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