1/* 2 * Copyright (C) 2013 ARM Ltd. 3 * Copyright (C) 2013 Linaro. 4 * 5 * This code is based on glibc cortex strings work originally authored by Linaro 6 * and re-licensed under GPLv2 for the Linux kernel. The original code can 7 * be found @ 8 * 9 * http://bazaar.launchpad.net/~linaro-toolchain-dev/cortex-strings/trunk/ 10 * files/head:/src/aarch64/ 11 * 12 * This program is free software; you can redistribute it and/or modify 13 * it under the terms of the GNU General Public License version 2 as 14 * published by the Free Software Foundation. 15 * 16 * This program is distributed in the hope that it will be useful, 17 * but WITHOUT ANY WARRANTY; without even the implied warranty of 18 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the 19 * GNU General Public License for more details. 20 * 21 * You should have received a copy of the GNU General Public License 22 * along with this program. If not, see <http://www.gnu.org/licenses/>. 23 */ 24 25#include <linux/linkage.h> 26#include <asm/assembler.h> 27 28/* 29 * compare two strings 30 * 31 * Parameters: 32 * x0 - const string 1 pointer 33 * x1 - const string 2 pointer 34 * x2 - the maximal length to be compared 35 * Returns: 36 * x0 - an integer less than, equal to, or greater than zero if s1 is found, 37 * respectively, to be less than, to match, or be greater than s2. 38 */ 39 40#define REP8_01 0x0101010101010101 41#define REP8_7f 0x7f7f7f7f7f7f7f7f 42#define REP8_80 0x8080808080808080 43 44/* Parameters and result. */ 45src1 .req x0 46src2 .req x1 47limit .req x2 48result .req x0 49 50/* Internal variables. */ 51data1 .req x3 52data1w .req w3 53data2 .req x4 54data2w .req w4 55has_nul .req x5 56diff .req x6 57syndrome .req x7 58tmp1 .req x8 59tmp2 .req x9 60tmp3 .req x10 61zeroones .req x11 62pos .req x12 63limit_wd .req x13 64mask .req x14 65endloop .req x15 66 67ENTRY(strncmp) 68 cbz limit, .Lret0 69 eor tmp1, src1, src2 70 mov zeroones, #REP8_01 71 tst tmp1, #7 72 b.ne .Lmisaligned8 73 ands tmp1, src1, #7 74 b.ne .Lmutual_align 75 /* Calculate the number of full and partial words -1. */ 76 /* 77 * when limit is mulitply of 8, if not sub 1, 78 * the judgement of last dword will wrong. 79 */ 80 sub limit_wd, limit, #1 /* limit != 0, so no underflow. */ 81 lsr limit_wd, limit_wd, #3 /* Convert to Dwords. */ 82 83 /* 84 * NUL detection works on the principle that (X - 1) & (~X) & 0x80 85 * (=> (X - 1) & ~(X | 0x7f)) is non-zero iff a byte is zero, and 86 * can be done in parallel across the entire word. 87 */ 88.Lloop_aligned: 89 ldr data1, [src1], #8 90 ldr data2, [src2], #8 91.Lstart_realigned: 92 subs limit_wd, limit_wd, #1 93 sub tmp1, data1, zeroones 94 orr tmp2, data1, #REP8_7f 95 eor diff, data1, data2 /* Non-zero if differences found. */ 96 csinv endloop, diff, xzr, pl /* Last Dword or differences.