1/* Optimized strnlen implementation for PowerPC32/POWER7 using cmpb insn. 2 Copyright (C) 2010-2022 Free Software Foundation, Inc. 3 This file is part of the GNU C Library. 4 5 The GNU C Library is free software; you can redistribute it and/or 6 modify it under the terms of the GNU Lesser General Public 7 License as published by the Free Software Foundation; either 8 version 2.1 of the License, or (at your option) any later version. 9 10 The GNU C Library is distributed in the hope that it will be useful, 11 but WITHOUT ANY WARRANTY; without even the implied warranty of 12 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU 13 Lesser General Public License for more details. 14 15 You should have received a copy of the GNU Lesser General Public 16 License along with the GNU C Library; if not, see 17 <https://www.gnu.org/licenses/>. */ 18 19#include <sysdep.h> 20 21/* int [r3] strnlen (char *s [r3], int size [r4]) */ 22 .machine power7 23ENTRY (__strnlen) 24 CALL_MCOUNT 25 dcbt 0,r3 26 clrrwi r8,r3,2 /* Align the address to word boundary. */ 27 add r7,r3,r4 /* Calculate the last acceptable address. */ 28 cmplwi r4,16 29 li r0,0 /* Word with null chars. */ 30 addi r7,r7,-1 31 ble L(small_range) 32 33 rlwinm r6,r3,3,27,28 /* Calculate padding. */ 34 lwz r12,0(r8) /* Load word from memory. */ 35 cmpb r10,r12,r0 /* Check for null bytes in DWORD1. */ 36#ifdef __LITTLE_ENDIAN__ 37 srw r10,r10,r6 38 slw r10,r10,r6 39#else 40 slw r10,r10,r6 41 srw r10,r10,r6 42#endif 43 cmplwi cr7,r10,0 /* If r10 == 0, no null's have been found. */ 44 bne cr7,L(done) 45 46 clrrwi r7,r7,2 /* Address of last word. */ 47 mtcrf 0x01,r8 48 /* Are we now aligned to a doubleword boundary? If so, skip to 49 the main loop. Otherwise, go through the alignment code. */ 50 51 bt 29,L(loop_setup) 52 53 /* Handle WORD2 of pair. */ 54 lwzu r12,4(r8) 55 cmpb r10,r12,r0 56 cmplwi cr7,r10,0 57 bne cr7,L(done) 58 59L(loop_setup): 60 /* The last word we want to read in the loop below is the one 61 containing the last byte of the string, ie. the word at 62 (s + size - 1) & ~3, or r7. The first word read is at 63 r8 + 4, we read 2 * cnt words, so the last word read will 64 be at r8 + 4 + 8 * cnt - 4. Solving for cnt gives 65 cnt = (r7 - r8) / 8 */ 66 sub r5,r7,r8 67 srwi r6,r5,3 /* Number of loop iterations. */ 68 mtctr r6 /* Setup the counter. */ 69 70 /* Main loop to look for the null byte in the string. Since 71 it's a small loop (< 8 instructions), align it to 32-bytes. */ 72 .p2align 5 73L(loop): 74 /* Load two words, compare and merge in a 75 single register for speed. This is an attempt 76 to speed up the null-checking process for bigger strings. */ 77 78 lwz r12,4(r8) 79 lwzu r11,8(r8) 80 cmpb r10,r12,r0 81 cmpb r9,r11,r0 82 or r5,r9,r10 /* Merge everything in one word. */ 83 cmplwi cr7,r5,0 84 bne cr7,L(found) 85 bdnz L(loop) 86 87 /* We may have one more word to read. */ 88 cmplw cr6,r8,r7 89 beq cr6,L(end_max) 90 91 lwzu r12,4(r8) 92 cmpb r10,r12,r0 93 cmplwi cr6,r10,0 94 bne cr6,L(done) 95 96L(end_max): 97 mr r3,r4 98 blr 99 100 /* OK, one (or both) of the words contains a null byte. Check 101 the first word and decrement the address in case the first 102 word really contains a null byte. */ 103 .align 4 104L(found): 105 cmplwi cr6,r10,0 106 addi r8,r8,-4 107 bne cr6,L(done) 108 109 /* The null byte must be in the second word. Adjust the address 110 again and move the result of cmpb to r10 so we can calculate the 111 length. */ 112 113 mr r10,r9 114 addi r8,r8,4 115 116 /* r10 has the output of the cmpb instruction, that is, it contains 117 0xff in the same position as the null byte in the original 118 word from the string. Use that to calculate the length. 119 We need to make sure the null char is *before* the end of the 120 range. */ 121L(done): 122#ifdef __LITTLE_ENDIAN__ 123 addi r0,r10,-1 124 andc r0,r0,r10 125 popcntw r0,r0 126#else 127 cntlzw r0,r10 /* Count leading zeros before the match. */ 128#endif 129 sub r3,r8,r3 130 srwi r0,r0,3 /* Convert leading/trailing zeros to bytes. */ 131 add r3,r3,r0 /* Length until the match. */ 132 cmplw r3,r4 133 blelr 134 mr r3,r4 135 blr 136 137/* Deals with size <= 16. */ 138 .align 4 139L(small_range): 140 cmplwi r4,0 141 beq L(end_max) 142 143 clrrwi r7,r7,2 /* Address of last word. */ 144 145 rlwinm r6,r3,3,27,28 /* Calculate padding. */ 146 lwz r12,0(r8) /* Load word from memory. */ 147 cmpb r10,r12,r0 /* Check for null bytes in WORD1. */ 148#ifdef __LITTLE_ENDIAN__ 149 srw r10,r10,r6 150 slw r10,r10,r6 151#else 152 slw r10,r10,r6 153 srw r10,r10,r6 154#endif 155 cmplwi cr7,r10,0 156 bne cr7,L(done) 157 158 cmplw r8,r7 159 beq L(end_max) 160 161 .p2align 5 162L(loop_small): 163 lwzu r12,4(r8) 164 cmpb r10,r12,r0 165 cmplwi cr6,r10,0 166 bne cr6,L(done) 167 cmplw r8,r7 168 bne L(loop_small) 169 mr r3,r4 170 blr 171 172END (__strnlen) 173libc_hidden_def (__strnlen) 174weak_alias (__strnlen, strnlen) 175libc_hidden_builtin_def (strnlen) 176