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b7ef5a699c
* Get rid of non-existent vectorclass * Move FastMemcpy to contribs * Restore comments * Disable FastMemcpy on non-Linux * Fix cmake file * Don't build FastMemcpy for ARM64 * Replace FastMemcpy submodule with its contents * Fix cmake file * Move widechar_width to contrib/ * Move sumbur to contrib/ * Move consistent-hashing to contrib/ * Fix UBSan tests
1.3 KiB
1.3 KiB
Internal implementation of memcpy function.
It has the following advantages over libc-supplied implementation:
- it is linked statically, so the function is called directly, not through a
PLT(procedure lookup table of shared library); - it is linked statically, so the function can have position-dependent code;
- your binaries will not depend on
glibc's memcpy, that forces dependency on specific symbol version likememcpy@@GLIBC_2.14and consequently on specific version ofglibclibrary; - you can include
memcpy.hdirectly and the function has the chance to be inlined, which is beneficial for small but unknown at compile time sizes of memory regions; - this version of
memcpypretend to be faster (in our benchmarks, the difference is within few percents).
Currently it uses the implementation from Linwei (skywind3000@163.com). Look at https://www.zhihu.com/question/35172305 for discussion.
Drawbacks:
- only use SSE 2, doesn't use wider (AVX, AVX 512) vector registers when available;
- no CPU dispatching; doesn't take into account actual cache size.
Also worth to look at:
- simple implementation from Facebook: https://github.com/facebook/folly/blob/master/folly/memcpy.S
- implementation from Agner Fog: http://www.agner.org/optimize/
- glibc source code.