*/ 97 bics has_nul, tmp1, tmp2 /* Non-zero if NUL terminator. */ 98 ccmp endloop, #0, #0, eq 99 b.eq .Lloop_aligned 100 101 /*Not reached the limit, must have found the end or a diff. */ 102 tbz limit_wd, #63, .Lnot_limit 103 104 /* Limit % 8 == 0 => all bytes significant. */ 105 ands limit, limit, #7 106 b.eq .Lnot_limit 107 108 lsl limit, limit, #3 /* Bits -> bytes. */ 109 mov mask, #~0 110CPU_BE( lsr mask, mask, limit ) 111CPU_LE( lsl mask, mask, limit ) 112 bic data1, data1, mask 113 bic data2, data2, mask 114 115 /* Make sure that the NUL byte is marked in the syndrome. */ 116 orr has_nul, has_nul, mask 117 118.Lnot_limit: 119 orr syndrome, diff, has_nul 120 b .Lcal_cmpresult 121 122.Lmutual_align: 123 /* 124 * Sources are mutually aligned, but are not currently at an 125 * alignment boundary. Round down the addresses and then mask off 126 * the bytes that precede the start point. 127 * We also need to adjust the limit calculations, but without 128 * overflowing if the limit is near ULONG_MAX. 129 */ 130 bic src1, src1, #7 131 bic src2, src2, #7 132 ldr data1, [src1], #8 133 neg tmp3, tmp1, lsl #3 /* 64 - bits(bytes beyond align). */ 134 ldr data2, [src2], #8 135 mov tmp2, #~0 136 sub limit_wd, limit, #1 /* limit != 0, so no underflow. */ 137 /* Big-endian. Early bytes are at MSB. */ 138CPU_BE( lsl tmp2, tmp2, tmp3 ) /* Shift (tmp1 & 63). */ 139 /* Little-endian. Early bytes are at LSB. */ 140CPU_LE( lsr tmp2, tmp2, tmp3 ) /* Shift (tmp1 & 63). */ 141 142 and tmp3, limit_wd, #7 143 lsr limit_wd, limit_wd, #3 144 /* Adjust the limit. Only low 3 bits used, so overflow irrelevant.*/ 145 add limit, limit, tmp1 146 add tmp3, tmp3, tmp1 147 orr data1, data1, tmp2 148 orr data2, data2, tmp2 149 add limit_wd, limit_wd, tmp3, lsr #3 150 b .Lstart_realigned 151 152/*when src1 offset is not equal to src2 offset...*/ 153.Lmisaligned8: 154 cmp limit, #8 155 b.lo .Ltiny8proc /*limit < 8... */ 156 /* 157 * Get the align offset length to compare per byte first. 158 * After this process, one string's address will be aligned.*/ 159 and tmp1, src1, #7 160 neg tmp1, tmp1 161 add tmp1, tmp1, #8 162 and tmp2, src2, #7 163 neg tmp2, tmp2 164 add tmp2, tmp2, #8 165 subs tmp3, tmp1, tmp2 166 csel pos, tmp1, tmp2, hi /*Choose the maximum. */ 167 /* 168 * Here, limit is not less than 8, so directly run .Ltinycmp 169 * without checking the limit.*/ 170 sub limit, limit, pos 171.Ltinycmp: 172 ldrb data1w, [src1], #1 173 ldrb data2w, [src2], #1 174 subs pos, pos, #1 175 ccmp data1w, #1, #0, ne /* NZCV = 0b0000. */ 176 ccmp data1w, data2w, #0, cs /* NZCV = 0b0000. */ 177 b.eq .Ltinycmp 178 cbnz pos, 1f /*find the null or unequal...*/ 179 cmp data1w, #1 180 ccmp data1w, data2w, #0, cs 181 b.eq .Lstart_align /*the last bytes are equal....*/ 1821: 183 sub result, data1, data2 184 ret 185 186.Lstart_align: 187 lsr limit_wd, limit, #3 188 cbz limit_wd, .Lremain8 189 /*process more leading bytes to make str1 aligned...*/ 190 ands xzr, src1, #7 191 b.eq .Lrecal_offset 192 add src1, src1, tmp3 /*tmp3 is positive in this branch.*/ 193 add src2, src2, tmp3 194 ldr data1, [src1], #8 195 ldr data2, [src2], #8 196 197 sub limit, limit, tmp3 198 lsr limit_wd, limit, #3 199 subs limit_wd, limit_wd, #1 200 201 sub tmp1, data1, zeroones 202 orr tmp2, data1, #REP8_7f 203 eor diff, data1, data2 /* Non-zero if differences found. */ 204 csinv endloop, diff, xzr, ne/*if limit_wd is 0,will finish the cmp*/ 205 bics has_nul, tmp1, tmp2 206 ccmp endloop, #0, #0, eq /*has_null is ZERO: no null byte*/ 207 b.ne .Lunequal_proc 208 /*How far is the current str2 from the alignment boundary...