/*-
* 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
