Agner Fog:
> Choosing the most efficient function library can be a nightmare to a
> programmer. I have tried to calculate the cosine function with
> different libraries and compare the calculation time. The best
> version is 19 times faster than the worst!
>
> AMD have now updated their math libraries and added CPU dispatching.
> There are two versions of code in AMD's LIBM library: One for the
> SSE2 instruction set and one for AVX and FMA4. Intel processors will
> run the inferior SSE2 branch because they don't have the FMA4
> instruction set. The incompatibility between Intel's and AMD's FMA
> instructions is another scandal, which I have discussed in this blog
> post. The AMD library does not check the CPU brand name as Intel
> libraries do. It only checks for the FMA4 instructions which are not
> supported by Intel processors, although - quite ironically - they
> were designed by Intel. It will be possible to run the better branch
> on Intel processors if Intel decides to support the FMA4 instruction
> set in the future.
-- <http://agner.org/optimize/blog/read.php?i=209>
--
FUT: p.c.p