1/* memchr (str, ch, n) -- Return pointer to first occurrence of CH in the 2 first N bytes of STR. 3 For Motorola 68000. 4 Copyright (C) 1999-2022 Free Software Foundation, Inc. 5 This file is part of the GNU C Library. 6 7 The GNU C Library is free software; you can redistribute it and/or 8 modify it under the terms of the GNU Lesser General Public 9 License as published by the Free Software Foundation; either 10 version 2.1 of the License, or (at your option) any later version. 11 12 The GNU C Library is distributed in the hope that it will be useful, 13 but WITHOUT ANY WARRANTY; without even the implied warranty of 14 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU 15 Lesser General Public License for more details. 16 17 You should have received a copy of the GNU Lesser General Public 18 License along with the GNU C Library. If not, see 19 <https://www.gnu.org/licenses/>. */ 20 21#include <sysdep.h> 22#include "asm-syntax.h" 23 24 TEXT 25ENTRY(__memchr) 26 /* Save the callee-saved registers we use. */ 27#ifdef __mcoldfire__ 28 movel R(d2),MEM_PREDEC(sp) 29 cfi_adjust_cfa_offset (4) 30 movel R(d3),MEM_PREDEC(sp) 31 cfi_adjust_cfa_offset (4) 32 movel R(d4),MEM_PREDEC(sp) 33 cfi_adjust_cfa_offset (4) 34 cfi_rel_offset (R(d2), 8) 35 cfi_rel_offset (R(d3), 4) 36 cfi_rel_offset (R(d4), 0) 37#else 38 moveml R(d2)-R(d4),MEM_PREDEC(sp) 39 cfi_adjust_cfa_offset (3*4) 40 cfi_rel_offset (R(d2), 0) 41 cfi_rel_offset (R(d3), 4) 42 cfi_rel_offset (R(d4), 8) 43#endif 44 45 /* Get string pointer, character and length. */ 46 movel MEM_DISP(sp,16),R(a0) 47 moveb MEM_DISP(sp,23),R(d0) 48 movel MEM_DISP(sp,24),R(d4) 49 50 /* Check if at least four bytes left to search. */ 51#ifdef __mcoldfire__ 52 subql #4,R(d4) 53 bcs L(L6) 54 addql #4,R(d4) 55#else 56 moveql #4,R(d1) 57 cmpl R(d1),R(d4) 58 bcs L(L6) 59#endif 60 61 /* Distribute the character to all bytes of a longword. */ 62 movel R(d0),R(d1) 63 lsll #8,R(d1) 64 moveb R(d0),R(d1) 65 movel R(d1),R(d0) 66 swap R(d0) 67 movew R(d1),R(d0) 68 69 /* First search for the character one byte at a time until the 70 pointer is aligned to a longword boundary. */ 71 movel R(a0),R(d1) 72#ifdef __mcoldfire__ 73 andl #3,R(d1) 74#else 75 andw #3,R(d1) 76#endif 77 beq L(L1) 78 cmpb MEM(a0),R(d0) 79 beq L(L9) 80 addql #1,R(a0) 81 subql #1,R(d4) 82 beq L(L7) 83 84#ifdef __mcoldfire__ 85 subql #3,R(d1) 86#else 87 subqw #3,R(d1) 88#endif 89 beq L(L1) 90 cmpb MEM(a0),R(d0) 91 beq L(L9) 92 addql #1,R(a0) 93 subql #1,R(d4) 94 beq L(L7) 95 96#ifdef __mcoldfire__ 97 addql #1,R(d1) 98#else 99 addqw #1,R(d1) 100#endif 101 beq L(L1) 102 cmpb MEM(a0),R(d0) 103 beq L(L9) 104 addql #1,R(a0) 105 subql #1,R(d4) 106 beq L(L7) 107 108L(L1:) 109 /* Load the magic bits. Unlike the generic implementation we can 110 use the carry bit as the fourth hole. */ 111 movel #0xfefefeff,R(d3) 112 113 /* We exit the loop if adding MAGIC_BITS to LONGWORD fails to 114 change any of the hole bits of LONGWORD. 115 116 1) Is this safe? Will it catch all the zero bytes? 117 Suppose there is a byte with all zeros. Any carry bits 118 propagating from its left will fall into the hole at its 119 least significant bit and stop. Since there will be no 120 carry from its most significant bit, the LSB of the 121 byte to the left will be unchanged, and the zero will be 122 detected. 123 124 2) Is this worthwhile? Will it ignore everything except 125 zero bytes? Suppose every byte of LONGWORD has a bit set 126 somewhere. There will be a carry into bit 8. If bit 8 127 is set, this will carry into bit 16. If bit 8 is clear, 128 one of bits 9-15 must be set, so there will be a carry 129 into bit 16. Similarly, there will be a carry into bit 130 24. If one of bits 24-31 is set, there will be a carry 131 into bit 32 (=carry flag), so all of the hole bits will 132 be changed. 