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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
21 lines
1.3 KiB
Markdown
21 lines
1.3 KiB
Markdown
Internal implementation of `memcpy` function.
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It has the following advantages over `libc`-supplied implementation:
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- it is linked statically, so the function is called directly, not through a `PLT` (procedure lookup table of shared library);
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- it is linked statically, so the function can have position-dependent code;
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- your binaries will not depend on `glibc`'s memcpy, that forces dependency on specific symbol version like `memcpy@@GLIBC_2.14` and consequently on specific version of `glibc` library;
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- you can include `memcpy.h` directly and the function has the chance to be inlined, which is beneficial for small but unknown at compile time sizes of memory regions;
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- this version of `memcpy` pretend to be faster (in our benchmarks, the difference is within few percents).
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Currently it uses the implementation from **Linwei** (skywind3000@163.com).
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Look at https://www.zhihu.com/question/35172305 for discussion.
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Drawbacks:
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- only use SSE 2, doesn't use wider (AVX, AVX 512) vector registers when available;
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- no CPU dispatching; doesn't take into account actual cache size.
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Also worth to look at:
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- simple implementation from Facebook: https://github.com/facebook/folly/blob/master/folly/memcpy.S
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- implementation from Agner Fog: http://www.agner.org/optimize/
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- glibc source code.
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