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This is an optimized memcmp for AArch64. This is a complete rewrite using a different algorithm. The previous version split into cases where both inputs were aligned, the inputs were mutually aligned and unaligned using a byte loop. The new version combines all these cases, while small inputs of less than 8 bytes are handled separately. This allows the main code to be sped up using unaligned loads since there are now at least 8 bytes to be compared. After the first 8 bytes, align the first input. This ensures each iteration does at most one unaligned access and mutually aligned inputs behave as aligned. After the main loop, process the last 8 bytes using unaligned accesses. This improves performance of (mutually) aligned cases by 25% and unaligned by >500% (yes >6 times faster) on large inputs.
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| /* SPDX-License-Identifier: GPL-2.0-only */ | ||
| /* | ||
| * Copyright (C) 2013 ARM Ltd. | ||
| * Copyright (C) 2013 Linaro. | ||
| * Copyright (c) 2017 ARM Ltd | ||
| * All rights reserved. | ||
| * | ||
| * This code is based on glibc cortex strings work originally authored by Linaro | ||
| * be found @ | ||
| * Redistribution and use in source and binary forms, with or without | ||
| * modification, are permitted provided that the following conditions | ||
| * are met: | ||
| * 1. Redistributions of source code must retain the above copyright | ||
| * notice, this list of conditions and the following disclaimer. | ||
| * 2. Redistributions in binary form must reproduce the above copyright | ||
| * notice, this list of conditions and the following disclaimer in the | ||
| * documentation and/or other materials provided with the distribution. | ||
| * 3. The name of the company may not be used to endorse or promote | ||
| * products derived from this software without specific prior written | ||
| * permission. | ||
| * | ||
| * http://bazaar.launchpad.net/~linaro-toolchain-dev/cortex-strings/trunk/ | ||
| * files/head:/src/aarch64/ | ||
| * THIS SOFTWARE IS PROVIDED BY ARM LTD ``AS IS'' AND ANY EXPRESS OR IMPLIED | ||
| * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF | ||
| * MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. | ||
| * IN NO EVENT SHALL ARM LTD BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, | ||
| * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED | ||
| * TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR | ||
| * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF | ||
| * LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING | ||
| * NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS | ||
| * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. | ||
| */ | ||
|
|
||
| /* Assumptions: | ||
| * | ||
| * ARMv8-a, AArch64, unaligned accesses. | ||
| */ | ||
|
|
||
| /* includes here */ | ||
| #include <linux/linkage.h> | ||
| #include <asm/assembler.h> | ||
|
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||
| /* | ||
| * compare memory areas(when two memory areas' offset are different, | ||
| * alignment handled by the hardware) | ||
| * | ||
| * Parameters: | ||
| * x0 - const memory area 1 pointer | ||
| * x1 - const memory area 2 pointer | ||
| * x2 - the maximal compare byte length | ||
| * Returns: | ||
| * x0 - a compare result, maybe less than, equal to, or greater than ZERO | ||
| */ | ||
|
|
||
| /* Parameters and result. */ | ||
| src1 .req x0 | ||
| src2 .req x1 | ||
| limit .req x2 | ||
| result .req x0 | ||
| #define src1 x0 | ||
| #define src2 x1 | ||
| #define limit x2 | ||
| #define result w0 | ||
|
|
||
| /* Internal variables. */ | ||
| data1 .req x3 | ||
