bitcnt_3.c

/*
**  BITCNT_3.C - Bit counting functions using table lookup
**
**  public domain by Auke Reitsma and Bruce Wedding
*/

#include "bitops.h"   /* from Snippets */

/*
**  Bits table
*/

static char bits[256] =
{
      0, 1, 1, 2, 1, 2, 2, 3, 1, 2, 2, 3, 2, 3, 3, 4,  /* 0   - 15  */
      1, 2, 2, 3, 2, 3, 3, 4, 2, 3, 3, 4, 3, 4, 4, 5,  /* 16  - 31  */
      1, 2, 2, 3, 2, 3, 3, 4, 2, 3, 3, 4, 3, 4, 4, 5,  /* 32  - 47  */
      2, 3, 3, 4, 3, 4, 4, 5, 3, 4, 4, 5, 4, 5, 5, 6,  /* 48  - 63  */
      1, 2, 2, 3, 2, 3, 3, 4, 2, 3, 3, 4, 3, 4, 4, 5,  /* 64  - 79  */
      2, 3, 3, 4, 3, 4, 4, 5, 3, 4, 4, 5, 4, 5, 5, 6,  /* 80  - 95  */
      2, 3, 3, 4, 3, 4, 4, 5, 3, 4, 4, 5, 4, 5, 5, 6,  /* 96  - 111 */
      3, 4, 4, 5, 4, 5, 5, 6, 4, 5, 5, 6, 5, 6, 6, 7,  /* 112 - 127 */
      1, 2, 2, 3, 2, 3, 3, 4, 2, 3, 3, 4, 3, 4, 4, 5,  /* 128 - 143 */
      2, 3, 3, 4, 3, 4, 4, 5, 3, 4, 4, 5, 4, 5, 5, 6,  /* 144 - 159 */
      2, 3, 3, 4, 3, 4, 4, 5, 3, 4, 4, 5, 4, 5, 5, 6,  /* 160 - 175 */
      3, 4, 4, 5, 4, 5, 5, 6, 4, 5, 5, 6, 5, 6, 6, 7,  /* 176 - 191 */
      2, 3, 3, 4, 3, 4, 4, 5, 3, 4, 4, 5, 4, 5, 5, 6,  /* 192 - 207 */
      3, 4, 4, 5, 4, 5, 5, 6, 4, 5, 5, 6, 5, 6, 6, 7,  /* 208 - 223 */
      3, 4, 4, 5, 4, 5, 5, 6, 4, 5, 5, 6, 5, 6, 6, 7,  /* 224 - 239 */
      4, 5, 5, 6, 5, 6, 6, 7, 5, 6, 6, 7, 6, 7, 7, 8   /* 240 - 255 */
};

/*
**  Count bits in each nybble
**
**  Note: Only the first 16 table entries are used, the rest could be
**        omitted.
*/

int CDECL ntbl_bitcount(long int x)
{
      return
            bits[ (int) (x & 0x0000000FUL)       ] +
            bits[ (int)((x & 0x000000F0UL) >> 4) ] +
            bits[ (int)((x & 0x00000F00UL) >> 8) ] +
            bits[ (int)((x & 0x0000F000UL) >> 12)] +
            bits[ (int)((x & 0x000F0000UL) >> 16)] +
            bits[ (int)((x & 0x00F00000UL) >> 20)] +
            bits[ (int)((x & 0x0F000000UL) >> 24)] +
            bits[ (int)((x & 0xF0000000UL) >> 28)];
}

/*
**  Count bits in each byte
**
**  by Bruce Wedding, works best on Watcom & Borland
*/

int CDECL BW_btbl_bitcount(long int x)
{
      union 
      { 
            unsigned char ch[4]; 
            long y; 
      } U; 
 
      U.y = x; 
 
      return bits[ U.ch[0] ] + bits[ U.ch[1] ] + 
             bits[ U.ch[3] ] + bits[ U.ch[2] ]; 
}

/*
**  Count bits in each byte
**
**  by Auke Reitsma, works best on Microsoft, Symantec, and others
*/

int CDECL AR_btbl_bitcount(long int x)
{
      unsigned char * Ptr = (unsigned char *) &x ;
      int Accu ;

      Accu  = bits[ *Ptr++ ];
      Accu += bits[ *Ptr++ ];
      Accu += bits[ *Ptr++ ];
      Accu += bits[ *Ptr ];
      return Accu;
}

#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 = BW_btbl_bitcount(n);
            printf("%ld contains %d bit%s set\n",
                  n, i, plural_text(i));
            i = AR_btbl_bitcount(n);
            printf("%ld contains %d bit%s set\n",
                  n, i, plural_text(i));
      }
      return 0;
}

#endif /* TEST */