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299 lines
8.2 KiB
299 lines
8.2 KiB
/* SPDX-License-Identifier: GPL-2.0-only */ |
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/* |
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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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* 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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#include <linux/linkage.h> |
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#include <asm/assembler.h> |
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/* |
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* compare two strings |
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* |
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* Parameters: |
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* x0 - const string 1 pointer |
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* x1 - const string 2 pointer |
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* x2 - the maximal length to be compared |
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* Returns: |
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* x0 - an integer less than, equal to, or greater than zero if s1 is found, |
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* respectively, to be less than, to match, or be greater than s2. |
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*/ |
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#define REP8_01 0x0101010101010101 |
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#define REP8_7f 0x7f7f7f7f7f7f7f7f |
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#define REP8_80 0x8080808080808080 |
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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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syndrome .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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zeroones .req x11 |
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pos .req x12 |
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limit_wd .req x13 |
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mask .req x14 |
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endloop .req x15 |
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SYM_FUNC_START_WEAK_PI(strncmp) |
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cbz limit, .Lret0 |
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eor tmp1, src1, src2 |
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mov zeroones, #REP8_01 |
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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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/* Calculate the number of full and partial words -1. */ |
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/* |
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* when limit is mulitply of 8, if not sub 1, |
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* the judgement of last dword will wrong. |
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*/ |
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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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* NUL detection works on the principle that (X - 1) & (~X) & 0x80 |
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* (=> (X - 1) & ~(X | 0x7f)) is non-zero iff a byte is zero, and |
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* can be done in parallel across the entire word. |
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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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sub tmp1, data1, zeroones |
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orr tmp2, data1, #REP8_7f |
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eor diff, data1, data2 /* Non-zero if differences found. */ |
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csinv endloop, diff, xzr, pl /* Last Dword or differences.*/ |
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bics has_nul, tmp1, tmp2 /* Non-zero if NUL terminator. */ |
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ccmp endloop, #0, #0, eq |
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b.eq .Lloop_aligned |
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/*Not reached the limit, must have found the end or a diff. */ |
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tbz limit_wd, #63, .Lnot_limit |
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/* Limit % 8 == 0 => all bytes significant. */ |
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ands limit, limit, #7 |
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b.eq .Lnot_limit |
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lsl limit, limit, #3 /* Bits -> bytes. */ |
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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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/* Make sure that the NUL byte is marked in the syndrome. */ |
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orr has_nul, has_nul, mask |
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.Lnot_limit: |
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orr syndrome, diff, has_nul |
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b .Lcal_cmpresult |
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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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* We also need to adjust the limit calculations, but without |
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* overflowing if the limit is near ULONG_MAX. |
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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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neg tmp3, tmp1, lsl #3 /* 64 - bits(bytes beyond align). */ |
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ldr data2, [src2], #8 |
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mov tmp2, #~0 |
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sub limit_wd, limit, #1 /* limit != 0, so no underflow. */ |
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/* Big-endian. Early bytes are at MSB. */ |
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CPU_BE( lsl tmp2, tmp2, tmp3 ) /* Shift (tmp1 & 63). */ |
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/* Little-endian. Early bytes are at LSB. */ |
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CPU_LE( lsr tmp2, tmp2, tmp3 ) /* Shift (tmp1 & 63). */ |
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and tmp3, limit_wd, #7 |
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lsr limit_wd, limit_wd, #3 |
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/* Adjust the limit. Only low 3 bits used, so overflow irrelevant.*/ |
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add limit, limit, tmp1 |
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add tmp3, tmp3, tmp1 |
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orr data1, data1, tmp2 |
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orr data2, data2, tmp2 |
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add limit_wd, limit_wd, tmp3, lsr #3 |
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b .Lstart_realigned |
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/*when src1 offset is not equal to src2 offset...*/ |
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.Lmisaligned8: |
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cmp limit, #8 |
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b.lo .Ltiny8proc /*limit < 8... */ |
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/* |
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* Get the align offset length to compare per byte first. |
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* After this process, one string's address will be aligned.*/ |
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and tmp1, src1, #7 |
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neg tmp1, tmp1 |
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add tmp1, tmp1, #8 |
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and tmp2, src2, #7 |
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neg tmp2, tmp2 |
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add tmp2, tmp2, #8 |
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subs tmp3, tmp1, tmp2 |
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csel pos, tmp1, tmp2, hi /*Choose the maximum. */ |
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/* |