| data1w .req w3 | ||
| data2 .req x4 | ||
| data2w .req w4 | ||
| has_nul .req x5 | ||
| diff .req x6 | ||
| endloop .req x7 | ||
| tmp1 .req x8 | ||
| tmp2 .req x9 | ||
| tmp3 .req x10 | ||
| pos .req x11 | ||
| limit_wd .req x12 | ||
| mask .req x13 | ||
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| SYM_FUNC_START_WEAK_PI(memcmp) | ||
| cbz limit, .Lret0 | ||
| eor tmp1, src1, src2 | ||
| tst tmp1, #7 | ||
| b.ne .Lmisaligned8 | ||
| ands tmp1, src1, #7 | ||
| b.ne .Lmutual_align | ||
| sub limit_wd, limit, #1 /* limit != 0, so no underflow. */ | ||
| lsr limit_wd, limit_wd, #3 /* Convert to Dwords. */ | ||
| /* | ||
| * The input source addresses are at alignment boundary. | ||
| * Directly compare eight bytes each time. | ||
| */ | ||
| .Lloop_aligned: | ||
| ldr data1, [src1], #8 | ||
| ldr data2, [src2], #8 | ||
| .Lstart_realigned: | ||
| subs limit_wd, limit_wd, #1 | ||
| eor diff, data1, data2 /* Non-zero if differences found. */ | ||
| csinv endloop, diff, xzr, cs /* Last Dword or differences. */ | ||
| cbz endloop, .Lloop_aligned | ||
|
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||
| /* Not reached the limit, must have found a diff. */ | ||
| tbz limit_wd, #63, .Lnot_limit | ||
|
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| /* Limit % 8 == 0 => the diff is in the last 8 bytes. */ | ||
| ands limit, limit, #7 | ||
| b.eq .Lnot_limit | ||
| /* | ||
| * The remained bytes less than 8. It is needed to extract valid data | ||
| * from last eight bytes of the intended memory range. | ||
| */ | ||
| lsl limit, limit, #3 /* bytes-> bits. */ | ||
| mov mask, #~0 | ||
| CPU_BE( lsr mask, mask, limit ) | ||
| CPU_LE( lsl mask, mask, limit ) | ||
| bic data1, data1, mask | ||
| bic data2, data2, mask | ||
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| orr diff, diff, mask | ||
| b .Lnot_limit | ||
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| .Lmutual_align: | ||
| /* | ||
| * Sources are mutually aligned, but are not currently at an | ||
| * alignment boundary. Round down the addresses and then mask off | ||
| * the bytes that precede the start point. | ||
| */ | ||
| bic src1, src1, #7 | ||
| bic src2, src2, #7 | ||
| ldr data1, [src1], #8 | ||
| ldr data2, [src2], #8 | ||
| /* | ||
| * We can not add limit with alignment offset(tmp1) here. Since the | ||
| * addition probably make the limit overflown. | ||
| */ | ||
| sub limit_wd, limit, #1/*limit != 0, so no underflow.*/ | ||
| and tmp3, limit_wd, #7 | ||
| lsr limit_wd, limit_wd, #3 | ||
| add tmp3, tmp3, tmp1 | ||
| add limit_wd, limit_wd, tmp3, lsr #3 | ||
| add limit, limit, tmp1/* Adjust the limit for the extra. */ | ||
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| lsl tmp1, tmp1, #3/* Bytes beyond alignment -> bits.*/ | ||
| neg tmp1, tmp1/* Bits to alignment -64. */ | ||
| mov tmp2, #~0 | ||
| /*mask off the non-intended bytes before the start address.*/ | ||
| CPU_BE( lsl tmp2, tmp2, tmp1 )/*Big-endian.Early bytes are at MSB*/ | ||
| /* Little-endian. Early bytes are at LSB. */ | ||
| CPU_LE( lsr tmp2, tmp2, tmp1 ) | ||
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| orr data1, data1, tmp2 | ||
| orr data2, data2, tmp2 | ||
| b .Lstart_realigned | ||
|
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| /*src1 and src2 have different alignment offset.*/ | ||
| .Lmisaligned8: | ||
| cmp limit, #8 | ||
| b.lo .Ltiny8proc /*limit < 8: compare byte by byte*/ | ||
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| and tmp1, src1, #7 | ||
| neg tmp1, tmp1 | ||
| add tmp1, tmp1, #8/*valid length in the first 8 bytes of src1*/ | ||
| and tmp2, src2, #7 | ||
| neg tmp2, tmp2 | ||
