of an application using the functions and operators defined in this specification.

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