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Diffstat (limited to 'lib/libc/string/memmem.c')
| -rw-r--r-- | lib/libc/string/memmem.c | 211 |
1 files changed, 211 insertions, 0 deletions
diff --git a/lib/libc/string/memmem.c b/lib/libc/string/memmem.c new file mode 100644 index 000000000000..4a244b5964ce --- /dev/null +++ b/lib/libc/string/memmem.c @@ -0,0 +1,211 @@ +/*- + * SPDX-License-Identifier: MIT + * + * Copyright (c) 2005-2014 Rich Felker, et al. + * + * Permission is hereby granted, free of charge, to any person obtaining + * a copy of this software and associated documentation files (the + * "Software"), to deal in the Software without restriction, including + * without limitation the rights to use, copy, modify, merge, publish, + * distribute, sublicense, and/or sell copies of the Software, and to + * permit persons to whom the Software is furnished to do so, subject to + * the following conditions: + * + * The above copyright notice and this permission notice shall be + * included in all copies or substantial portions of the Software. + * + * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, + * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF + * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. + * IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY + * CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, + * TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE + * SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE. + */ +#include <stdint.h> +#include <string.h> + +static char * +twobyte_memmem(const unsigned char *h, size_t k, const unsigned char *n) +{ + uint16_t nw = n[0] << 8 | n[1], hw = h[0] << 8 | h[1]; + for (h += 2, k -= 2; k; k--, hw = hw << 8 | *h++) + if (hw == nw) + return (char *)h - 2; + return hw == nw ? (char *)h - 2 : 0; +} + +static char * +threebyte_memmem(const unsigned char *h, size_t k, const unsigned char *n) +{ + uint32_t nw = (uint32_t)n[0] << 24 | n[1] << 16 | n[2] << 8; + uint32_t hw = (uint32_t)h[0] << 24 | h[1] << 16 | h[2] << 8; + for (h += 3, k -= 3; k; k--, hw = (hw | *h++) << 8) + if (hw == nw) + return (char *)h - 3; + return hw == nw ? (char *)h - 3 : 0; +} + +static char * +fourbyte_memmem(const unsigned char *h, size_t k, const unsigned char *n) +{ + uint32_t nw = (uint32_t)n[0] << 24 | n[1] << 16 | n[2] << 8 | n[3]; + uint32_t hw = (uint32_t)h[0] << 24 | h[1] << 16 | h[2] << 8 | h[3]; + for (h += 4, k -= 4; k; k--, hw = hw << 8 | *h++) + if (hw == nw) + return (char *)h - 4; + return hw == nw ? (char *)h - 4 : 0; +} + +#define MAX(a, b) ((a) > (b) ? (a) : (b)) +#define MIN(a, b) ((a) < (b) ? (a) : (b)) + +#define BITOP(a, b, op) \ + ((a)[(size_t)(b) / (8 * sizeof *(a))] op \ + (size_t)1 << ((size_t)(b) % (8 * sizeof *(a)))) + +/* + * Two Way string search algorithm, with a bad shift table applied to the last + * byte of the window. A bit array marks which entries in the shift table are + * initialized to avoid fully initializing a 1kb/2kb table. + * + * Reference: CROCHEMORE M., PERRIN D., 1991, Two-way string-matching, + * Journal of the ACM 38(3):651-675 + */ +static char * +twoway_memmem(const unsigned char *h, const unsigned char *z, + const unsigned char *n, size_t l) +{ + size_t i, ip, jp, k, p, ms, p0, mem, mem0; + size_t byteset[32 / sizeof(size_t)] = { 0 }; + size_t shift[256]; + + /* Computing length of needle and fill shift table */ + for (i = 0; i < l; i++) + BITOP(byteset, n[i], |=), shift[n[i]] = i + 1; + + /* Compute maximal suffix */ + ip = -1; + jp = 0; + k = p = 1; + while (jp + k < l) { + if (n[ip + k] == n[jp + k]) { + if (k == p) { + jp += p; + k = 1; + } else + k++; + } else if (n[ip + k] > n[jp + k]) { + jp += k; + k = 1; + p = jp - ip; + } else { + ip = jp++; + k = p = 1; + } + } + ms = ip; + p0 = p; + + /* And with the opposite comparison */ + ip = -1; + jp = 0; + k = p = 1; + while (jp + k < l) { + if (n[ip + k] == n[jp + k]) { + if (k == p) { + jp += p; + k = 1; + } else + k++; + } else if (n[ip + k] < n[jp + k]) { + jp += k; + k = 1; + p = jp - ip; + } else { + ip = jp++; + k = p = 1; + } + } + if (ip + 1 > ms + 1) + ms = ip; + else + p = p0; + + /* Periodic needle? */ + if (memcmp(n, n + p, ms + 1)) { + mem0 = 0; + p = MAX(ms, l - ms - 1) + 1; + } else + mem0 = l - p; + mem = 0; + + /* Search loop */ + for (;;) { + /* If remainder of haystack is shorter than needle, done */ + if (z - h < l) + return 0; + + /* Check last byte first; advance by shift on mismatch */ + if (BITOP(byteset, h[l - 1], &)) { + k = l - shift[h[l - 1]]; + if (k) { + if (k < mem) + k = mem; + h += k; + mem = 0; + continue; + } + } else { + h += l; + mem = 0; + continue; + } + + /* Compare right half */ + for (k = MAX(ms + 1, mem); k < l && n[k] == h[k]; k++) + ; + if (k < l) { + h += k - ms; + mem = 0; + continue; + } + /* Compare left half */ + for (k = ms + 1; k > mem && n[k - 1] == h[k - 1]; k--) + ; + if (k <= mem) + return (char *)h; + h += p; + mem = mem0; + } +} + +void * +memmem(const void *h0, size_t k, const void *n0, size_t l) +{ + const unsigned char *h = h0, *n = n0; + + /* Return immediately on empty needle */ + if (!l) + return (void *)h; + + /* Return immediately when needle is longer than haystack */ + if (k < l) + return 0; + + /* Use faster algorithms for short needles */ + h = memchr(h0, *n, k); + if (!h || l == 1) + return (void *)h; + k -= h - (const unsigned char *)h0; + if (k < l) + return 0; + if (l == 2) + return twobyte_memmem(h, k, n); + if (l == 3) + return threebyte_memmem(h, k, n); + if (l == 4) + return fourbyte_memmem(h, k, n); + + return twoway_memmem(h, h + k, n, l); +} |