*/ 209 and tmp3, tmp3, #7 210.Lrecal_offset: 211 neg pos, tmp3 212.Lloopcmp_proc: 213 /* 214 * Divide the eight bytes into two parts. First,backwards the src2 215 * to an alignment boundary,load eight bytes from the SRC2 alignment 216 * boundary,then compare with the relative bytes from SRC1. 217 * If all 8 bytes are equal,then start the second part's comparison. 218 * Otherwise finish the comparison. 219 * This special handle can garantee all the accesses are in the 220 * thread/task space in avoid to overrange access. 221 */ 222 ldr data1, [src1,pos] 223 ldr data2, [src2,pos] 224 sub tmp1, data1, zeroones 225 orr tmp2, data1, #REP8_7f 226 bics has_nul, tmp1, tmp2 /* Non-zero if NUL terminator. */ 227 eor diff, data1, data2 /* Non-zero if differences found. */ 228 csinv endloop, diff, xzr, eq 229 cbnz endloop, .Lunequal_proc 230 231 /*The second part process*/ 232 ldr data1, [src1], #8 233 ldr data2, [src2], #8 234 subs limit_wd, limit_wd, #1 235 sub tmp1, data1, zeroones 236 orr tmp2, data1, #REP8_7f 237 eor diff, data1, data2 /* Non-zero if differences found. */ 238 csinv endloop, diff, xzr, ne/*if limit_wd is 0,will finish the cmp*/ 239 bics has_nul, tmp1, tmp2 240 ccmp endloop, #0, #0, eq /*has_null is ZERO: no null byte*/ 241 b.eq .Lloopcmp_proc 242 243.Lunequal_proc: 244 orr syndrome, diff, has_nul 245 cbz syndrome, .Lremain8 246.Lcal_cmpresult: 247 /* 248 * reversed the byte-order as big-endian,then CLZ can find the most 249 * significant zero bits. 250 */ 251CPU_LE( rev syndrome, syndrome ) 252CPU_LE( rev data1, data1 ) 253CPU_LE( rev data2, data2 ) 254 /* 255 * For big-endian we cannot use the trick with the syndrome value 256 * as carry-propagation can corrupt the upper bits if the trailing 257 * bytes in the string contain 0x01. 258 * However, if there is no NUL byte in the dword, we can generate 259 * the result directly. We can't just subtract the bytes as the 260 * MSB might be significant. 261 */ 262CPU_BE( cbnz has_nul, 1f ) 263CPU_BE( cmp data1, data2 ) 264CPU_BE( cset result, ne ) 265CPU_BE( cneg result, result, lo ) 266CPU_BE( ret ) 267CPU_BE( 1: ) 268 /* Re-compute the NUL-byte detection, using a byte-reversed value.*/ 269CPU_BE( rev tmp3, data1 ) 270CPU_BE( sub tmp1, tmp3, zeroones ) 271CPU_BE( orr tmp2, tmp3, #REP8_7f ) 272CPU_BE( bic has_nul, tmp1, tmp2 ) 273CPU_BE( rev has_nul, has_nul ) 274CPU_BE( orr syndrome, diff, has_nul ) 275 /* 276 * The MS-non-zero bit of the syndrome marks either the first bit 277 * that is different, or the top bit of the first zero byte. 278 * Shifting left now will bring the critical information into the 279 * top bits. 280 */ 281 clz pos, syndrome 282 lsl data1, data1, pos 283 lsl data2, data2, pos 284 /* 285 * But we need to zero-extend (char is unsigned) the value and then 286 * perform a signed 32-bit subtraction. 287 */ 288 lsr data1, data1, #56 289 sub result, data1, data2, lsr #56 290 ret 291 292.Lremain8: 293 /* Limit % 8 == 0 => all bytes significant. */ 294 ands limit, limit, #7 295 b.eq .Lret0 296.Ltiny8proc: 297 ldrb data1w, [src1], #1 298 ldrb data2w, [src2], #1 299 subs limit, limit, #1 300 301 ccmp data1w, #1, #0, ne /* NZCV = 0b0000. */ 302 ccmp data1w, data2w, #0, cs /* NZCV = 0b0000. */ 303 b.eq .Ltiny8proc 304 sub result, data1, data2 305 ret 306 307.Lret0: 308 mov result, #0 309 ret 310ENDPROC(strncmp) 311