firmware/asm/ffs.c

   1 /***************************************************************************
   2  *             __________               __   ___.
   3  *   Open      \______   \ ____   ____ |  | _\_ |__   _______  ___
   4  *   Source     |       _//  _ \_/ ___\|  |/ /| __ \ /  _ \  \/  /
   5  *   Jukebox    |    |   (  <_> )  \___|    < | \_\ (  <_> > <  <
   6  *   Firmware   |____|_  /\____/ \___  >__|_ \|___  /\____/__/\_ \
   7  *                     \/            \/     \/    \/            \/
   8  * $Id$
   9  *
  10  * Copyright (C) 2008 by Michael Sevakis
  11  *
  12  * This program is free software; you can redistribute it and/or
  13  * modify it under the terms of the GNU General Public License
  14  * as published by the Free Software Foundation; either version 2
  15  * of the License, or (at your option) any later version.
  16  *
  17  * This software is distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY
  18  * KIND, either express or implied.
  19  *
  20  ****************************************************************************/
  21 #include "config.h"
  22 #include <inttypes.h>
  23
  24 /*
  25  * Find the index of the least significant set bit in the word.
  26  * return values:
  27  *   0  - bit 0 is set
  28  *   1  - bit 1 is set
  29  *   ...
  30  *   31 - bit 31 is set
  31  *   32 - no bits set
  32  */
  33 int find_first_set_bit(uint32_t val)
  34 {
  35     if (val == 0)
  36         return 32;
  37
  38     /* __builtin_ctz[l[l]]: Returns the number of trailing 0-bits in x,
  39      * starting at the least significant bit position. If x is 0, the result
  40      * is undefined. */
  41     return __builtin_ctz(val);
  42 }