135 lines
4.6 KiB
ArmAsm
135 lines
4.6 KiB
ArmAsm
/* ffs.s - find first set bit APIs for IA-32 architecture */
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/*
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* Copyright (c) 2011-2014 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 module implements the ffsMsb() and ffsLsb() functions for the IA-32
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architecture.
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INTERNAL
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Inline versions of these APIs, find_last_set_inline() and find_first_set_inline(),
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are defined in arch.h.
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*/
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#define _ASMLANGUAGE
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#include <arch/x86/asm.h>
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#include <offsets.h> /* nanokernel structure offset definitions */
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/* exports (public APIs) */
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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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* find_first_set - find first set bit searching from the LSB
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*
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* This routine finds the first bit set in the passed argument 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 to 32 for the most significant bit.
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* A return value of zero indicates that the value passed is zero.
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*
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* RETURNS: bit position from 1 to 32, or 0 if the argument is zero.
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*
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* INTERNAL
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* For Intel64 (x86_64) architectures, the 'cmovz' can be removed
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* and leverage the fact that the 'bsrl' doesn't modify the destination operand
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* when the source operand is zero. The "bitpos" variable can be preloaded
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* into the destination register, and given the unconditional ++bitpos that
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* is performed after the 'cmovz', the correct results are yielded.
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*/
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SECTION_FUNC(TEXT, find_first_set)
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#if !defined(CONFIG_CMOV_UNSUPPORTED)
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movl $0xffffffff, %ecx /* preload for 0 return value */
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bsfl 0x4(%esp), %eax /* bit scan "forward" */
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cmovz %ecx, %eax /* if operand == 0 then %ecx -> eax */
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addl $1, %eax
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ret
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#else
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bsfl 0x4(%esp), %eax /* bit scan "forward" */
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jnz ffsLsb_argNotZero
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xorl %eax, %eax /* return 0 when arg=0 */
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ret
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BRANCH_LABEL(ffsLsb_argNotZero) /* this label serves find_first_set() & find_last_set() */
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addl $1, %eax
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ret
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#endif /* !CONFIG_CMOV_UNSUPPORTED */
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/*******************************************************************************
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*
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* find_last_set - find first set bit searching from the MSB
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*
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* This routine finds the first bit set in the passed argument 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 to 32 for the most significant bit.
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* A return value of zero indicates that the value passed is zero.
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*
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* RETURNS: bit position from 1 to 32, or 0 if the argument is zero.
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*
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* INTERNAL
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* For Intel64 (x86_64) architectures, the 'cmovz' can be removed
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* and leverage the fact that the 'bsfl' doesn't modify the destination operand
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* when the source operand is zero. The "bitpos" variable can be preloaded
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* into the destination register, and given the unconditional ++bitpos that
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* is performed after the 'cmovz', the correct results are yielded.
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*/
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SECTION_FUNC(TEXT, find_last_set)
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#if !defined(CONFIG_CMOV_UNSUPPORTED)
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movl $0xffffffff, %ecx /* preload for 0 return value */
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bsrl 0x4(%esp), %eax /* bit scan "reverse" */
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cmovz %ecx, %eax /* if operand == 0 then %ecx -> eax */
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addl $1, %eax
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ret
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#else
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bsrl 0x4(%esp), %eax /* bit scan "reverse" */
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jnz ffsLsb_argNotZero
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xorl %eax, %eax /* return 0 when arg=0 */
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ret
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#endif /* !CONFIG_CMOV_UNSUPPORTED */
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