1 #define _GNU_SOURCE
2 #include <string.h>
3 #include <stdint.h>
4
twobyte_memmem(const unsigned char * h,size_t k,const unsigned char * n)5 static 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+=2, k-=2; k; k--, hw = hw<<8 | *h++)
9 if (hw == nw) return (char *)h-2;
10 return hw == nw ? (char *)h-2 : 0;
11 }
12
threebyte_memmem(const unsigned char * h,size_t k,const unsigned char * n)13 static 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+=3, k-=3; k; k--, hw = (hw|*h++)<<8)
18 if (hw == nw) return (char *)h-3;
19 return hw == nw ? (char *)h-3 : 0;
20 }
21
fourbyte_memmem(const unsigned char * h,size_t k,const unsigned char * n)22 static 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+=4, k-=4; k; k--, hw = hw<<8 | *h++)
27 if (hw == nw) return (char *)h-4;
28 return hw == nw ? (char *)h-4 : 0;
29 }
30
31 #ifndef MAX
32 #define MAX(a,b) ((a)>(b)?(a):(b))
33 #endif
34 #ifndef MIN
35 #define MIN(a,b) ((a)<(b)?(a):(b))
36 #endif
37
38 #define BITOP(a,b,op) \
39 ((a)[(size_t)(b)/(8*sizeof *(a))] op (size_t)1<<((size_t)(b)%(8*sizeof *(a))))
40
twoway_memmem(const unsigned char * h,const unsigned char * z,const unsigned char * n,size_t l)41 static char *twoway_memmem(const unsigned char *h, const unsigned char *z, const unsigned char *n, size_t l)
42 {
43 size_t i, ip, jp, k, p, ms, p0, mem, mem0;
44 size_t byteset[32 / sizeof(size_t)] = { 0 };
45 size_t shift[256];
46
47 /* Computing length of needle and fill shift table */
48 for (i=0; i<l; i++)
49 BITOP(byteset, n[i], |=), shift[n[i]] = i+1;
50
51 /* Compute maximal suffix */
52 ip = -1; jp = 0; k = p = 1;
53 while (jp+k<l) {
54 if (n[ip+k] == n[jp+k]) {
55 if (k == p) {
56 jp += p;
57 k = 1;
58 } else k++;
59 } else if (n[ip+k] > n[jp+k]) {
60 jp += k;
61 k = 1;
62 p = jp - ip;
63 } else {
64 ip = jp++;
65 k = p = 1;
66 }
67 }
68 ms = ip;
69 p0 = p;
70
71 /* And with the opposite comparison */
72 ip = -1; jp = 0; k = p = 1;
73 while (jp+k<l) {
74 if (n[ip+k] == n[jp+k]) {
75 if (k == p) {
76 jp += p;
77 k = 1;
78 } else k++;
79 } else if (n[ip+k] < n[jp+k]) {
80 jp += k;
81 k = 1;
82 p = jp - ip;
83 } else {
84 ip = jp++;
85 k = p = 1;
86 }
87 }
88 if (ip+1 > ms+1) ms = ip;
89 else p = p0;
90
91 /* Periodic needle? */
92 if (memcmp(n, n+p, ms+1)) {
93 mem0 = 0;
94 p = MAX(ms, l-ms-1) + 1;
95 } else mem0 = l-p;
96 mem = 0;
97
98 /* Search loop */
99 for (;;) {
100 /* If remainder of haystack is shorter than needle, done */
101 if (z-h < l) return 0;
102
103 /* Check last byte first; advance by shift on mismatch */
104 if (BITOP(byteset, h[l-1], &)) {
105 k = l-shift[h[l-1]];
106 if (k) {
107 if (k < mem) k = mem;
108 h += k;
109 mem = 0;
110 continue;
111 }
112 } else {
113 h += l;
114 mem = 0;
115 continue;
116 }
117
118 /* Compare right half */
119 for (k=MAX(ms+1,mem); k<l && n[k] == h[k]; k++);
120 if (k < l) {
121 h += k-ms;
122 mem = 0;
123 continue;
124 }
125 /* Compare left half */
126 for (k=ms+1; k>mem && n[k-1] == h[k-1]; k--);
127 if (k <= mem) return (char *)h;
128 h += p;
129 mem = mem0;
130 }
131 }
132
memmem(const void * h0,size_t k,const void * n0,size_t l)133 void *memmem(const void *h0, size_t k, const void *n0, size_t l)
134 {
135 const unsigned char *h = h0, *n = n0;
136
137 /* Return immediately on empty needle */
138 if (!l) return (void *)h;
139
140 /* Return immediately when needle is longer than haystack */
141 if (k<l) return 0;
142
143 /* Use faster algorithms for short needles */
144 h = memchr(h0, *n, k);
145 if (!h || l==1) return (void *)h;
146 k -= h - (const unsigned char *)h0;
147 if (k<l) return 0;
148 if (l==2) return twobyte_memmem(h, k, n);
149 if (l==3) return threebyte_memmem(h, k, n);
150 if (l==4) return fourbyte_memmem(h, k, n);
151
152 return twoway_memmem(h, h+k, n, l);
153 }
154