bitcnt_2.c

来自「国外网站上的一些精典的C程序」· C语言 代码 · 共 39 行

/*
**  Bit counter by Ratko Tomic
*/

#include "bitops.h"

int CDECL bitcount(long i)
{
      i = ((i & 0xAAAAAAAAL) >>  1) + (i & 0x55555555L);
      i = ((i & 0xCCCCCCCCL) >>  2) + (i & 0x33333333L);
      i = ((i & 0xF0F0F0F0L) >>  4) + (i & 0x0F0F0F0FL);
      i = ((i & 0xFF00FF00L) >>  8) + (i & 0x00FF00FFL);
      i = ((i & 0xFFFF0000L) >> 16) + (i & 0x0000FFFFL);
      return (int)i;
}

#ifdef TEST

#include <stdlib.h>
#include "snip_str.h"               /* For plural_text() macro    */

main(int argc, char *argv[])
{
      long n;

      while(--argc)
      {
            int i;

            n = atol(*++argv);
            i = bitcount(n);
            printf("%ld contains %d bit%s set\n",
                  n, i, plural_text(i));
      }
      return 0;
}

#endif /* TEST */