6
static char *twobyte_memmem(const unsigned char *h, size_t k, const unsigned char *n)
8
uint16_t nw = n[0]<<8 | n[1], hw = h[0]<<8 | h[1];
9
for (h++, k--; k; k--, hw = hw<<8 | *++h)
10
if (hw == nw) return (char *)h-1;
14
static char *threebyte_memmem(const unsigned char *h, size_t k, const unsigned char *n)
16
uint32_t nw = n[0]<<24 | n[1]<<16 | n[2]<<8;
17
uint32_t hw = h[0]<<24 | h[1]<<16 | h[2]<<8;
18
for (h+=2, k-=2; k; k--, hw = (hw|*++h)<<8)
19
if (hw == nw) return (char *)h-2;
23
static char *fourbyte_memmem(const unsigned char *h, size_t k, const unsigned char *n)
25
uint32_t nw = n[0]<<24 | n[1]<<16 | n[2]<<8 | n[3];
26
uint32_t hw = h[0]<<24 | h[1]<<16 | h[2]<<8 | h[3];
27
for (h+=3, k-=3; k; k--, hw = hw<<8 | *++h)
28
if (hw == nw) return (char *)h-3;
32
#define MAX(a,b) ((a)>(b)?(a):(b))
33
#define MIN(a,b) ((a)<(b)?(a):(b))
35
#define BITOP(a,b,op) \
36
((a)[(size_t)(b)/(8*sizeof *(a))] op (size_t)1<<((size_t)(b)%(8*sizeof *(a))))
38
static char *twoway_memmem(const unsigned char *h, const unsigned char *z, const unsigned char *n, size_t l)
40
size_t i, ip, jp, k, p, ms, p0, mem, mem0;
41
size_t byteset[32 / sizeof(size_t)] = { 0 };
44
/* Computing length of needle and fill shift table */
46
BITOP(byteset, n[i], |=), shift[n[i]] = i+1;
48
/* Compute maximal suffix */
49
ip = -1; jp = 0; k = p = 1;
51
if (n[ip+k] == n[jp+k]) {
56
} else if (n[ip+k] > n[jp+k]) {
68
/* And with the opposite comparison */
69
ip = -1; jp = 0; k = p = 1;
71
if (n[ip+k] == n[jp+k]) {
76
} else if (n[ip+k] < n[jp+k]) {
85
if (ip+1 > ms+1) ms = ip;
88
/* Periodic needle? */
89
if (memcmp(n, n+p, ms+1)) {
91
p = MAX(ms, l-ms-1) + 1;
97
/* If remainder of haystack is shorter than needle, done */
98
if (z-h < l) return 0;
100
/* Check last byte first; advance by shift on mismatch */
101
if (BITOP(byteset, h[l-1], &)) {
104
if (mem0 && mem && k < p) k = l-p;
115
/* Compare right half */
116
for (k=MAX(ms+1,mem); n[k] && n[k] == h[k]; k++);
122
/* Compare left half */
123
for (k=ms+1; k>mem && n[k-1] == h[k-1]; k--);
124
if (k == mem) return (char *)h;
130
void *memmem(const void *h0, size_t k, const void *n0, size_t l)
132
const unsigned char *h = h0, *n = n0;
134
/* Return immediately on empty needle */
135
if (!l) return (void *)h;
137
/* Return immediately when needle is longer than haystack */
140
/* Use faster algorithms for short needles */
141
h = memchr(h0, *n, k);
142
if (!h || l==1) return (void *)h;
143
if (l==2) return twobyte_memmem(h, k, n);
144
if (l==3) return threebyte_memmem(h, k, n);
145
if (l==4) return fourbyte_memmem(h, k, n);
147
return twoway_memmem(h, h+k, n, l);