59 lines
2.1 KiB
ArmAsm
59 lines
2.1 KiB
ArmAsm
/***************************************************************************
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* __________ __ ___.
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* Open \______ \ ____ ____ | | _\_ |__ _______ ___
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* Source | _// _ \_/ ___\| |/ /| __ \ / _ \ \/ /
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* Jukebox | | ( <_> ) \___| < | \_\ ( <_> > < <
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* Firmware |____|_ /\____/ \___ >__|_ \|___ /\____/__/\_ \
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* \/ \/ \/ \/ \/
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* $Id$
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*
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* Copyright (C) 2009 by Maurus Cuelenaere
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* based on ffs-arm.S by Michael Sevakis
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*
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* This program is free software; you can redistribute it and/or
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* modify it under the terms of the GNU General Public License
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* as published by the Free Software Foundation; either version 2
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* of the License, or (at your option) any later version.
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*
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* This software is distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY
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* KIND, either express or implied.
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*
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****************************************************************************/
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#include "config.h"
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#include "mips.h"
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/****************************************************************************
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* int find_first_set_bit(uint32_t val);
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*
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* Find the index of the least significant set bit in the 32-bit word.
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*
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* return values:
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* 0 - bit 0 is set
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* 1 - bit 1 is set
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* ...
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* 31 - bit 31 is set
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* 32 - no bits set
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****************************************************************************/
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.align 2
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.global find_first_set_bit
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.type find_first_set_bit, %function
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.set noreorder
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.set noat
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find_first_set_bit:
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beqz a0, l # if(a0 == 0) goto l
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nop #
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negu t0, a0 # t0 = -a0
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and t0, a0, t0 # t0 = a0 & t0
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clz v0, t0 # get lead 0's count
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li t0, 31 # t0 = 31
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jr ra #
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subu v0, t0, v0 # v0 = t0 - v0
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l:
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jr ra #
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li v0, 32 # v0 = 32
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.set reorder
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.set at
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