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-rw-r--r--src/string/strstr.c166
1 files changed, 166 insertions, 0 deletions
diff --git a/src/string/strstr.c b/src/string/strstr.c
new file mode 100644
index 00000000..4d536a73
--- /dev/null
+++ b/src/string/strstr.c
@@ -0,0 +1,166 @@
+#include <string.h>
+#include <stdlib.h>
+#include <stdint.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;
+}
+
+#if 0
+static char *naive_strstr(const char *h, const char *n)
+{
+ size_t i;
+ for (i=0; n[i] && h[i]; i++)
+ for ( ; n[i] != h[i]; h++, i=0);
+ return n[i] ? 0 : (char *)h;
+}
+#endif
+
+#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)] = { 0 };
+ 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 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(h, n);
+ if (!h[2]) return 0;
+ if (!n[3]) return threebyte_strstr(h, n);
+ if (!h[3]) return 0;
+ if (!n[4]) return fourbyte_strstr(h, n);
+
+ return twoway_strstr(h, n);
+}