libc/string/ffs.c

   1 /*
   2  * Copyright (C) 2002     Manuel Novoa III
   3  * Copyright (C) 2000-2005 Erik Andersen <andersen@uclibc.org>
   4  *
   5  * Licensed under the LGPL v2.1, see the file COPYING.LIB in this tarball.
   6  */
   7
   8 #include <limits.h>
   9 #include <string.h>
  10
  11 int ffs(int i)
  12 {
  13 #if 1
  14         /* inlined binary search method */
  15         char n = 1;
  16 #if UINT_MAX == 0xffffU
  17         /* nothing to do here -- just trying to avoiding possible problems */
  18 #elif UINT_MAX == 0xffffffffU
  19         if (!(i & 0xffff)) {
  20                 n += 16;
  21                 i >>= 16;
  22         }
  23 #else
  24 #error ffs needs rewriting!
  25 #endif
  26
  27         if (!(i & 0xff)) {
  28                 n += 8;
  29                 i >>= 8;
  30         }
  31         if (!(i & 0x0f)) {
  32                 n += 4;
  33                 i >>= 4;
  34         }
  35         if (!(i & 0x03)) {
  36                 n += 2;
  37                 i >>= 2;
  38         }
  39         return (i) ? (n + ((i+1) & 0x01)) : 0;
  40
  41 #else
  42         /* linear search -- slow, but small */
  43         int n;
  44
  45         for (n = 0 ; i ; ++n) {
  46                 i >>= 1;
  47         }
  48
  49         return n;
  50 #endif
  51 }
  52 libc_hidden_def(ffs)
  53 #if ULONG_MAX == UINT_MAX
  54 strong_alias_untyped(ffs, ffsl)
  55 #endif