avx detection

avx.c

#include <stdio.h>

// https://en.wikipedia.org/wiki/CPUID
static void cpuid(int cpu_info[4], int info_type) {
  __asm__ volatile("cpuid \n\t"
                   : "=a"(cpu_info[0]),
                     "=b"(cpu_info[1]),
                     "=c"(cpu_info[3]),
                     "=d"(cpu_info[2])
                   : "a"(info_type), "c"(0));
}

int main() {
  int cpu_info[5] = {0};
  int cpu_info7[4] = {0};
  cpuid(cpu_info, 0);
  int len = cpu_info[0];
  printf("vendor=%s\n", (char*) &cpu_info[1]);
  if (len > 0) {
    cpuid(cpu_info, 1);
    if (len >= 7) {
      cpuid(cpu_info7, 7);
    }
  }
  int has_avx = (cpu_info[3] & (1 << 28)) != 0;
  int has_avx2 = (cpu_info7[1] & (1 << 5)) != 0;
  printf("avx=%d\n", has_avx);
  printf("avx2=%d\n", has_avx2);
}