firmware/common/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 /* find_first_set_bit() - this is a C version of the ffs algorithm devised
  25  * by D.Seal and posted to comp.sys.arm on  16 Feb 1994.
  26  *
  27  * Find the index of the least significant set bit in the word.
  28  * return values:
  29  *   0  - bit 0 is set
  30  *   1  - bit 1 is set
  31  *   ...
  32  *   31 - bit 31 is set
  33  *   32 - no bits set
  34  */
  35
  36 /* Table shared with assembly code */
  37 const uint8_t L_ffs_table[64] ICONST_ATTR =
  38 {
  39 /*   0   1   2   3   4   5   6   7           */
  40 /* ----------------------------------------- */
  41     32,  0,  1, 12,  2,  6,  0, 13, /*  0- 7 */
  42      3,  0,  7,  0,  0,  0,  0, 14, /*  8-15 */
  43     10,  4,  0,  0,  8,  0,  0, 25, /* 16-23 */
  44      0,  0,  0,  0,  0, 21, 27, 15, /* 24-31 */
  45     31, 11,  5,  0,  0,  0,  0,  0, /* 32-39 */
  46      9,  0,  0, 24,  0,  0, 20, 26, /* 40-47 */
  47     30,  0,  0,  0,  0, 23,  0, 19, /* 48-55 */
  48     29,  0, 22, 18, 28, 17, 16,  0, /* 56-63 */
  49 };
  50
  51 #if !defined(CPU_COLDFIRE)
  52 int find_first_set_bit(uint32_t val)
  53 {
  54     return L_ffs_table[((val & -val)*0x0450fbaf) >> 26];
  55 }
  56 #endif