259 строки
7.0 KiB
ArmAsm
259 строки
7.0 KiB
ArmAsm
/*
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* Copyright (C) 2013 ARM Ltd.
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* Copyright (C) 2013 Linaro.
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*
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* This code is based on glibc cortex strings work originally authored by Linaro
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* and re-licensed under GPLv2 for the Linux kernel. The original code can
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* be found @
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*
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* http://bazaar.launchpad.net/~linaro-toolchain-dev/cortex-strings/trunk/
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* files/head:/src/aarch64/
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*
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License version 2 as
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* published by the Free Software Foundation.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program. If not, see <http://www.gnu.org/licenses/>.
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*/
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#include <linux/linkage.h>
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#include <asm/assembler.h>
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/*
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* compare memory areas(when two memory areas' offset are different,
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* alignment handled by the hardware)
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*
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* Parameters:
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* x0 - const memory area 1 pointer
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* x1 - const memory area 2 pointer
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* x2 - the maximal compare byte length
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* Returns:
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* x0 - a compare result, maybe less than, equal to, or greater than ZERO
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*/
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/* Parameters and result. */
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src1 .req x0
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src2 .req x1
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limit .req x2
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result .req x0
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/* Internal variables. */
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data1 .req x3
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data1w .req w3
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data2 .req x4
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data2w .req w4
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has_nul .req x5
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diff .req x6
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endloop .req x7
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tmp1 .req x8
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tmp2 .req x9
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tmp3 .req x10
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pos .req x11
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limit_wd .req x12
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mask .req x13
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ENTRY(memcmp)
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cbz limit, .Lret0
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eor tmp1, src1, src2
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tst tmp1, #7
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b.ne .Lmisaligned8
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ands tmp1, src1, #7
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b.ne .Lmutual_align
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sub limit_wd, limit, #1 /* limit != 0, so no underflow. */
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lsr limit_wd, limit_wd, #3 /* Convert to Dwords. */
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/*
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* The input source addresses are at alignment boundary.
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* Directly compare eight bytes each time.
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*/
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.Lloop_aligned:
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ldr data1, [src1], #8
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ldr data2, [src2], #8
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.Lstart_realigned:
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subs limit_wd, limit_wd, #1
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eor diff, data1, data2 /* Non-zero if differences found. */
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csinv endloop, diff, xzr, cs /* Last Dword or differences. */
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cbz endloop, .Lloop_aligned
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/* Not reached the limit, must have found a diff. */
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tbz limit_wd, #63, .Lnot_limit
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/* Limit % 8 == 0 => the diff is in the last 8 bytes. */
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ands limit, limit, #7
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b.eq .Lnot_limit
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/*
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* The remained bytes less than 8. It is needed to extract valid data
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* from last eight bytes of the intended memory range.
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*/
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lsl limit, limit, #3 /* bytes-> bits. */
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mov mask, #~0
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CPU_BE( lsr mask, mask, limit )
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CPU_LE( lsl mask, mask, limit )
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bic data1, data1, mask
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bic data2, data2, mask
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orr diff, diff, mask
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b .Lnot_limit
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.Lmutual_align:
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/*
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* Sources are mutually aligned, but are not currently at an
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* alignment boundary. Round down the addresses and then mask off
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* the bytes that precede the start point.
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*/
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bic src1, src1, #7
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bic src2, src2, #7
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ldr data1, [src1], #8
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ldr data2, [src2], #8
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/*
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* We can not add limit with alignment offset(tmp1) here. Since the
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* addition probably make the limit overflown.
