1130812Smarcel#define _GNU_SOURCE 2130812Smarcel#include <stdint.h> 3130812Smarcel#include <string.h> 4130812Smarcel 5130812Smarcelstatic char* twobyte_memmem(const unsigned char* h, size_t k, const unsigned char* n) { 6130812Smarcel uint16_t nw = n[0] << 8 | n[1], hw = h[0] << 8 | h[1]; 7130812Smarcel for (h += 2, k -= 2; k; k--, hw = hw << 8 | *h++) 8130812Smarcel if (hw == nw) 9130812Smarcel return (char*)h - 2; 10130812Smarcel return hw == nw ? (char*)h - 2 : 0; 11130812Smarcel} 12130812Smarcel 13130812Smarcelstatic char* threebyte_memmem(const unsigned char* h, size_t k, const unsigned char* n) { 14130812Smarcel uint32_t nw = n[0] << 24 | n[1] << 16 | n[2] << 8; 15130812Smarcel uint32_t hw = h[0] << 24 | h[1] << 16 | h[2] << 8; 16130812Smarcel for (h += 3, k -= 3; k; k--, hw = (hw | *h++) << 8) 17130812Smarcel if (hw == nw) 18130812Smarcel return (char*)h - 3; 19130812Smarcel return hw == nw ? (char*)h - 3 : 0; 20130812Smarcel} 21130812Smarcel 22130812Smarcelstatic char* fourbyte_memmem(const unsigned char* h, size_t k, const unsigned char* n) { 23130812Smarcel uint32_t nw = n[0] << 24 | n[1] << 16 | n[2] << 8 | n[3]; 24130812Smarcel uint32_t hw = h[0] << 24 | h[1] << 16 | h[2] << 8 | h[3]; 25130812Smarcel for (h += 4, k -= 4; k; k--, hw = hw << 8 | *h++) 26130812Smarcel if (hw == nw) 27130812Smarcel return (char*)h - 4; 28130812Smarcel return hw == nw ? (char*)h - 4 : 0; 29130812Smarcel} 30130812Smarcel 31130812Smarcel#define MAX(a, b) ((a) > (b) ? (a) : (b)) 32130812Smarcel#define MIN(a, b) ((a) < (b) ? (a) : (b)) 33130812Smarcel 34130812Smarcel#define BITOP(a, b, op) \ 35130812Smarcel ((a)[(size_t)(b) / (8 * sizeof *(a))] op(size_t) 1 << ((size_t)(b) % (8 * sizeof *(a)))) 36130812Smarcel 37130812Smarcelstatic char* twoway_memmem(const unsigned char* h, const unsigned char* z, const unsigned char* n, 38130812Smarcel size_t l) { 39130812Smarcel size_t i, ip, jp, k, p, ms, p0, mem, mem0; 40130812Smarcel size_t byteset[32 / sizeof(size_t)] = {}; 41130812Smarcel size_t shift[256]; 42130812Smarcel 43130812Smarcel /* Computing length of needle and fill shift table */ 44130812Smarcel for (i = 0; i < l; i++) 45130812Smarcel BITOP(byteset, n[i], |=) 46130812Smarcel , shift[n[i]] = i + 1; 47130812Smarcel 48130812Smarcel /* Compute maximal suffix */ 49130812Smarcel ip = -1; 50130812Smarcel jp = 0; 51130812Smarcel k = p = 1; 52130812Smarcel while (jp + k < l) { 53130812Smarcel if (n[ip + k] == n[jp + k]) { 54130812Smarcel if (k == p) { 55130812Smarcel jp += p; 56130812Smarcel k = 1; 57130812Smarcel } else 58130812Smarcel k++; 59130812Smarcel } else if (n[ip + k] > n[jp + k]) { 60130812Smarcel jp += k; 61130812Smarcel k = 1; 62130812Smarcel p = jp - ip; 63130812Smarcel } else { 64130812Smarcel ip = jp++; 65130812Smarcel k = p = 1; 66130812Smarcel } 67130812Smarcel } 68130812Smarcel ms = ip; 69130812Smarcel p0 = p; 70130812Smarcel 71130812Smarcel /* And with the opposite comparison */ 72130812Smarcel ip = -1; 73130812Smarcel jp = 0; 74130812Smarcel k = p = 1; 75130812Smarcel while (jp + k < l) { 76130812Smarcel if (n[ip + k] == n[jp + k]) { 