Editing Endianness (section)

=== Byte swapping ===

Byte-swapping consists of rearranging bytes to change endianness. Many compilers provide [[Intrinsic function|built-ins]] that are likely to be compiled into native processor instructions ({{code|bswap}}/{{code|movbe}}), such as {{code|__builtin_bswap32}}. Software interfaces for swapping include:

* Standard [[#Networking|network endianness]] functions (from/to BE, up to 32-bit).<ref>{{man|3|byteorder|Linux}}</ref> Windows has a 64-bit extension in {{code|winsock2.h}}.
* BSD and Glibc {{code|endian.h}} functions (from/to BE and LE, up to 64-bit).<ref>{{man|3|endian|Linux}}</ref>
* [[macOS]] {{code|OSByteOrder.h}} macros (from/to BE and LE, up to 64-bit).
* The {{code|std::byteswap}} function in [[C++23]].<ref>{{cite web |title=std::byteswap |url=https://en.cppreference.com/w/cpp/numeric/byteswap |website=en.cppreference.com |access-date=3 October 2023 |archive-date=20 November 2023 |archive-url=https://web.archive.org/web/20231120095109/https://en.cppreference.com/w/cpp/numeric/byteswap |url-status=live }}</ref>

Some [[CPU]] instruction sets provide native support for endian byte swapping, such as {{code|bswap}}<ref>{{cite web|url=http://www.intel.com/content/dam/www/public/us/en/documents/manuals/64-ia-32-architectures-software-developer-instruction-set-reference-manual-325383.pdf |archive-url=https://ghostarchive.org/archive/20221009/http://www.intel.com/content/dam/www/public/us/en/documents/manuals/64-ia-32-architectures-software-developer-instruction-set-reference-manual-325383.pdf |archive-date=2022-10-09 |url-status=live|title=Intel 64 and IA-32 Architectures Software Developer's Manual Volume 2 (2A, 2B & 2C): Instruction Set Reference, A-Z|at=p. 3–112|publisher=Intel|date=September 2016|access-date=2017-02-05}}</ref> ([[x86]] — [[Intel 80486|486]] and later, [[i960]] — i960Jx and later<ref>{{cite web|url=https://datasheets.chipdb.org/Intel/80960/manuals/27317301.PDF|title=i960® VH Processor Developer's Manual|publisher=Intel|date=October 1998|access-date=2024-04-02|archive-date=2024-04-02|archive-url=https://web.archive.org/web/20240402165236/https://datasheets.chipdb.org/Intel/80960/manuals/27317301.PDF|url-status=live}}</ref>), and {{code|rev}}<ref>{{cite web|url=http://infocenter.arm.com/help/topic/com.arm.doc.ddi0487a.k_10775/index.html|title=ARMv8-A Reference Manual|publisher=[[ARM Holdings]]|access-date=2017-02-05|archive-date=2019-01-19|archive-url=https://web.archive.org/web/20190119214452/http://infocenter.arm.com/help/topic/com.arm.doc.ddi0487a.k_10775/index.html|url-status=live}}</ref> ([[ARM architecture|ARMv6]] and later).

Some [[compiler]]s have built-in facilities for byte swapping. For example, the [[Intel]] [[Fortran]] compiler supports the non-standard {{code|CONVERT}} specifier when opening a file, e.g.: {{code|1=OPEN(unit, CONVERT='BIG_ENDIAN',...)|2=fortran|class=nowrap}}. Other compilers have options for generating code that globally enables the conversion for all file IO operations. This permits the reuse of code on a system with the opposite endianness without code modification.