Zephyr API Documentation  3.6.99
A Scalable Open Source RTOS
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ilog2.h
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1/*
2 * Copyright (c) 2021 Intel Corporation
3 *
4 * SPDX-License-Identifier: Apache-2.0
5 */
6
7#ifndef ZEPHYR_INCLUDE_MATH_ILOG2_H_
8#define ZEPHYR_INCLUDE_MATH_ILOG2_H_
9
10#include <stdint.h>
11
12#include <zephyr/toolchain.h>
14#include <zephyr/sys/util.h>
15
39#define ilog2_compile_time_const_u32(n) \
40 ( \
41 ((n) < 2) ? 0 : \
42 (((n) & BIT(31)) == BIT(31)) ? 31 : \
43 (((n) & BIT(30)) == BIT(30)) ? 30 : \
44 (((n) & BIT(29)) == BIT(29)) ? 29 : \
45 (((n) & BIT(28)) == BIT(28)) ? 28 : \
46 (((n) & BIT(27)) == BIT(27)) ? 27 : \
47 (((n) & BIT(26)) == BIT(26)) ? 26 : \
48 (((n) & BIT(25)) == BIT(25)) ? 25 : \
49 (((n) & BIT(24)) == BIT(24)) ? 24 : \
50 (((n) & BIT(23)) == BIT(23)) ? 23 : \
51 (((n) & BIT(22)) == BIT(22)) ? 22 : \
52 (((n) & BIT(21)) == BIT(21)) ? 21 : \
53 (((n) & BIT(20)) == BIT(20)) ? 20 : \
54 (((n) & BIT(19)) == BIT(19)) ? 19 : \
55 (((n) & BIT(18)) == BIT(18)) ? 18 : \
56 (((n) & BIT(17)) == BIT(17)) ? 17 : \
57 (((n) & BIT(16)) == BIT(16)) ? 16 : \
58 (((n) & BIT(15)) == BIT(15)) ? 15 : \
59 (((n) & BIT(14)) == BIT(14)) ? 14 : \
60 (((n) & BIT(13)) == BIT(13)) ? 13 : \
61 (((n) & BIT(12)) == BIT(12)) ? 12 : \
62 (((n) & BIT(11)) == BIT(11)) ? 11 : \
63 (((n) & BIT(10)) == BIT(10)) ? 10 : \
64 (((n) & BIT(9)) == BIT(9)) ? 9 : \
65 (((n) & BIT(8)) == BIT(8)) ? 8 : \
66 (((n) & BIT(7)) == BIT(7)) ? 7 : \
67 (((n) & BIT(6)) == BIT(6)) ? 6 : \
68 (((n) & BIT(5)) == BIT(5)) ? 5 : \
69 (((n) & BIT(4)) == BIT(4)) ? 4 : \
70 (((n) & BIT(3)) == BIT(3)) ? 3 : \
71 (((n) & BIT(2)) == BIT(2)) ? 2 : \
72 1 \
73 )
74
87/*
88 * This is in #define form as this needs to also work on
89 * compile time constants. Doing this as a static inline
90 * function will result in compiler complaining with
91 * "initializer element is not constant".
92 */
93#define ilog2(n) \
94 ( \
95 __builtin_constant_p(n) ? \
96 ilog2_compile_time_const_u32(n) : \
97 find_msb_set(n) - 1 \
98 )
99
100#endif /* ZEPHYR_INCLUDE_MATH_ILOG2_H_ */
Macros to abstract toolchain specific capabilities.
Misc utilities.