1 /* $OpenBSD: memmem.c,v 1.5 2020/04/16 12:39:28 claudio Exp $ */
4 * Copyright (c) 2005-2020 Rich Felker, et al.
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11 * permit persons to whom the Software is furnished to do so, subject to
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14 * The above copyright notice and this permission notice shall be
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17 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
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19 * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
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30 twobyte_memmem(const unsigned char *h, size_t k, const unsigned char *n)
32 uint16_t nw = n[0]<<8 | n[1], hw = h[0]<<8 | h[1];
33 for (h+=2, k-=2; k; k--, hw = hw<<8 | *h++)
34 if (hw == nw) return (char *)h-2;
35 return hw == nw ? (char *)h-2 : 0;
39 threebyte_memmem(const unsigned char *h, size_t k, const unsigned char *n)
41 uint32_t nw = n[0]<<24 | n[1]<<16 | n[2]<<8;
42 uint32_t hw = h[0]<<24 | h[1]<<16 | h[2]<<8;
43 for (h+=3, k-=3; k; k--, hw = (hw|*h++)<<8)
44 if (hw == nw) return (char *)h-3;
45 return hw == nw ? (char *)h-3 : 0;
49 fourbyte_memmem(const unsigned char *h, size_t k, const unsigned char *n)
51 uint32_t nw = n[0]<<24 | n[1]<<16 | n[2]<<8 | n[3];
52 uint32_t hw = h[0]<<24 | h[1]<<16 | h[2]<<8 | h[3];
53 for (h+=4, k-=4; k; k--, hw = hw<<8 | *h++)
54 if (hw == nw) return (char *)h-4;
55 return hw == nw ? (char *)h-4 : 0;
58 #define MAX(a,b) ((a)>(b)?(a):(b))
59 #define MIN(a,b) ((a)<(b)?(a):(b))
61 #define BITOP(a,b,op) \
62 ((a)[(size_t)(b)/(8*sizeof *(a))] op (size_t)1<<((size_t)(b)%(8*sizeof *(a))))
65 * Maxime Crochemore and Dominique Perrin, Two-way string-matching,
66 * Journal of the ACM, 38(3):651-675, July 1991.
69 twoway_memmem(const unsigned char *h, const unsigned char *z,
70 const unsigned char *n, size_t l)
72 size_t i, ip, jp, k, p, ms, p0, mem, mem0;
73 size_t byteset[32 / sizeof(size_t)] = { 0 };
76 /* Computing length of needle and fill shift table */
78 BITOP(byteset, n[i], |=), shift[n[i]] = i+1;
80 /* Compute maximal suffix */
81 ip = -1; jp = 0; k = p = 1;
83 if (n[ip+k] == n[jp+k]) {
88 } else if (n[ip+k] > n[jp+k]) {
100 /* And with the opposite comparison */
101 ip = -1; jp = 0; k = p = 1;
103 if (n[ip+k] == n[jp+k]) {
108 } else if (n[ip+k] < n[jp+k]) {
117 if (ip+1 > ms+1) ms = ip;
120 /* Periodic needle? */
121 if (memcmp(n, n+p, ms+1)) {
123 p = MAX(ms, l-ms-1) + 1;
129 /* If remainder of haystack is shorter than needle, done */
130 if (z-h < l) return 0;
132 /* Check last byte first; advance by shift on mismatch */
133 if (BITOP(byteset, h[l-1], &)) {
136 if (k < mem) k = mem;
147 /* Compare right half */
148 for (k=MAX(ms+1,mem); k<l && n[k] == h[k]; k++);
154 /* Compare left half */
155 for (k=ms+1; k>mem && n[k-1] == h[k-1]; k--);
156 if (k <= mem) return (char *)h;
163 memmem(const void *h0, size_t k, const void *n0, size_t l)
165 const unsigned char *h = h0, *n = n0;
167 /* Return immediately on empty needle */
168 if (!l) return (void *)h;
170 /* Return immediately when needle is longer than haystack */
173 /* Use faster algorithms for short needles */
174 h = memchr(h0, *n, k);
175 if (!h || l==1) return (void *)h;
176 k -= h - (const unsigned char *)h0;
178 if (l==2) return twobyte_memmem(h, k, n);
179 if (l==3) return threebyte_memmem(h, k, n);
180 if (l==4) return fourbyte_memmem(h, k, n);
182 return twoway_memmem(h, h+k, n, l);