1#define _GNU_SOURCE
2#include <string.h>
3#include <stdint.h>
4
5static char *twobyte_memmem(const unsigned char *h, size_t k, const unsigned char *n)
6{
7	uint16_t nw = n[0]<<8 | n[1], hw = h[0]<<8 | h[1];
8	for (h++, k--; k; k--, hw = hw<<8 | *++h)
9		if (hw == nw) return (char *)h-1;
10	return 0;
11}
12
13static char *threebyte_memmem(const unsigned char *h, size_t k, const unsigned char *n)
14{
15	uint32_t nw = n[0]<<24 | n[1]<<16 | n[2]<<8;
16	uint32_t hw = h[0]<<24 | h[1]<<16 | h[2]<<8;
17	for (h+=2, k-=2; k; k--, hw = (hw|*++h)<<8)
18		if (hw == nw) return (char *)h-2;
19	return 0;
20}
21
22static char *fourbyte_memmem(const unsigned char *h, size_t k, const unsigned char *n)
23{
24	uint32_t nw = n[0]<<24 | n[1]<<16 | n[2]<<8 | n[3];
25	uint32_t hw = h[0]<<24 | h[1]<<16 | h[2]<<8 | h[3];
26	for (h+=3, k-=3; k; k--, hw = hw<<8 | *++h)
27		if (hw == nw) return (char *)h-3;
28	return 0;
29}
30
31#define MAX(a,b) ((a)>(b)?(a):(b))
32#define MIN(a,b) ((a)<(b)?(a):(b))
33
34#define BITOP(a,b,op) \
35 ((a)[(size_t)(b)/(8*sizeof *(a))] op (size_t)1<<((size_t)(b)%(8*sizeof *(a))))
36
37static char *twoway_memmem(const unsigned char *h, const unsigned char *z, const unsigned char *n, size_t l)
38{
39	size_t i, ip, jp, k, p, ms, p0, mem, mem0;
40	size_t byteset[32 / sizeof(size_t)] = { 0 };
41	size_t shift[256];
42
43	/* Computing length of needle and fill shift table */
44	for (i=0; i<l; i++)
45		BITOP(byteset, n[i], |=), shift[n[i]] = i+1;
46
47	/* Compute maximal suffix */
48	ip = -1; jp = 0; k = p = 1;
49	while (jp+k<l) {
50		if (n[ip+k] == n[jp+k]) {
51			if (k == p) {
52				jp += p;
53				k = 1;
54			} else k++;
55		} else if (n[ip+k] > n[jp+k]) {
56			jp += k;
57			k = 1;
58			p = jp - ip;
59		} else {
60			ip = jp++;
61			k = p = 1;
62		}
63	}
64	ms = ip;
65	p0 = p;
66
67	/* And with the opposite comparison */
68	ip = -1; jp = 0; k = p = 1;
69	while (jp+k<l) {
70		if (n[ip+k] == n[jp+k]) {
71			if (k == p) {
72				jp += p;
73				k = 1;
74			} else k++;
75		} else if (n[ip+k] < n[jp+k]) {
76			jp += k;
77			k = 1;
78			p = jp - ip;
79		} else {
80			ip = jp++;
81			k = p = 1;
82		}
83	}
84	if (ip+1 > ms+1) ms = ip;
85	else p = p0;
86
87	/* Periodic needle? */
88	if (memcmp(n, n+p, ms+1)) {
89		mem0 = 0;
90		p = MAX(ms, l-ms-1) + 1;
91	} else mem0 = l-p;
92	mem = 0;
93
94	/* Search loop */
95	for (;;) {
96		/* If remainder of haystack is shorter than needle, done */
97		if (z-h < l) return 0;
98
99		/* Check last byte first; advance by shift on mismatch */
100		if (BITOP(byteset, h[l-1], &)) {
101			k = l-shift[h[l-1]];
102			if (k) {
103				if (mem0 && mem && k < p) k = l-p;
104				h += k;
105				mem = 0;
106				continue;
107			}
108		} else {
109			h += l;
110			mem = 0;
111			continue;
112		}
113
114		/* Compare right half */
115		for (k=MAX(ms+1,mem); k<l && n[k] == h[k]; k++);
116		if (k < l) {
117			h += k-ms;
118			mem = 0;
119			continue;
120		}
121		/* Compare left half */
122		for (k=ms+1; k>mem && n[k-1] == h[k-1]; k--);
123		if (k <= mem) return (char *)h;
124		h += p;
125		mem = mem0;
126	}
127}
128
129void *memmem(const void *h0, size_t k, const void *n0, size_t l)
130{
131	const unsigned char *h = h0, *n = n0;
132
133	/* Return immediately on empty needle */
134	if (!l) return (void *)h;
135
136	/* Return immediately when needle is longer than haystack */
137	if (k<l) return 0;
138
139	/* Use faster algorithms for short needles */
140	h = memchr(h0, *n, k);
141	if (!h || l==1) return (void *)h;
142	k -= h - (const unsigned char *)h0;
143	if (k<l) return 0;
144	if (l==2) return twobyte_memmem(h, k, n);
145	if (l==3) return threebyte_memmem(h, k, n);
146	if (l==4) return fourbyte_memmem(h, k, n);
147
148	return twoway_memmem(h, h+k, n, l);
149}
150