Re: What exactly is our CRC algorithm?

On Thu, Dec 25, 2014 at 11:57:29AM +0530, Abhijit Menon-Sen wrote:
> Hi.
>
> Here's a proposed patch to use CPUID at startup to determine if the
> SSE4.2 CRC instructions are available, to use them instead of the
> slice-by-8 implementation (posted earlier).
>
> A few notes:
>
> 1. GCC has included cpuid.h since 4.3.0, so I figured it was safe to
> use. It can be replaced with some inline assembly otherwise.
>
> 2. I've also used the crc32b/crc32q instructions directly rather than
> using ".bytes" to encode the instructions; bintuils versions since
> 2007 or so have supported them.
>
> 3. I've included the MSVC implementation mostly as an example of how to
> extend this to different compilers/platforms. It's written according
> to the documentation for MSVC intrinsics, but I have not tested it.
> Suggestions/improvements are welcome.

Uh, what happens if the system is compiled on a different CPU that it is
run on? Seems we would need a run-time CPU test.

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Bruce Momjian <bruce(at)momjian(dot)us> http://momjian.us
EnterpriseDB http://enterprisedb.com

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