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*/
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sub limit_wd, limit, #1/*limit != 0, so no underflow.*/
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and tmp3, limit_wd, #7
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lsr limit_wd, limit_wd, #3
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add tmp3, tmp3, tmp1
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add limit_wd, limit_wd, tmp3, lsr #3
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add limit, limit, tmp1/* Adjust the limit for the extra. */
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lsl tmp1, tmp1, #3/* Bytes beyond alignment -> bits.*/
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neg tmp1, tmp1/* Bits to alignment -64. */
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mov tmp2, #~0
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/*mask off the non-intended bytes before the start address.*/
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CPU_BE( lsl tmp2, tmp2, tmp1 )/*Big-endian.Early bytes are at MSB*/
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/* Little-endian. Early bytes are at LSB. */
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CPU_LE( lsr tmp2, tmp2, tmp1 )
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orr data1, data1, tmp2
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orr data2, data2, tmp2
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b .Lstart_realigned
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/*src1 and src2 have different alignment offset.*/
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.Lmisaligned8:
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cmp limit, #8
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b.lo .Ltiny8proc /*limit < 8: compare byte by byte*/
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and tmp1, src1, #7
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neg tmp1, tmp1
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add tmp1, tmp1, #8/*valid length in the first 8 bytes of src1*/
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and tmp2, src2, #7
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neg tmp2, tmp2
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add tmp2, tmp2, #8/*valid length in the first 8 bytes of src2*/
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subs tmp3, tmp1, tmp2
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csel pos, tmp1, tmp2, hi /*Choose the maximum.*/
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sub limit, limit, pos
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/*compare the proceeding bytes in the first 8 byte segment.*/
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.Ltinycmp:
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ldrb data1w, [src1], #1
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ldrb data2w, [src2], #1
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subs pos, pos, #1
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ccmp data1w, data2w, #0, ne /* NZCV = 0b0000. */
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b.eq .Ltinycmp
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cbnz pos, 1f /*diff occurred before the last byte.*/
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cmp data1w, data2w
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b.eq .Lstart_align
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1:
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sub result, data1, data2
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ret
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.Lstart_align:
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lsr limit_wd, limit, #3
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cbz limit_wd, .Lremain8
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ands xzr, src1, #7
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b.eq .Lrecal_offset
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/*process more leading bytes to make src1 aligned...*/
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add src1, src1, tmp3 /*backwards src1 to alignment boundary*/
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add src2, src2, tmp3
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sub limit, limit, tmp3
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lsr limit_wd, limit, #3
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cbz limit_wd, .Lremain8
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/*load 8 bytes from aligned SRC1..*/
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ldr data1, [src1], #8
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ldr data2, [src2], #8
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subs limit_wd, limit_wd, #1
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eor diff, data1, data2 /*Non-zero if differences found.*/
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csinv endloop, diff, xzr, ne
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cbnz endloop, .Lunequal_proc
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/*How far is the current SRC2 from the alignment boundary...*/
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and tmp3, tmp3, #7
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.Lrecal_offset:/*src1 is aligned now..*/
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neg pos, tmp3
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.Lloopcmp_proc:
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/*
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* Divide the eight bytes into two parts. First,backwards the src2
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* to an alignment boundary,load eight bytes and compare from
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* the SRC2 alignment boundary. If all 8 bytes are equal,then start
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* the second part's comparison. Otherwise finish the comparison.
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* This special handle can garantee all the accesses are in the
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* thread/task space in avoid to overrange access.
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*/
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ldr data1, [src1,pos]
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ldr data2, [src2,pos]
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eor diff, data1, data2 /* Non-zero if differences found. */
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cbnz diff, .Lnot_limit
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/*The second part process*/
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ldr data1, [src1], #8
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ldr data2, [src2], #8
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eor diff, data1, data2 /* Non-zero if differences found. */
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subs limit_wd, limit_wd, #1
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csinv endloop, diff, xzr, ne/*if limit_wd is 0,will finish the cmp*/
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cbz endloop, .Lloopcmp_proc
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.Lunequal_proc:
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cbz diff, .Lremain8
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/* There is difference occurred in the latest comparison. */
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.Lnot_limit:
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/*
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* For little endian,reverse the low significant equal bits into MSB,then
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* following CLZ can find how many equal bits exist.
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*/
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CPU_LE( rev diff, diff )
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CPU_LE( rev data1, data1 )
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CPU_LE( rev data2, data2 )
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/*
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* The MS-non-zero bit of DIFF marks either the first bit
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* that is different, or the end of the significant data.
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* Shifting left now will bring the critical information into the
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* top bits.
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*/
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clz pos, diff
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lsl data1, data1, pos
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lsl data2, data2, pos
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/*
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* We need to zero-extend (char is unsigned) the value and then
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* perform a signed subtraction.
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*/
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lsr data1, data1, #56
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sub result, data1, data2, lsr #56
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ret
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.Lremain8:
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/* Limit % 8 == 0 =>. all data are equal.*/
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ands limit, limit, #7
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b.eq .Lret0
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.Ltiny8proc:
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ldrb data1w, [src1], #1
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ldrb data2w, [src2], #1
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subs limit, limit, #1
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ccmp data1w, data2w, #0, ne /* NZCV = 0b0000. */
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b.eq .Ltiny8proc
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sub result, data1, data2
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ret
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.Lret0:
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mov result, #0
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ret
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ENDPIPROC(memcmp)
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