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> 13 #include <zephyr/arch/common/ffs.h> 14 #include <zephyr/sys/util.h> 15 16 /** 17 * @file 18 * @brief Provide ilog2() function 19 */ 20 21 /** 22 * 23 * @brief Calculate the floor of log2 for compile time constant 24 * 25 * This calculates the floor of log2 (integer log2) for 32-bit 26 * unsigned integer. 27 * 28 * @note This should only be used for compile time constant 29 * when value is known during preprocessing stage. 30 * DO NOT USE for runtime code due to the big tree of 31 * nested if-else blocks. 32 * 33 * @warning Will return 0 if input value is 0, which is 34 * invalid for log2. 35 * 36 * @param n Input value 37 * @return Integer log2 of @n 38 */ 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 75 /** 76 * 77 * @brief Calculate integer log2 78 * 79 * This calculates the floor of log2 (integer of log2). 80 * 81 * @warning Will return 0 if input value is 0, which is 82 * invalid for log2. 83 * 84 * @param n Input value 85 * @return Integer log2 of @p n 86 */ 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_ */ 101