133 134 3) But wait! Aren't we looking for C, not zero? 135 Good point. So what we do is XOR LONGWORD with a longword, 136 each of whose bytes is C. This turns each byte that is C 137 into a zero. */ 138 139 /* Still at least 4 bytes to search? */ 140 subql #4,R(d4) 141 bcs L(L6) 142 143L(L2:) 144 /* Get the longword in question. */ 145 movel MEM_POSTINC(a0),R(d1) 146 /* XOR with the byte we search for. */ 147 eorl R(d0),R(d1) 148 149 /* Add the magic value. We get carry bits reported for each byte 150 which is not C. */ 151 movel R(d3),R(d2) 152 addl R(d1),R(d2) 153 154 /* Check the fourth carry bit before it is clobbered by the next 155 XOR. If it is not set we have a hit. */ 156 bcc L(L8) 157 158 /* We are only interested in carry bits that change due to the 159 previous add, so remove original bits. */ 160 eorl R(d1),R(d2) 161 162 /* Now test for the other three overflow bits. 163 Set all non-carry bits. */ 164 orl R(d3),R(d2) 165 /* Add 1 to get zero if all carry bits were set. */ 166 addql #1,R(d2) 167 168 /* If we don't get zero then at least one byte of the word equals 169 C. */ 170 bne L(L8) 171 172 /* Still at least 4 bytes to search? */ 173 subql #4,R(d4) 174 bcs L(L6) 175 176 /* Get the longword in question. */ 177 movel MEM_POSTINC(a0),R(d1) 178 /* XOR with the byte we search for. */ 179 eorl R(d0),R(d1) 180 181 /* Add the magic value. We get carry bits reported for each byte 182 which is not C. */ 183 movel R(d3),R(d2) 184 addl R(d1),R(d2) 185 186 /* Check the fourth carry bit before it is clobbered by the next 187 XOR. If it is not set we have a hit. */ 188 bcc L(L8) 189 190 /* We are only interested in carry bits that change due to the 191 previous add, so remove original bits */ 192 eorl R(d1),R(d2) 193 194 /* Now test for the other three overflow bits. 195 Set all non-carry bits. */ 196 orl R(d3),R(d2) 197 /* Add 1 to get zero if all carry bits were set. */ 198 addql #1,R(d2) 199 200 /* If we don't get zero then at least one byte of the word equals 201 C. */ 202 bne L(L8) 203 204 /* Still at least 4 bytes to search? */ 205 subql #4,R(d4) 206 bcc L(L2) 207 208L(L6:) 209 /* Search one byte at a time in the remaining less than 4 bytes. */ 210#ifdef __mcoldfire__ 211 addql #4,R(d4) 212#else 213 andw #3,R(d4) 214#endif 215 beq L(L7) 216 cmpb MEM(a0),R(d0) 217 beq L(L9) 218 addql #1,R(a0) 219 220#ifdef __mcoldfire__ 221 subql #1,R(d4) 222#else 223 subqw #1,R(d4) 224#endif 225 beq L(L7) 226 cmpb MEM(a0),R(d0) 227 beq L(L9) 228 addql #1,R(a0) 229 230#ifdef __mcoldfire__ 231 subql #1,R(d4) 232#else 233 subqw #1,R(d4) 234#endif 235 beq L(L7) 236 cmpb MEM(a0),R(d0) 237 beq L(L9) 238 239L(L7:) 240 /* Return NULL. */ 241 clrl R(d0) 242 movel R(d0),R(a0) 243#ifdef __mcoldfire__ 244 movel MEM_POSTINC(sp),R(d4) 245 cfi_remember_state 246 cfi_adjust_cfa_offset (-4) 247 cfi_restore (R(d4)) 248 movel MEM_POSTINC(sp),R(d3) 249 cfi_adjust_cfa_offset (-4) 250 cfi_restore (R(d3)) 251 movel MEM_POSTINC(sp),R(d2) 252 cfi_adjust_cfa_offset (-4) 253 cfi_restore (R(d2)) 254#else 255 moveml MEM_POSTINC(sp),R(d2)-R(d4) 256 cfi_remember_state 257 cfi_adjust_cfa_offset (-3*4) 258 cfi_restore (R(d2)) 259 cfi_restore (R(d3)) 260 cfi_restore (R(d4)) 261#endif 262 rts 263 264 cfi_restore_state 265L(L8:) 266 /* We have a hit. Check to see which byte it was. First 267 compensate for the autoincrement in the loop. */ 268 subql #4,R(a0) 269 270 cmpb MEM(a0),R(d0) 271 beq L(L9) 272 addql #1,R(a0) 273 274 cmpb MEM(a0),R(d0) 275 beq L(L9) 276 addql #1,R(a0) 277 278 cmpb MEM(a0),R(d0) 279 beq L(L9) 280 addql #1,R(a0) 281 282 /* Otherwise the fourth byte must equal C. */ 283L(L9:) 284 movel R(a0),R(d0) 285#ifdef __mcoldfire__ 286 movel MEM_POSTINC(sp),R(d4) 287 cfi_adjust_cfa_offset (-4) 288 cfi_restore (R(d4)) 289 movel MEM_POSTINC(sp),R(d3) 290 cfi_adjust_cfa_offset (-4) 291 cfi_restore (R(d3)) 292 movel MEM_POSTINC(sp),R(d2) 293 cfi_adjust_cfa_offset (-4) 294 cfi_restore (R(d2)) 295#else 296 moveml MEM_POSTINC(sp),R(d2)-R(d4) 297 cfi_adjust_cfa_offset (-3*4) 298 cfi_restore (R(d2)) 299 cfi_restore (R(d3)) 300 cfi_restore (R(d4)) 301#endif 302 rts 303END(__memchr) 304 305weak_alias (__memchr, memchr) 306libc_hidden_builtin_def (memchr) 307