| #include <stdint.h> |
| #include <string.h> |
| |
| static char* twobyte_strstr(const unsigned char* h, const unsigned char* n) { |
| uint16_t nw = n[0] << 8 | n[1], hw = h[0] << 8 | h[1]; |
| for (h++; *h && hw != nw; hw = hw << 8 | *++h) |
| ; |
| return *h ? (char*)h - 1 : 0; |
| } |
| |
| static char* threebyte_strstr(const unsigned char* h, 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; *h && hw != nw; hw = (hw | *++h) << 8) |
| ; |
| return *h ? (char*)h - 2 : 0; |
| } |
| |
| static char* fourbyte_strstr(const unsigned char* h, 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; *h && hw != nw; hw = hw << 8 | *++h) |
| ; |
| return *h ? (char*)h - 3 : 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_strstr(const unsigned char* h, const unsigned char* n) { |
| const unsigned char* z; |
| size_t l, 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 (l = 0; n[l] && h[l]; l++) |
| BITOP(byteset, n[l], |=) |
| , shift[n[l]] = l + 1; |
| if (n[l]) |
| return 0; /* hit the end of h */ |
| |
| /* 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; |
| |
| /* Initialize incremental end-of-haystack pointer */ |
| z = h; |
| |
| /* Search loop */ |
| for (;;) { |
| /* Update incremental end-of-haystack pointer */ |
| if (z - h < l) { |
| /* Fast estimate for MIN(l,63) */ |
| size_t grow = l | 63; |
| const unsigned char* z2 = memchr(z, 0, grow); |
| if (z2) { |
| z = z2; |
| if (z - h < l) |
| return 0; |
| } else |
| z += grow; |
| } |
| |
| /* Check last byte first; advance by shift on mismatch */ |
| if (BITOP(byteset, h[l - 1], &)) { |
| k = l - shift[h[l - 1]]; |
| // printf("adv by %zu (on %c) at [%s] (%zu;l=%zu)\n", k, h[l-1], h, shift[h[l-1]], l); |
| 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); n[k] && n[k] == h[k]; k++) |
| ; |
| if (n[k]) { |
| 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; |
| } |
| } |
| |
| char* strstr(const char* h, const char* n) { |
| /* Return immediately on empty needle */ |
| if (!n[0]) |
| return (char*)h; |
| |
| /* Use faster algorithms for short needles */ |
| h = strchr(h, *n); |
| if (!h || !n[1]) |
| return (char*)h; |
| if (!h[1]) |
| return 0; |
| if (!n[2]) |
| return twobyte_strstr((void*)h, (void*)n); |
| if (!h[2]) |
| return 0; |
| if (!n[3]) |
| return threebyte_strstr((void*)h, (void*)n); |
| if (!h[3]) |
| return 0; |
| if (!n[4]) |
| return fourbyte_strstr((void*)h, (void*)n); |
| |
| return twoway_strstr((void*)h, (void*)n); |
| } |