| /*************************************************************************** |
| * __________ __ ___. |
| * Open \______ \ ____ ____ | | _\_ |__ _______ ___ |
| * Source | _// _ \_/ ___\| |/ /| __ \ / _ \ \/ / |
| * Jukebox | | ( <_> ) \___| < | \_\ ( <_> > < < |
| * Firmware |____|_ /\____/ \___ >__|_ \|___ /\____/__/\_ \ |
| * \/ \/ \/ \/ \/ |
| * $Id$ |
| * |
| * Copyright (C) 2008 by Michael Sevakis |
| * |
| * This program is free software; you can redistribute it and/or |
| * modify it under the terms of the GNU General Public License |
| * as published by the Free Software Foundation; either version 2 |
| * of the License, or (at your option) any later version. |
| * |
| * This software is distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY |
| * KIND, either express or implied. |
| * |
| ****************************************************************************/ |
| #include "config.h" |
| |
| /**************************************************************************** |
| * int find_first_set_bit(uint32_t val); |
| * |
| * Find the index of the least significant set bit in the 32-bit word. |
| * |
| * return values: |
| * 0 - bit 0 is set |
| * 1 - bit 1 is set |
| * ... |
| * 31 - bit 31 is set |
| * 32 - no bits set |
| ****************************************************************************/ |
| .text |
| .align 2 |
| .global find_first_set_bit |
| .type find_first_set_bit,@function |
| find_first_set_bit: |
| | this is a coldfire version of the ffs algorithm devised by D.Seal |
| | and posted to comp.sys.arm on 16 Feb 1994. |
| | |
| | Output modified to suit rockbox purposes. |
| |
| | Standard trick to isolate bottom bit in r0 or 0 if r0 = 0 on entry |
| move.l 4(%sp), %d1 | %d1 = %d1 & -%d1 |
| lea.l L_ffs_table, %a0 | %a0 = table address |
| move.l %d1, %d0 | |
| neg.l %d1 | |
| and.l %d0, %d1 | |
| |
| | now %d1 has at most one set bit, call this X |
| |
| move.l #0x0450fbaf, %d0 | %d0 = multiplier |
| mulu.l %d0, %d1 | %d1 = X * 0x0450fbaf |
| |
| | now lookup in table indexed on top 6 bits of %d0 |
| moveq.l #26, %d0 | %d0 = final shift count |
| lsr.l %d0, %d1 | |
| clr.l %d0 | |
| move.b (%a0, %d1.l), %d0 | |
| rts | |
| |
| .size find_first_set_bit, .-find_first_set_bit |