mirror of
https://github.com/freebsd/freebsd-src
synced 2024-07-23 03:06:48 +00:00
96 lines
2.8 KiB
C
96 lines
2.8 KiB
C
/*-
|
|
* 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.
|
|
*/
|
|
|
|
#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
|