missing/ffs.c

   1 /* ffs.c - find first set bit */
   2 /* ffs() is defined by Single Unix Specification. */
   3
   4 #include "ruby.h"
   5
   6 int ffs(int arg)
   7 {
   8     unsigned int x = (unsigned int)arg;
   9     int r;
  10
  11     if (x == 0)
  12         return 0;
  13
  14     r = 1;
  15
  16 #if 32 < SIZEOF_INT * CHAR_BIT
  17     if ((x & 0xffffffff) == 0) {
  18         x >>= 32;
  19         r += 32;
  20     }
  21 #endif
  22
  23     if ((x & 0xffff) == 0) {
  24         x >>= 16;
  25         r += 16;
  26     }
  27
  28     if ((x & 0xff) == 0) {
  29         x >>= 8;
  30         r += 8;
  31     }
  32
  33     if ((x & 0xf) == 0) {
  34         x >>= 4;
  35         r += 4;
  36     }
  37
  38     if ((x & 0x3) == 0) {
  39         x >>= 2;
  40         r += 2;
  41     }
  42
  43     if ((x & 0x1) == 0) {
  44         x >>= 1;
  45         r += 1;
  46     }
  47
  48     return r;
  49 }