[walki]

> it’s good for software robustness that file formats and hardware use different endianness, as it forces you to read things byte-by-byte rather than lazily assuming you can just read 4 bytes and cast them directly to an int32.

Except that it is very bad for performance. As far as CPUs are concerned little-endian has definitely won, most CPU architectures that have been big endian in the past (e.g. PowerPC) are now little endian by default.

If all new CPU architectures are little endian this means that within a decade or two there won't be any operating systems that support big endian anymore.

[classichasclass]

Power ISA is actually still big by default, and even on little-endian capable systems starts big endian until changed by the OS. Low-level OPAL calls on OpenPOWER systems are made big endian, even if the OS is little (the OS has to switch the processor mode).

[iainmerrick]

For performance, can’t you “just” have a swap-endianness instruction in your CPU, and have the compiler use it when it detects byte-shuffling code?

(That may even happen already on some architectures for all I know)

[walki]

> For performance, can’t you “just” have a swap-endianness instruction in your CPU

Yes, most CPUs have special instructions for swapping between little and big endian byte arrangement. The GCC compiler has the __builtin_bswap64(x) for accessing this instruction. However this is an additional instruction that needs to be executed for each read of a 64-bit word that needs to be converted, in some workloads this can double the number of executed instructions and hence add significant overhead.

Supporting big endian CPUs in systems programming sucks beyond imagination. There are virtually no big endian users anymore and making sure your software works fine on big endian requires testing it on a big endian CPU. However it is not possible to buy a big endian CPU anymore as there exist no more consumer big endian CPUs. For this reason I still have a Mac PowerPC from 2003 at home running an ancient version of Mac OS X. But over the last 2 years I have stopped testing my software on big endian, I just don't care about big endian anymore...