mingw-w64-crt/intrincs/bittest.c

#include <intrin.h>

unsigned char _bittest(long const *Base, long Offset)
{
  int old = 0;
  __asm__ __volatile__("btl %2,%1\n\tsbbl %0,%0 "
   :"=r" (old),"=m" ((*(volatile long *) Base))
   :"Ir" (Offset));
  return (old != 0);
}