77130812Smarcel if (k == p) { 78130812Smarcel jp += p; 79130812Smarcel k = 1; 80130812Smarcel } else 81130812Smarcel k++; 82130812Smarcel } else if (n[ip + k] < n[jp + k]) { 83130812Smarcel jp += k; 84130812Smarcel k = 1; 85130812Smarcel p = jp - ip; 86130812Smarcel } else { 87130812Smarcel ip = jp++; 88130812Smarcel k = p = 1; 89130812Smarcel } 90130812Smarcel } 91130812Smarcel if (ip + 1 > ms + 1) 92130812Smarcel ms = ip; 93130812Smarcel else 94130812Smarcel p = p0; 95130812Smarcel 96130812Smarcel /* Periodic needle? */ 97130812Smarcel if (memcmp(n, n + p, ms + 1)) { 98130812Smarcel mem0 = 0; 99130812Smarcel p = MAX(ms, l - ms - 1) + 1; 100130812Smarcel } else 101130812Smarcel mem0 = l - p; 102130812Smarcel mem = 0; 103130812Smarcel 104130812Smarcel /* Search loop */ 105130812Smarcel for (;;) { 106130812Smarcel /* If remainder of haystack is shorter than needle, done */ 107130812Smarcel if (z - h < l) 108130812Smarcel return 0; 109130812Smarcel 110130812Smarcel /* Check last byte first; advance by shift on mismatch */ 111130812Smarcel if (BITOP(byteset, h[l - 1], &)) { 112130812Smarcel k = l - shift[h[l - 1]]; 113130812Smarcel if (k) { 114130812Smarcel if (mem0 && mem && k < p) 115130812Smarcel k = l - p; 116130812Smarcel h += k; 117130812Smarcel mem = 0; 118130812Smarcel continue; 119130812Smarcel } 120130812Smarcel } else { 121130812Smarcel h += l; 122130812Smarcel mem = 0; 123130812Smarcel continue; 124130812Smarcel } 125130812Smarcel 126130812Smarcel /* Compare right half */ 127130812Smarcel for (k = MAX(ms + 1, mem); k < l && n[k] == h[k]; k++) 128130812Smarcel ; 129130812Smarcel if (k < l) { 130130812Smarcel h += k - ms; 131130812Smarcel mem = 0; 132130812Smarcel continue; 133130812Smarcel } 134130812Smarcel /* Compare left half */ 135130812Smarcel for (k = ms + 1; k > mem && n[k - 1] == h[k - 1]; k--) 136130812Smarcel ; 137130812Smarcel if (k <= mem) 138130812Smarcel return (char*)h; 139130812Smarcel h += p; 140130812Smarcel mem = mem0; 141130812Smarcel } 142130812Smarcel} 143130812Smarcel 144130812Smarcelvoid* memmem(const void* h0, size_t k, const void* n0, size_t l) { 145130812Smarcel const unsigned char *h = h0, *n = n0; 146130812Smarcel 147130812Smarcel /* Return immediately on empty needle */ 148130812Smarcel if (!l) 149130812Smarcel return (void*)h; 150130812Smarcel 151130812Smarcel /* Return immediately when needle is longer than haystack */ 152130812Smarcel if (k < l) 153130812Smarcel return 0; 154130812Smarcel 155130812Smarcel /* Use faster algorithms for short needles */ 156130812Smarcel h = memchr(h0, *n, k); 157130812Smarcel if (!h || l == 1) 158130812Smarcel return (void*)h; 159130812Smarcel k -= h - (const unsigned char*)h0; 160130812Smarcel if (k < l) 161130812Smarcel return 0; 162130812Smarcel if (l == 2) 163130812Smarcel return twobyte_memmem(h, k, n); 164130812Smarcel if (l == 3) 165130812Smarcel return threebyte_memmem(h, k, n); 166130812Smarcel if (l == 4) 167130812Smarcel return fourbyte_memmem(h, k, n); 168130812Smarcel 169130812Smarcel return twoway_memmem(h, h + k, n, l); 170130812Smarcel} 171130812Smarcel