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by dataflow 1533 days ago
See [1], or [2] and [3].

[1] https://github.com/as-com/varint-simd/blob/f4c4af672403cc683...

[2] https://en.wikipedia.org/wiki/X86_Bit_manipulation_instructi...

[3] https://en.wikipedia.org/wiki/List_of_AMD_CPU_microarchitect...
1 comments
tedunangst 1533 days ago
So... ignore the cpuid bit indicating the instruction is present and look at manufacturer string, which is exactly what intel is being lambasted for here.
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dataflow 1533 days ago
No, you don't ignore the CPUID feature bit. You use the CPUID to enable the feature by default, but override that default by blacklisting specific models that you know would have undesirable implementations.

So what you would do for PDEP/PEXT would be

  use_pdep = cpuid.supports_bmi2() && !cpuid.is_amd_before_zen3()
and not

  use_pdep = cpuid.is_intel_haswell_or_later()
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