| add tmp2, tmp2, #8/*valid length in the first 8 bytes of src2*/ | ||
| subs tmp3, tmp1, tmp2 | ||
| csel pos, tmp1, tmp2, hi /*Choose the maximum.*/ | ||
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| sub limit, limit, pos | ||
| /*compare the proceeding bytes in the first 8 byte segment.*/ | ||
| .Ltinycmp: | ||
| ldrb data1w, [src1], #1 | ||
| ldrb data2w, [src2], #1 | ||
| subs pos, pos, #1 | ||
| ccmp data1w, data2w, #0, ne /* NZCV = 0b0000. */ | ||
| b.eq .Ltinycmp | ||
| cbnz pos, 1f /*diff occurred before the last byte.*/ | ||
| #define data1 x3 | ||
| #define data1w w3 | ||
| #define data2 x4 | ||
| #define data2w w4 | ||
| #define tmp1 x5 | ||
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| /* Small inputs of less than 8 bytes are handled separately. This allows the | ||
| main code to be sped up using unaligned loads since there are now at least | ||
| 8 bytes to be compared. If the first 8 bytes are equal, align src1. | ||
| This ensures each iteration does at most one unaligned access even if both | ||
| src1 and src2 are unaligned, and mutually aligned inputs behave as if | ||
| aligned. After the main loop, process the last 8 bytes using unaligned | ||
| accesses. */ | ||
|
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||
| .p2align 6 | ||
| WEAK(memcmp) | ||
| subs limit, limit, 8 | ||
| b.lo .Lless8 | ||
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| /* Limit >= 8, so check first 8 bytes using unaligned loads. */ | ||
| ldr data1, [src1], 8 | ||
| ldr data2, [src2], 8 | ||
| and tmp1, src1, 7 | ||
| add limit, limit, tmp1 | ||
| cmp data1, data2 | ||
| bne .Lreturn | ||
|
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||
| /* Align src1 and adjust src2 with bytes not yet done. */ | ||
| sub src1, src1, tmp1 | ||
| sub src2, src2, tmp1 | ||
|
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| subs limit, limit, 8 | ||
| b.ls .Llast_bytes | ||
|
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| /* Loop performing 8 bytes per iteration using aligned src1. | ||
| Limit is pre-decremented by 8 and must be larger than zero. | ||
| Exit if <= 8 bytes left to do or if the data is not equal. */ | ||
| .p2align 4 | ||
| .Lloop8: | ||
| ldr data1, [src1], 8 | ||
| ldr data2, [src2], 8 | ||
| subs limit, limit, 8 | ||
| ccmp data1, data2, 0, hi /* NZCV = 0b0000. */ | ||
| b.eq .Lloop8 | ||
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| cmp data1, data2 | ||
| bne .Lreturn | ||
|
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| /* Compare last 1-8 bytes using unaligned access. */ | ||
| .Llast_bytes: | ||
| ldr data1, [src1, limit] | ||
| ldr data2, [src2, limit] | ||
|
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| /* Compare data bytes and set return value to 0, -1 or 1. */ | ||
| .Lreturn: | ||
| #ifndef __AARCH64EB__ | ||
| rev data1, data1 | ||
| rev data2, data2 | ||
| #endif | ||
| cmp data1, data2 | ||
| .Lret_eq: | ||
| cset result, ne | ||
| cneg result, result, lo | ||
| ret | ||
|
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||
| .p2align 4 | ||
| /* Compare up to 8 bytes. Limit is [-8..-1]. */ | ||
| .Lless8: | ||
| adds limit, limit, 4 | ||
| b.lo .Lless4 | ||
| ldr data1w, [src1], 4 | ||
| ldr data2w, [src2], 4 | ||
| cmp data1w, data2w | ||
| b.eq .Lstart_align | ||
| 1: | ||
| sub result, data1, data2 | ||
| ret | ||
|
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||
| .Lstart_align: | ||
| lsr limit_wd, limit, #3 | ||
| cbz limit_wd, .Lremain8 | ||
|
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| ands xzr, src1, #7 | ||
| b.eq .Lrecal_offset | ||
| /*process more leading bytes to make src1 aligned...*/ | ||
