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9ab04d7e | 1 | /* SPDX-License-Identifier: LGPL-2.1-or-later */ |
da22d0e7 | 2 | /* |
f97fa3dc | 3 | * Provides fixed-point logarithm operations. |
da22d0e7 CP |
4 | * |
5 | * Copyright (C) 2006 Christoph Pfister (christophpfister@gmail.com) | |
da22d0e7 CP |
6 | */ |
7 | ||
f97fa3dc AS |
8 | #ifndef __LINUX_INT_LOG_H |
9 | #define __LINUX_INT_LOG_H | |
da22d0e7 CP |
10 | |
11 | #include <linux/types.h> | |
12 | ||
13 | /** | |
e383ce07 | 14 | * intlog2 - computes log2 of a value; the result is shifted left by 24 bits |
e08bb6f7 MCC |
15 | * |
16 | * @value: The value (must be != 0) | |
da22d0e7 CP |
17 | * |
18 | * to use rational values you can use the following method: | |
5b8700e9 | 19 | * |
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20 | * intlog2(value) = intlog2(value * 2^x) - x * 2^24 |
21 | * | |
dc2c8bd3 | 22 | * Some usecase examples: |
5b8700e9 | 23 | * |
dc2c8bd3 | 24 | * intlog2(8) will give 3 << 24 = 3 * 2^24 |
5b8700e9 | 25 | * |
dc2c8bd3 | 26 | * intlog2(9) will give 3 << 24 + ... = 3.16... * 2^24 |
5b8700e9 | 27 | * |
dc2c8bd3 | 28 | * intlog2(1.5) = intlog2(3) - 2^24 = 0.584... * 2^24 |
da22d0e7 | 29 | * |
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30 | * |
31 | * return: log2(value) * 2^24 | |
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32 | */ |
33 | extern unsigned int intlog2(u32 value); | |
34 | ||
35 | /** | |
e08bb6f7 MCC |
36 | * intlog10 - computes log10 of a value; the result is shifted left by 24 bits |
37 | * | |
38 | * @value: The value (must be != 0) | |
da22d0e7 CP |
39 | * |
40 | * to use rational values you can use the following method: | |
5b8700e9 | 41 | * |
da22d0e7 CP |
42 | * intlog10(value) = intlog10(value * 10^x) - x * 2^24 |
43 | * | |
dc2c8bd3 | 44 | * An usecase example: |
5b8700e9 | 45 | * |
dc2c8bd3 | 46 | * intlog10(1000) will give 3 << 24 = 3 * 2^24 |
5b8700e9 | 47 | * |
da22d0e7 CP |
48 | * due to the implementation intlog10(1000) might be not exactly 3 * 2^24 |
49 | * | |
50 | * look at intlog2 for similar examples | |
51 | * | |
e08bb6f7 | 52 | * return: log10(value) * 2^24 |
da22d0e7 CP |
53 | */ |
54 | extern unsigned int intlog10(u32 value); | |
55 | ||
56 | #endif |