| #define _GNU_SOURCE |
| #include <string.h> |
| #include <stdint.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++, k--; k; k--, hw = hw<<8 | *++h) |
| if (hw == nw) return (char *)h-1; |
| return 0; |
| } |
| |
| static char *threebyte_memmem(const unsigned char *h, size_t k, const unsigned char *n) |
| { |
| uint32_t nw = n[0]<<24 | n[1]<<16 | n[2]<<8; |
| uint32_t hw = h[0]<<24 | h[1]<<16 | h[2]<<8; |
| for (h+=2, k-=2; k; k--, hw = (hw|*++h)<<8) |
| if (hw == nw) return (char *)h-2; |
| return 0; |
| } |
| |
| static char *fourbyte_memmem(const unsigned char *h, size_t k, const unsigned char *n) |
| { |
| uint32_t nw = n[0]<<24 | n[1]<<16 | n[2]<<8 | n[3]; |
| uint32_t hw = h[0]<<24 | h[1]<<16 | h[2]<<8 | h[3]; |
| for (h+=3, k-=3; k; k--, hw = hw<<8 | *++h) |
| if (hw == nw) return (char *)h-3; |
| return 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)))) |
| |
| 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 (mem0 && mem && k < p) k = l-p; |
| 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); |
| } |