1/* Copyright (c) 2012, Linaro Limited 2 All rights reserved. 3 4 Redistribution and use in source and binary forms, with or without 5 modification, are permitted provided that the following conditions are met: 6 * Redistributions of source code must retain the above copyright 7 notice, this list of conditions and the following disclaimer. 8 * Redistributions in binary form must reproduce the above copyright 9 notice, this list of conditions and the following disclaimer in the 10 documentation and/or other materials provided with the distribution. 11 * Neither the name of the Linaro nor the 12 names of its contributors may be used to endorse or promote products 13 derived from this software without specific prior written permission. 14 15 THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS 16 "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT 17 LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR 18 A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT 19 HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, 20 SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT 21 LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, 22 DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY 23 THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT 24 (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE 25 OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. */ 26 27/* Assumptions: 28 * 29 * ARMv8-a, AArch64 30 */ 31 32 .macro def_fn f p2align=0 33 .text 34 .p2align \p2align 35 .global \f 36 .type \f, %function 37\f: 38 .endm 39 40#define REP8_01 0x0101010101010101 41#define REP8_7f 0x7f7f7f7f7f7f7f7f 42#define REP8_80 0x8080808080808080 43 44/* Parameters and result. */ 45#define src1 x0 46#define src2 x1 47#define result x0 48 49/* Internal variables. */ 50#define data1 x2 51#define data1w w2 52#define data2 x3 53#define data2w w3 54#define has_nul x4 55#define diff x5 56#define syndrome x6 57#define tmp1 x7 58#define tmp2 x8 59#define tmp3 x9 60#define zeroones x10 61#define pos x11 62 63 /* Start of performance-critical section -- one 64B cache line. */ 64def_fn strcmp p2align=6 65 eor tmp1, src1, src2 66 mov zeroones, #REP8_01 67 tst tmp1, #7 68 b.ne .Lmisaligned8 69 ands tmp1, src1, #7 70 b.ne .Lmutual_align 71 /* NUL detection works on the principle that (X - 1) & (~X) & 0x80 72 (=> (X - 1) & ~(X | 0x7f)) is non-zero iff a byte is zero, and 73 can be done in parallel across the entire word. */ 74.Lloop_aligned: 75 ldr data1, [src1], #8 76 ldr data2, [src2], #8 77.Lstart_realigned: 78 sub tmp1, data1, zeroones 79 orr tmp2, data1, #REP8_7f 80 eor diff, data1, data2 /* Non-zero if differences found. */ 81 bic has_nul, tmp1, tmp2 /* Non-zero if NUL terminator. */ 82 orr syndrome, diff, has_nul 83 cbz syndrome, .Lloop_aligned 84 /* End of performance-critical section -- one 64B cache line. */ 85 86#ifndef __AARCH64EB__ 87 rev syndrome, syndrome 88 rev data1, data1 89 /* The MS-non-zero bit of the syndrome marks either the first bit 90 that is different, or the top bit of the first zero byte. 91 Shifting left now will bring the critical information into the 92 top bits. */ 93 clz pos, syndrome 94 rev data2, data2 95 lsl data1, data1, pos 96 lsl data2, data2, pos 97 /* But we need to zero-extend (char is unsigned) the value and then 98 perform a signed 32-bit subtraction. */ 99 lsr data1, data1, #56 100 sub result, data1, data2, lsr #56 101 ret 102#else 103 /* For big-endian we cannot use the trick with the syndrome value 104 as carry-propagation can corrupt the upper bits if the trailing 105 bytes in the string contain 0x01. */ 106 /* However, if there is no NUL byte in the dword, we can generate 107 the result directly. We can't just subtract the bytes as the 108 MSB might be significant. */ 109 cbnz has_nul, 1f 110 cmp data1, data2 111 cset result, ne 112 cneg result, result, lo 113 ret 1141: 115 /* Re-compute the NUL-byte detection, using a byte-reversed value. */ 116 rev tmp3, data1 117 sub tmp1, tmp3, zeroones 118 orr tmp2, tmp3, #REP8_7f 119 bic has_nul, tmp1, tmp2 120 rev has_nul, has_nul 121 orr syndrome, diff, has_nul 122 clz pos, syndrome 123 /* The MS-non-zero bit of the syndrome marks either the first bit 124 that is different, or the top bit of the first zero byte. 125 Shifting left now will bring the critical information into the 126 top bits. */ 127 lsl data1, data1, pos 128 lsl data2, data2, pos 129 /* But we need to zero-extend (char is unsigned) the value and then 130 perform a signed 32-bit subtraction. */ 131 lsr data1, data1, #56 132 sub result, data1, data2, lsr #56 133 ret 134#endif 135 136.Lmutual_align: 137 /* Sources are mutually aligned, but are not currently at an 138 alignment boundary. Round down the addresses and then mask off 139 the bytes that preceed the start point. */ 140 bic src1, src1, #7 141 bic src2, src2, #7 142 lsl tmp1, tmp1, #3 /* Bytes beyond alignment -> bits. */ 143 ldr data1, [src1], #8 144 neg tmp1, tmp1 /* Bits to alignment -64. */ 145 ldr data2, [src2], #8 146 mov tmp2, #~0 147#ifdef __AARCH64EB__ 148 /* Big-endian. Early bytes are at MSB. */ 149 lsl tmp2, tmp2, tmp1 /* Shift (tmp1 & 63). */ 150#else 151 /* Little-endian. Early bytes are at LSB. */ 152 lsr tmp2, tmp2, tmp1 /* Shift (tmp1 & 63). */ 153#endif 154 orr data1, data1, tmp2 155 orr data2, data2, tmp2 156 b .Lstart_realigned 157 158.Lmisaligned8: 159 /* We can do better than this. */ 160 ldrb data1w, [src1], #1 161 ldrb data2w, [src2], #1 162 cmp data1w, #1 163 ccmp data1w, data2w, #0, cs /* NZCV = 0b0000. */ 164 b.eq .Lmisaligned8 165 sub result, data1, data2 166 ret 167