ilog2.h

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/*
 * Copyright (c) 2021 Intel Corporation
 *
 * SPDX-License-Identifier: Apache-2.0
 */
 
#ifndef ZEPHYR_INCLUDE_MATH_ILOG2_H_
#define ZEPHYR_INCLUDE_MATH_ILOG2_H_
 
#include <stdint.h>
 
#include <zephyr/toolchain.h>
#include <zephyr/arch/common/ffs.h>
#include <zephyr/sys/util.h>
 
#define ilog2_compile_time_const_u32(n)                 \
        (                                               \
                ((n) < 2) ? 0 :                         \
                (((n) & BIT(31)) == BIT(31)) ? 31 :     \
                (((n) & BIT(30)) == BIT(30)) ? 30 :     \
                (((n) & BIT(29)) == BIT(29)) ? 29 :     \
                (((n) & BIT(28)) == BIT(28)) ? 28 :     \
                (((n) & BIT(27)) == BIT(27)) ? 27 :     \
                (((n) & BIT(26)) == BIT(26)) ? 26 :     \
                (((n) & BIT(25)) == BIT(25)) ? 25 :     \
                (((n) & BIT(24)) == BIT(24)) ? 24 :     \
                (((n) & BIT(23)) == BIT(23)) ? 23 :     \
                (((n) & BIT(22)) == BIT(22)) ? 22 :     \
                (((n) & BIT(21)) == BIT(21)) ? 21 :     \
                (((n) & BIT(20)) == BIT(20)) ? 20 :     \
                (((n) & BIT(19)) == BIT(19)) ? 19 :     \
                (((n) & BIT(18)) == BIT(18)) ? 18 :     \
                (((n) & BIT(17)) == BIT(17)) ? 17 :     \
                (((n) & BIT(16)) == BIT(16)) ? 16 :     \
                (((n) & BIT(15)) == BIT(15)) ? 15 :     \
                (((n) & BIT(14)) == BIT(14)) ? 14 :     \
                (((n) & BIT(13)) == BIT(13)) ? 13 :     \
                (((n) & BIT(12)) == BIT(12)) ? 12 :     \
                (((n) & BIT(11)) == BIT(11)) ? 11 :     \
                (((n) & BIT(10)) == BIT(10)) ? 10 :     \
                (((n) & BIT(9)) == BIT(9)) ? 9 :        \
                (((n) & BIT(8)) == BIT(8)) ? 8 :        \
                (((n) & BIT(7)) == BIT(7)) ? 7 :        \
                (((n) & BIT(6)) == BIT(6)) ? 6 :        \
                (((n) & BIT(5)) == BIT(5)) ? 5 :        \
                (((n) & BIT(4)) == BIT(4)) ? 4 :        \
                (((n) & BIT(3)) == BIT(3)) ? 3 :        \
                (((n) & BIT(2)) == BIT(2)) ? 2 :        \
                1                                       \
        )
 
/*
 * This is in #define form as this needs to also work on
 * compile time constants. Doing this as a static inline
 * function will result in compiler complaining with
 * "initializer element is not constant".
 */
#define ilog2(n)                                        \
        (                                               \
                __builtin_constant_p(n) ?               \
                ilog2_compile_time_const_u32(n) :       \
                find_msb_set(n) - 1                     \
        )
 
#endif /* ZEPHYR_INCLUDE_MATH_ILOG2_H_ */