1/* Copyright (C) 1996-2022 Free Software Foundation, Inc. 2 This file is part of the GNU C Library. 3 4 The GNU C Library is free software; you can redistribute it and/or 5 modify it under the terms of the GNU Lesser General Public 6 License as published by the Free Software Foundation; either 7 version 2.1 of the License, or (at your option) any later version. 8 9 The GNU C Library is distributed in the hope that it will be useful, 10 but WITHOUT ANY WARRANTY; without even the implied warranty of 11 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU 12 Lesser General Public License for more details. 13 14 You should have received a copy of the GNU Lesser General Public 15 License along with the GNU C Library. If not, see 16 <https://www.gnu.org/licenses/>. */ 17 18/* Bytewise compare two null-terminated strings. */ 19 20#include <sysdep.h> 21 22 .set noat 23 .set noreorder 24 25 .text 26 27ENTRY(strcmp) 28#ifdef PROF 29 ldgp gp, 0(pv) 30 lda AT, _mcount 31 jmp AT, (AT), _mcount 32 .prologue 1 33#else 34 .prologue 0 35#endif 36 37 ldq_u t0, 0(a0) # e0 : give cache time to catch up 38 xor a0, a1, t2 # .. e1 : are s1 and s2 co-aligned? 39 ldq_u t1, 0(a1) # e0 : 40 and t2, 7, t2 # .. e1 : 41 lda t3, -1 # e0 : 42 bne t2, $unaligned # .. e1 : 43 44 /* On entry to this basic block: 45 t0 == the first destination word for masking back in 46 t1 == the first source word. 47 t3 == -1. */ 48 49$aligned: 50 mskqh t3, a0, t3 # e0 : 51 nop # .. e1 : 52 ornot t1, t3, t1 # e0 : 53 ornot t0, t3, t0 # .. e1 : 54 cmpbge zero, t1, t7 # e0 : bits set iff null found 55 bne t7, $eos # e1 (zdb) 56 57 /* Aligned compare main loop. 58 On entry to this basic block: 59 t0 == an s1 word. 60 t1 == an s2 word not containing a null. */ 61 62$a_loop: 63 xor t0, t1, t2 # e0 : 64 bne t2, $wordcmp # .. e1 (zdb) 65 ldq_u t1, 8(a1) # e0 : 66 ldq_u t0, 8(a0) # .. e1 : 67 addq a1, 8, a1 # e0 : 68 addq a0, 8, a0 # .. e1 : 69 cmpbge zero, t1, t7 # e0 : 70 beq t7, $a_loop # .. e1 (zdb) 71 br $eos # e1 : 72 73 /* The two strings are not co-aligned. Align s1 and cope. */ 74 75$unaligned: 76 and a0, 7, t4 # e0 : find s1 misalignment 77 and a1, 7, t5 # .. e1 : find s2 misalignment 78 subq a1, t4, a1 # e0 : 79 80 /* If s2 misalignment is larger than s2 misalignment, we need 81 extra startup checks to avoid SEGV. */ 82 83 cmplt t4, t5, t8 # .. e1 : 84 beq t8, $u_head # e1 : 85 86 mskqh t3, t5, t3 # e0 : 87 ornot t1, t3, t3 # e0 : 88 cmpbge zero, t3, t7 # e1 : is there a zero? 89 beq t7, $u_head # e1 : 90 91 /* We've found a zero in the first partial word of s2. Align 92 our current s1 and s2 words and compare what we've got. */ 93 94 extql t1, t5, t1 # e0 : 95 extql t0, a0, t0 # e0 : 96 cmpbge zero, t1, t7 # .. e1 : find that zero again 97 br $eos # e1 : and finish up 98 99 .align 3 100$u_head: 101 /* We know just enough now to be able to assemble the first 102 full word of s2. We can still find a zero at the end of it. 103 104 On entry to this basic block: 105 t0 == first word of s1 106 