| add src1, src1, tmp3 /*backwards src1 to alignment boundary*/ | ||
| add src2, src2, tmp3 | ||
| sub limit, limit, tmp3 | ||
| lsr limit_wd, limit, #3 | ||
| cbz limit_wd, .Lremain8 | ||
| /*load 8 bytes from aligned SRC1..*/ | ||
| ldr data1, [src1], #8 | ||
| ldr data2, [src2], #8 | ||
|
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| subs limit_wd, limit_wd, #1 | ||
| eor diff, data1, data2 /*Non-zero if differences found.*/ | ||
| csinv endloop, diff, xzr, ne | ||
| cbnz endloop, .Lunequal_proc | ||
| /*How far is the current SRC2 from the alignment boundary...*/ | ||
| and tmp3, tmp3, #7 | ||
|
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| .Lrecal_offset:/*src1 is aligned now..*/ | ||
| neg pos, tmp3 | ||
| .Lloopcmp_proc: | ||
| /* | ||
| * Divide the eight bytes into two parts. First,backwards the src2 | ||
| * to an alignment boundary,load eight bytes and compare from | ||
| * the SRC2 alignment boundary. If all 8 bytes are equal,then start | ||
| * the second part's comparison. Otherwise finish the comparison. | ||
| * This special handle can garantee all the accesses are in the | ||
| * thread/task space in avoid to overrange access. | ||
| */ | ||
| ldr data1, [src1,pos] | ||
| ldr data2, [src2,pos] | ||
| eor diff, data1, data2 /* Non-zero if differences found. */ | ||
| cbnz diff, .Lnot_limit | ||
|
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| /*The second part process*/ | ||
| ldr data1, [src1], #8 | ||
| ldr data2, [src2], #8 | ||
| eor diff, data1, data2 /* Non-zero if differences found. */ | ||
| subs limit_wd, limit_wd, #1 | ||
| csinv endloop, diff, xzr, ne/*if limit_wd is 0,will finish the cmp*/ | ||
| cbz endloop, .Lloopcmp_proc | ||
| .Lunequal_proc: | ||
| cbz diff, .Lremain8 | ||
|
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| /* There is difference occurred in the latest comparison. */ | ||
| .Lnot_limit: | ||
| /* | ||
| * For little endian,reverse the low significant equal bits into MSB,then | ||
| * following CLZ can find how many equal bits exist. | ||
| */ | ||
| CPU_LE( rev diff, diff ) | ||
| CPU_LE( rev data1, data1 ) | ||
| CPU_LE( rev data2, data2 ) | ||
|
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| /* | ||
| * The MS-non-zero bit of DIFF marks either the first bit | ||
| * that is different, or the end of the significant data. | ||
| * Shifting left now will bring the critical information into the | ||
| * top bits. | ||
| */ | ||
| clz pos, diff | ||
| lsl data1, data1, pos | ||
| lsl data2, data2, pos | ||
| /* | ||
| * We need to zero-extend (char is unsigned) the value and then | ||
| * perform a signed subtraction. | ||
| */ | ||
| lsr data1, data1, #56 | ||
| sub result, data1, data2, lsr #56 | ||
| ret | ||
|
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| .Lremain8: | ||
| /* Limit % 8 == 0 =>. all data are equal.*/ | ||
| ands limit, limit, #7 | ||
| b.eq .Lret0 | ||
|
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| .Ltiny8proc: | ||
| ldrb data1w, [src1], #1 | ||
| ldrb data2w, [src2], #1 | ||
| subs limit, limit, #1 | ||
|
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| ccmp data1w, data2w, #0, ne /* NZCV = 0b0000. */ | ||
| b.eq .Ltiny8proc | ||
| sub result, data1, data2 | ||
| ret | ||
| .Lret0: | ||
| mov result, #0 | ||
| b.ne .Lreturn | ||
| sub limit, limit, 4 | ||
| .Lless4: | ||
| adds limit, limit, 4 | ||
| beq .Lret_eq | ||
| .Lbyte_loop: | ||
| ldrb data1w, [src1], 1 | ||
| ldrb data2w, [src2], 1 | ||
| subs limit, limit, 1 | ||
| ccmp data1w, data2w, 0, ne /* NZCV = 0b0000. */ | ||
| b.eq .Lbyte_loop | ||
| sub result, data1w, data2w | ||
| ret | ||
| SYM_FUNC_END_PI(memcmp) | ||
| EXPORT_SYMBOL_NOKASAN(memcmp) | ||
| ENDPIPROC(memcmp) |