GCC, ASM, BitScan

[serg_nifont]

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/***
  Serg Nifont
 
  GCC, Bit Scan forward and rewers with ASM inline
  (32 bit code)

  Idea get from ... sorry
***/


#include <stdio.h>
#include <stdlib.h>

typedef unsigned U32;


// i - in
// r - result
#define bsf(r, i) \
do { \
asm("bsf %1, %0" : "=r" (r) : "rm" (i)); \
} while(0)

U32 BSF32(U32 r){
  asm("bsf %1, %0" : "=r" (r) : "rm" (r)); \
  return r;
}

U32 BSR32(U32 r){
  asm("bsr %1, %0" : "=r" (r) : "rm" (r)); \
  return r;
}


#define GETFIRST(w) (U32)((w&0xFFFFFFFF) ? BSF32(w&0xFFFFFFFF) : (BSF32(w>>32)+32))
#define GETLAST(w)  (U32)((w>>32) ? BSR32(w>>32)+32 : BSR32(w&0xFFFFFFFF))
 
 
int main(int argc, char **argv) {
  U32  first,last,k;
  unsigned long long i;
 
  for(k = 0; k < 64; k++)
  {
    i = (1ULL<<k);// | (1ULL<<(63-k));
    //bsf(bit_n, i);
    first = GETFIRST(i);
    last  = GETLAST(i);
    printf("%u-%d-%d; ", k, first, last);
  }
  puts("");
return 0;
}