initial check-in, version 0.5.0

src/string/wcsstr.c

@@ -0,0 +1,117 @@
+#include <wchar.h>
+#include <string.h>
+#include <stdlib.h>
+#include <stdint.h>
+
+static wchar_t *naive_wcsstr(const wchar_t *h, const wchar_t *n)
+{
+	size_t i;
+	for (i=0; n[i] && h[i]; i++)
+	for (   ; n[i] != h[i]; h++, i=0);
+	return n[i] ? 0 : (wchar_t *)h;
+}
+
+#define MAX(a,b) ((a)>(b)?(a):(b))
+#define MIN(a,b) ((a)<(b)?(a):(b))
+
+static wchar_t *twoway_wcsstr(const wchar_t *h, const wchar_t *n)
+{
+	const wchar_t *z;
+	size_t l, ip, jp, k, p, ms, p0, mem, mem0;
+
+	/* Computing length of needle */
+	for (l=0; n[l] && h[l]; l++);
+	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 (wmemcmp(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 wchar_t *z2 = wmemchr(z, 0, grow);
+			if (z2) {
+				z = z2;
+				if (z-h < l) return 0;
+			} else z += grow;
+		}
+
+		/* 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 (wchar_t *)h;
+		h += p;
+		mem = mem0;
+	}
+}
+
+wchar_t *wcsstr(const wchar_t *h, const wchar_t *n)
+{
+	/* Return immediately on empty needle or haystack */
+	if (!n[0]) return (wchar_t *)h;
+	if (!h[0]) return 0;
+
+	/* Use faster algorithms for short needles */
+	h = wcschr(h, *n);
+	if (!h || !n[1]) return (wchar_t *)h;
+	if (!h[1]) return 0;
+	if (!n[2] || !n[3] || !n[4]) return naive_wcsstr(h, n);
+
+	return twoway_wcsstr(h, n);
+}