t1 == first partial word of s2. */ 107 108 ldq_u t2, 8(a1) # e0 : load second partial s2 word 109 lda t3, -1 # .. e1 : create leading garbage mask 110 extql t1, a1, t1 # e0 : create first s2 word 111 mskqh t3, a0, t3 # e0 : 112 extqh t2, a1, t4 # e0 : 113 ornot t0, t3, t0 # .. e1 : kill s1 garbage 114 or t1, t4, t1 # e0 : s2 word now complete 115 cmpbge zero, t0, t7 # .. e1 : find zero in first s1 word 116 ornot t1, t3, t1 # e0 : kill s2 garbage 117 lda t3, -1 # .. e1 : 118 mskql t3, a1, t3 # e0 : mask for s2[1] bits we have seen 119 bne t7, $eos # .. e1 : 120 xor t0, t1, t4 # e0 : compare aligned words 121 bne t4, $wordcmp # .. e1 (zdb) 122 or t2, t3, t3 # e0 : 123 cmpbge zero, t3, t7 # e1 : 124 bne t7, $u_final # e1 : 125 126 /* Unaligned copy main loop. In order to avoid reading too much, 127 the loop is structured to detect zeros in aligned words from s2. 128 This has, unfortunately, effectively pulled half of a loop 129 iteration out into the head and half into the tail, but it does 130 prevent nastiness from accumulating in the very thing we want 131 to run as fast as possible. 132 133 On entry to this basic block: 134 t2 == the unshifted low-bits from the next s2 word. */ 135 136 .align 3 137$u_loop: 138 extql t2, a1, t3 # e0 : 139 ldq_u t2, 16(a1) # .. e1 : load next s2 high bits 140 ldq_u t0, 8(a0) # e0 : load next s1 word 141 addq a1, 8, a1 # .. e1 : 142 addq a0, 8, a0 # e0 : 143 nop # .. e1 : 144 extqh t2, a1, t1 # e0 : 145 cmpbge zero, t0, t7 # .. e1 : find zero in current s1 word 146 or t1, t3, t1 # e0 : 147 bne t7, $eos # .. e1 : 148 xor t0, t1, t4 # e0 : compare the words 149 bne t4, $wordcmp # .. e1 (zdb) 150 cmpbge zero, t2, t4 # e0 : find zero in next low bits 151 beq t4, $u_loop # .. e1 (zdb) 152 153 /* We've found a zero in the low bits of the last s2 word. Get 154 the next s1 word and align them. */ 155$u_final: 156 ldq_u t0, 8(a0) # e1 : 157 extql t2, a1, t1 # .. e0 : 158 cmpbge zero, t1, t7 # e0 : 159 160 /* We've found a zero somewhere in a word we just read. 161 On entry to this basic block: 162 t0 == s1 word 163 t1 == s2 word 164 t7 == cmpbge mask containing the zero. */ 165 166 .align 3 167$eos: 168 negq t7, t6 # e0 : create bytemask of valid data 169 and t6, t7, t8 # e1 : 170 subq t8, 1, t6 # e0 : 171 or t6, t8, t7 # e1 : 172 zapnot t0, t7, t0 # e0 : kill the garbage 173 zapnot t1, t7, t1 # .. e1 : 174 xor t0, t1, v0 # e0 : and compare 175 beq v0, $done # .. e1 : 176 177 /* Here we have two differing co-aligned words in t0 & t1. 178 Bytewise compare them and return (t0 > t1 ? 1 : -1). */ 179$wordcmp: 180 cmpbge t0, t1, t2 # e0 : comparison yields bit mask of ge 181 cmpbge t1, t0, t3 # .. e1 : 182 xor t2, t3, t0 # e0 : bits set iff t0/t1 bytes differ 183 negq t0, t1 # e1 : clear all but least bit 184 and t0, t1, t0 # e0 : 185 lda v0, -1 # .. e1 : 186 and t0, t2, t1 # e0 : was bit set in t0 > t1? 187 cmovne t1, 1, v0 # .. e1 (zdb) 188 189$done: 190 ret # e1 : 191 192 END(strcmp) 193libc_hidden_builtin_def (strcmp) 194