gonzui

    1: /*      $OpenBSD: ffs.c,v 1.7 2005/08/08 08:05:37 espie Exp $        */
    2: 
    3: /*
    4:  * Public domain.
    5:  * Written by Dale Rahn.
    6:  */
    7: 
    8: #if !defined(_KERNEL) && !defined(_STANDALONE)
    9: #include <string.h>
   10: #else
   11: #include <lib/libkern/libkern.h>
   12: #endif
   13: 
   14: /*
   15:  * ffs -- vax ffs instruction
   16:  */
   17: int
   18: ffs(int mask)
   19: {
   20:         int bit;
   21:         unsigned int r = mask;
   22:         static const signed char t[16] = {
   23:                 -28, 1, 2, 1,
   24:                   3, 1, 2, 1,
   25:                   4, 1, 2, 1,
   26:                   3, 1, 2, 1
   27:         };
   28: 
   29:         bit = 0;
   30:         if (!(r & 0xffff)) {
   31:                 bit += 16;
   32:                 r >>= 16;
   33:         }
   34:         if (!(r & 0xff)) {
   35:                 bit += 8;
   36:                 r >>= 8;
   37:         }
   38:         if (!(r & 0xf)) {
   39:                 bit += 4;
   40:                 r >>= 4;
   41:         }
   42: 
   43:         return (bit + t[ r & 0xf ]);
   44: }