1 /*- 2 * Copyright (c) 2015 Nuxi, https://nuxi.nl/ 3 * 4 * Redistribution and use in source and binary forms, with or without 5 * modification, are permitted provided that the following conditions 6 * are met: 7 * 1. Redistributions of source code must retain the above copyright 8 * notice, this list of conditions and the following disclaimer. 9 * 2. Redistributions in binary form must reproduce the above copyright 10 * notice, this list of conditions and the following disclaimer in the 11 * documentation and/or other materials provided with the distribution. 12 * 13 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND 14 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 15 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 16 * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE 17 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 18 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 19 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 20 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 21 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 22 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 23 * SUCH DAMAGE. 24 */ 25 26 #ifndef TSEARCH_PATH_H 27 #define TSEARCH_PATH_H 28 29 #include <limits.h> 30 #include <stdbool.h> 31 #include <stdint.h> 32 33 /* 34 * Bookkeeping for storing a path in a balanced binary search tree from 35 * the root to a leaf node. 36 * 37 * For an AVL tree we know that its maximum height of a tree is bounded 38 * by approximately 1.44 * log2(n) - 0.328. Given that the number of 39 * entries of the tree is constrained by the size of the address space, 40 * two uintptr_t's provide sufficient space to store the path from the 41 * root to any leaf. 42 */ 43 struct path { 44 uintptr_t steps[2]; 45 unsigned int nsteps; 46 }; 47 48 /* Initializes the path structure with a zero-length path. */ 49 static inline void 50 path_init(struct path *p) 51 { 52 53 p->nsteps = 0; 54 } 55 56 #define STEPS_BIT (sizeof(uintptr_t) * CHAR_BIT) 57 58 /* Pushes a step to the left to the end of the path. */ 59 static inline void 60 path_taking_left(struct path *p) 61 { 62 63 p->steps[p->nsteps / STEPS_BIT] |= 64 (uintptr_t)1 << (p->nsteps % STEPS_BIT); 65 ++p->nsteps; 66 } 67 68 /* Pushes a step to the right to the end of the path. */ 69 static inline void 70 path_taking_right(struct path *p) 71 { 72 73 p->steps[p->nsteps / STEPS_BIT] &= 74 ~((uintptr_t)1 << (p->nsteps % STEPS_BIT)); 75 ++p->nsteps; 76 } 77 78 /* 79 * Pops the first step from the path and returns whether it was a step 80 * to the left. 81 */ 82 static inline bool 83 path_took_left(struct path *p) 84 { 85 bool result; 86 87 result = p->steps[0] & 0x1; 88 p->steps[0] = (p->steps[0] >> 1) | (p->steps[1] << (STEPS_BIT - 1)); 89 p->steps[1] >>= 1; 90 return (result); 91 } 92 93 #undef STEPS_BIT 94 95 #endif 96