On December 26, 2014 6:05:34 PM CET, Bruce Momjian <br...@momjian.us> wrote: >On Fri, Dec 26, 2014 at 04:52:58PM +0100, Andres Freund wrote: >> On December 26, 2014 4:50:33 PM CET, Bruce Momjian <br...@momjian.us> >wrote: >> >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. >> >> That's the cpuid thing mentioned above. > >Oh, so cpuid is not a macro exported by the compiler but a C API. >Good
Neither, really. It's a instruction returning CPU capabilities. -- Please excuse brevity and formatting - I am writing this on my mobile phone. Andres Freund http://www.2ndQuadrant.com/ PostgreSQL Development, 24x7 Support, Training & Services -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
