94 lines
2.9 KiB
ArmAsm
94 lines
2.9 KiB
ArmAsm
/* ffs.S - ARM find first set assembly routines */
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/*
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* Copyright (c) 2013-2014 Wind River Systems, Inc.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions are met:
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*
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* 1) Redistributions of source code must retain the above copyright notice,
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* this list of conditions and the following disclaimer.
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*
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* 2) Redistributions in binary form must reproduce the above copyright notice,
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* this list of conditions and the following disclaimer in the documentation
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* and/or other materials provided with the distribution.
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*
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* 3) Neither the name of Wind River Systems nor the names of its contributors
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* may be used to endorse or promote products derived from this software without
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* specific prior written permission.
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*
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* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
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* AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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* ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE
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* LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
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* CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
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* SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
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* INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
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* CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
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* ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
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* POSSIBILITY OF SUCH DAMAGE.
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*/
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/*
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DESCRIPTION
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This library implements find_last_set() and find_first_set() which returns the
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most and least significant bit set respectively.
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*/
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#define _ASMLANGUAGE
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#include <toolchain.h>
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#include <sections.h>
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_ASM_FILE_PROLOGUE
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/* Exports */
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GTEXT(find_last_set)
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GTEXT(find_first_set)
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/**
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*
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* @brief Find first set bit (searching from the most significant bit)
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*
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* This routine finds the first bit set in the argument passed it and
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* returns the index of that bit. Bits are numbered starting
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* at 1 from the least significant bit. A return value of zero indicates that
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* the value passed is zero.
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*
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* @return most significant bit set
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*/
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SECTION_FUNC(TEXT, find_last_set)
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cmp r0, #0
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itt ne
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clzne r0, r0
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rsbne r0, r0, #32
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mov pc, lr
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/**
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*
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* @brief Find first set bit (searching from the least significant bit)
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*
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* This routine finds the first bit set in the argument passed it and
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* returns the index of that bit. Bits are numbered starting
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* at 1 from the least significant bit. A return value of zero indicates that
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* the value passed is zero.
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*
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* @return least significant bit set
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*/
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SECTION_FUNC(TEXT, find_first_set)
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rsb r1, r0, #0
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ands r0, r1, r0 /* r0 = x & (-x): only LSB set */
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itt ne
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clzne r0, r0 /* count leading zeroes */
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rsbne r0, r0, #32
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mov pc, lr
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