Bruno Haible via Gnulib discussion list <bug-gnulib@gnu.org> writes: > Simon Josefsson wrote: >> I think in this example, I think it makes >> sense for gnulib to provide a optimized CRC function that may contain >> architecture-specific optimizations. The reason seems to be that while >> there are numerous different optimized implementations around, few seems >> to be arranged in a re-usable fashion. >> >> The barrier for acceptance in gnulib may be higher than in some >> individual projects since gnulib is intended to be highly portable and >> flexible, and this requires extra care when doing the implementation. >> But there are examples of arch-specific assembler code in gnulib >> already. > > I agree. In this case, it makes sense to have special optimizations for > particular CPUs because it's such a bottleneck for gzip and because > these optimizations are significant: > - pclmul (x86_64) twice as fast [1], > - crc32[bhwx] (arm64) [2] five times as fast [3] > or pmull [4]. > > For maintainability, it does not seem wise to have sizeable portions > of assembly-language code for different CPUs in the same source file. > I would therefore suggest these file names: > lib/crc.c for the generic C code, > lib/crc-x64_64.h for the x86_64 code, > libcrc-arm64.h for the arm64 code.
+1 > But first, we need to have the slice-by-8 as portable code in lib/crc.c. If we are splitting this module up into several, maybe it even make more sense to have a 'crc-slice-by-8' module for that particular portable optimization. I have one use-case (although not published so less important) where the table size increase is a problem, and would prefer to use the current smaller crc.c (or even better, a smaller one that generate the tables on the fly, I forgot that it is possible). But, yes, let's take things step by step. /Simon > Bruno > > [1] https://lists.gnu.org/archive/html/bug-gnulib/2024-10/msg00095.html > [2] > https://developer.arm.com/documentation/dui0801/h/A64-General-Instructions/CRC32B--CRC32H--CRC32W--CRC32X > [3] > https://patchwork.kernel.org/project/linux-crypto/patch/1416417577-27495-1-git-send-email-yazen.ghan...@linaro.org/ > [4] https://lwn.net/Articles/994292/ > > > > >
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