| #define _GNU_SOURCE |
| #include <stdint.h> |
| #include <string.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 += 2, k -= 2; k; k--, hw = hw << 8 | *h++) |
| if (hw == nw) |
| return (char*)h - 2; |
| return hw == nw ? (char*)h - 2 : 0; |
| } |
| |
| static char* threebyte_memmem(const unsigned char* h, size_t k, const unsigned char* n) { |
| uint32_t nw = ((uint32_t)n[0]) << 24 | n[1] << 16 | n[2] << 8; |
| uint32_t hw = ((uint32_t)h[0]) << 24 | h[1] << 16 | h[2] << 8; |
| for (h += 3, k -= 3; k; k--, hw = (hw | *h++) << 8) |
| if (hw == nw) |
| return (char*)h - 3; |
| return hw == nw ? (char*)h - 3 : 0; |
| } |
| |
| static char* fourbyte_memmem(const unsigned char* h, size_t k, const unsigned char* n) { |
| uint32_t nw = ((uint32_t)n[0]) << 24 | n[1] << 16 | n[2] << 8 | n[3]; |
| uint32_t hw = ((uint32_t)h[0]) << 24 | h[1] << 16 | h[2] << 8 | h[3]; |
| for (h += 4, k -= 4; k; k--, hw = hw << 8 | *h++) |
| if (hw == nw) |
| return (char*)h - 4; |
| return hw == nw ? (char*)h - 4 : 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)] = {}; |
| 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); |
| } |