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* Here, limit is not less than 8, so directly run .Ltinycmp |
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* without checking the limit.*/ |
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sub limit, limit, pos |
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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, #1, #0, ne /* NZCV = 0b0000. */ |
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ccmp data1w, data2w, #0, cs /* NZCV = 0b0000. */ |
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b.eq .Ltinycmp |
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cbnz pos, 1f /*find the null or unequal...*/ |
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cmp data1w, #1 |
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ccmp data1w, data2w, #0, cs |
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b.eq .Lstart_align /*the last bytes are equal....*/ |
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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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/*process more leading bytes to make str1 aligned...*/ |
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ands xzr, src1, #7 |
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b.eq .Lrecal_offset |
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add src1, src1, tmp3 /*tmp3 is positive in this branch.*/ |
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add src2, src2, tmp3 |
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ldr data1, [src1], #8 |
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ldr data2, [src2], #8 |
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sub limit, limit, tmp3 |
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lsr limit_wd, limit, #3 |
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subs limit_wd, limit_wd, #1 |
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sub tmp1, data1, zeroones |
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orr tmp2, data1, #REP8_7f |
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eor diff, data1, data2 /* Non-zero if differences found. */ |
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csinv endloop, diff, xzr, ne/*if limit_wd is 0,will finish the cmp*/ |
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bics has_nul, tmp1, tmp2 |
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ccmp endloop, #0, #0, eq /*has_null is ZERO: no null byte*/ |
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b.ne .Lunequal_proc |
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/*How far is the current str2 from the alignment boundary...*/ |
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and tmp3, tmp3, #7 |
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.Lrecal_offset: |
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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 from the SRC2 alignment |
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* boundary,then compare with the relative bytes from SRC1. |
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* If all 8 bytes are equal,then start the second part's comparison. |
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* 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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sub tmp1, data1, zeroones |
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orr tmp2, data1, #REP8_7f |
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bics has_nul, tmp1, tmp2 /* Non-zero if NUL terminator. */ |
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eor diff, data1, data2 /* Non-zero if differences found. */ |
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csinv endloop, diff, xzr, eq |
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cbnz endloop, .Lunequal_proc |
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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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subs limit_wd, limit_wd, #1 |
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sub tmp1, data1, zeroones |
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orr tmp2, data1, #REP8_7f |
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eor diff, data1, data2 /* Non-zero if differences found. */ |
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csinv endloop, diff, xzr, ne/*if limit_wd is 0,will finish the cmp*/ |
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bics has_nul, tmp1, tmp2 |
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ccmp endloop, #0, #0, eq /*has_null is ZERO: no null byte*/ |
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b.eq .Lloopcmp_proc |
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.Lunequal_proc: |
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orr syndrome, diff, has_nul |
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cbz syndrome, .Lremain8 |
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.Lcal_cmpresult: |
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/* |
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* reversed the byte-order as big-endian,then CLZ can find the most |
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* significant zero bits. |
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*/ |
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CPU_LE( rev syndrome, syndrome ) |
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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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* For big-endian we cannot use the trick with the syndrome value |
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* as carry-propagation can corrupt the upper bits if the trailing |
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* bytes in the string contain 0x01. |
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* However, if there is no NUL byte in the dword, we can generate |
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* the result directly. We can't just subtract the bytes as the |
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* MSB might be significant. |
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*/ |
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CPU_BE( cbnz has_nul, 1f ) |
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CPU_BE( cmp data1, data2 ) |
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CPU_BE( cset result, ne ) |
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CPU_BE( cneg result, result, lo ) |
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CPU_BE( ret ) |
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CPU_BE( 1: ) |
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/* Re-compute the NUL-byte detection, using a byte-reversed value.*/ |
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CPU_BE( rev tmp3, data1 ) |
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CPU_BE( sub tmp1, tmp3, zeroones ) |
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CPU_BE( orr tmp2, tmp3, #REP8_7f ) |
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CPU_BE( bic has_nul, tmp1, tmp2 ) |
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CPU_BE( rev has_nul, has_nul ) |
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CPU_BE( orr syndrome, diff, has_nul ) |
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/* |
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* The MS-non-zero bit of the syndrome marks either the first bit |
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* that is different, or the top bit of the first zero byte. |
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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, syndrome |
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lsl data1, data1, pos |
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lsl data2, data2, pos |
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/* |
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* But we need to zero-extend (char is unsigned) the value and then |
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* perform a signed 32-bit 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 bytes significant. */ |
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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, #1, #0, ne /* NZCV = 0b0000. */ |
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ccmp data1w, data2w, #0, cs /* 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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SYM_FUNC_END_PI(strncmp) |
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EXPORT_SYMBOL_NOKASAN(strncmp)
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