1 files changed, 92 insertions, 0 deletions
diff --git a/src/search/tsearch.c b/src/search/tsearch.c
new file mode 100644
index 00000000..0de27d05
--- /dev/null
+++ b/src/search/tsearch.c
@@ -0,0 +1,92 @@
+#include <stdlib.h>
+#include <search.h>
+#include "tsearch.h"
+
+static inline int height(struct node *n) { return n ? n->h : 0; }
+
+static int rot(void **p, struct node *x, int dir /* deeper side */)
+{
+	struct node *y = x->a[dir];
+	struct node *z = y->a[!dir];
+	int hx = x->h;
+	int hz = height(z);
+	if (hz > height(y->a[dir])) {
+		/*
+		 *   x
+		 *  / \ dir          z
+		 * A   y            / \
+		 *    / \   -->    x   y
+		 *   z   D        /|   |\
+		 *  / \          A B   C D
+		 * B   C
+		 */
+		x->a[dir] = z->a[!dir];
+		y->a[!dir] = z->a[dir];
+		z->a[!dir] = x;
+		z->a[dir] = y;
+		x->h = hz;
+		y->h = hz;
+		z->h = hz+1;
+	} else {
+		/*
+		 *   x               y
+		 *  / \             / \
+		 * A   y    -->    x   D
+		 *    / \         / \
+		 *   z   D       A   z
+		 */
+		x->a[dir] = z;
+		y->a[!dir] = x;
+		x->h = hz+1;
+		y->h = hz+2;
+		z = y;
+	}
+	*p = z;
+	return z->h - hx;
+}
+
+/* balance *p, return 0 if height is unchanged.  */
+int __tsearch_balance(void **p)
+{
+	struct node *n = *p;
+	int h0 = height(n->a[0]);
+	int h1 = height(n->a[1]);
+	if (h0 - h1 + 1u < 3u) {
+		int old = n->h;
+		n->h = h0<h1 ? h1+1 : h0+1;
+		return n->h - old;
+	}
+	return rot(p, n, h0<h1);
+}
+
+void *tsearch(const void *key, void **rootp,
+	int (*cmp)(const void *, const void *))
+{
+	if (!rootp)
+		return 0;
+
+	void **a[MAXH];
+	struct node *n = *rootp;
+	struct node *r;
+	int i=0;
+	a[i++] = rootp;
+	for (;;) {
+		if (!n)
+			break;
+		int c = cmp(key, n->key);
+		if (!c)
+			return n;
+		a[i++] = &n->a[c>0];
+		n = n->a[c>0];
+	}
+	r = malloc(sizeof *r);
+	if (!r)
+		return 0;
+	r->key = key;
+	r->a[0] = r->a[1] = 0;
+	r->h = 1;
+	/* insert new node, rebalance ancestors.  */
+	*a[--i] = r;
+	while (i && __tsearch_balance(a[--i]));
+	return r;
+}