| 1 | /* SPDX-License-Identifier: LGPL-2.1-or-later */ |
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| 2 | /* |
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| 3 | * Provides fixed-point logarithm operations. |
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| 4 | * |
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| 5 | * Copyright (C) 2006 Christoph Pfister (christophpfister@gmail.com) |
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| 6 | */ |
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| 7 | |
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| 8 | #ifndef __LINUX_INT_LOG_H |
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| 9 | #define __LINUX_INT_LOG_H |
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| 10 | |
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| 11 | #include <linux/types.h> |
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| 12 | |
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| 13 | /** |
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| 14 | * intlog2 - computes log2 of a value; the result is shifted left by 24 bits |
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| 15 | * |
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| 16 | * @value: The value (must be != 0) |
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| 17 | * |
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| 18 | * to use rational values you can use the following method: |
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| 19 | * |
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| 20 | * intlog2(value) = intlog2(value * 2^x) - x * 2^24 |
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| 21 | * |
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| 22 | * Some usecase examples: |
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| 23 | * |
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| 24 | * intlog2(8) will give 3 << 24 = 3 * 2^24 |
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| 25 | * |
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| 26 | * intlog2(9) will give 3 << 24 + ... = 3.16... * 2^24 |
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| 27 | * |
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| 28 | * intlog2(1.5) = intlog2(3) - 2^24 = 0.584... * 2^24 |
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| 29 | * |
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| 30 | * |
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| 31 | * return: log2(value) * 2^24 |
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| 32 | */ |
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| 33 | extern unsigned int intlog2(u32 value); |
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| 34 | |
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| 35 | /** |
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| 36 | * intlog10 - computes log10 of a value; the result is shifted left by 24 bits |
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| 37 | * |
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| 38 | * @value: The value (must be != 0) |
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| 39 | * |
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| 40 | * to use rational values you can use the following method: |
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| 41 | * |
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| 42 | * intlog10(value) = intlog10(value * 10^x) - x * 2^24 |
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| 43 | * |
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| 44 | * An usecase example: |
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| 45 | * |
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| 46 | * intlog10(1000) will give 3 << 24 = 3 * 2^24 |
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| 47 | * |
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| 48 | * due to the implementation intlog10(1000) might be not exactly 3 * 2^24 |
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| 49 | * |
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| 50 | * look at intlog2 for similar examples |
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| 51 | * |
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| 52 | * return: log10(value) * 2^24 |
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| 53 | */ |
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| 54 | extern unsigned int intlog10(u32 value); |
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| 55 | |
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| 56 | #endif |
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| 57 | |
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