Volk: __cpuid_count() for MSVC

I noticed since last time (a year ago) I tried building
Volk using MSVC v16, the volk_cpu.tmp.c now uses the
gcc-centric function ‘__cpuid_count()’ which MSVC doesn’t
have.

I’m not really sure if the below patch is correct. But I
assume (from looking at gcc 5.1’s source) that the ECX should
be loaded with the ‘count’ value. So could it be patched into
something like this?

— a/volk/tmpl/volk_cpu.tmpl.c 2015-09-01 13:52:53
+++ b/volk_cpu.tmpl.c 2015-09-07 13:44:25
@@ -71,8 +71,16 @@

static inline unsigned int cpuid_count_x86_bit(unsigned int level,
unsigned int count, unsigned int reg, unsigned int
bit) {
#if defined(VOLK_CPU_x86)

  • #if defined(_MSC_VER) && defined(HAVE_INTRIN_H)
  •  int regs[4];
    
  •  __cpuidex(regs, level, count);
    
  • #elif defined(GNUC)
    unsigned int regs[4];
    __cpuid_count(level, count, regs[0], regs[1], regs[2], regs[3]);
  • #else
  •  #error No __cpuid()!
    
  • #endif
    return regs[reg] >> bit & 0x01;
    #else
    return 0;

Just to let you know.

The docs on MSVC’s __cpuidex() is here:
https://msdn.microsoft.com/en-us/library/vstudio/hskdteyh(v=vs.100).aspx


–gv

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