1 files changed, 97 insertions, 0 deletions
diff --git a/lib/libc/stdlib/tsearch_path.h b/lib/libc/stdlib/tsearch_path.h
new file mode 100644
index 0000000..934c91f
--- /dev/null
+++ b/lib/libc/stdlib/tsearch_path.h
@@ -0,0 +1,97 @@
+/*-
+ * Copyright (c) 2015 Nuxi, https://nuxi.nl/
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
+ * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+ * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+ * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+ * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+ * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ *
+ * $FreeBSD$
+ */
+
+#ifndef TSEARCH_PATH_H
+#define	TSEARCH_PATH_H
+
+#include <limits.h>
+#include <stdbool.h>
+#include <stdint.h>
+
+/*
+ * Bookkeeping for storing a path in a balanced binary search tree from
+ * the root to a leaf node.
+ *
+ * For an AVL tree we know that its maximum height of a tree is bounded
+ * by approximately 1.44 * log2(n) - 0.328. Given that the number of
+ * entries of the tree is constrained by the size of the address space,
+ * two uintptr_t's provide sufficient space to store the path from the
+ * root to any leaf.
+ */
+struct path {
+	uintptr_t steps[2];
+	unsigned int nsteps;
+};
+
+/* Initializes the path structure with a zero-length path. */
+static inline void
+path_init(struct path *p)
+{
+
+	p->nsteps = 0;
+}
+
+#define	STEPS_BIT (sizeof(uintptr_t) * CHAR_BIT)
+
+/* Pushes a step to the left to the end of the path. */
+static inline void
+path_taking_left(struct path *p)
+{
+
+	p->steps[p->nsteps / STEPS_BIT] |=
+	    (uintptr_t)1 << (p->nsteps % STEPS_BIT);
+	++p->nsteps;
+}
+
+/* Pushes a step to the right to the end of the path. */
+static inline void
+path_taking_right(struct path *p)
+{
+
+	p->steps[p->nsteps / STEPS_BIT] &=
+	    ~((uintptr_t)1 << (p->nsteps % STEPS_BIT));
+	++p->nsteps;
+}
+
+/*
+ * Pops the first step from the path and returns whether it was a step
+ * to the left.
+ */
+static inline bool
+path_took_left(struct path *p)
+{
+	bool result;
+
+	result = p->steps[0] & 0x1;
+	p->steps[0] = (p->steps[0] >> 1) | (p->steps[1] << (STEPS_BIT - 1));
+	p->steps[1] >>= 1;
+	return (result);
+}
+
+#undef STEPS_BIT
+
+#endif