96 lines
2.6 KiB
C
96 lines
2.6 KiB
C
/*
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* Copyright (c) 2021 Intel Corporation
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*
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* SPDX-License-Identifier: Apache-2.0
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*/
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#include <stdint.h>
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#include <toolchain.h>
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#include <arch/common/ffs.h>
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#include <sys/util.h>
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/**
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* @file
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* @brief Provide ilog2() function
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*/
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/**
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* @def ilog2_compile_time_const_u32(n)
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* @brief Calculate the floor of log2 for compile time constant
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*
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* This calculates the floor of log2 (integer log2) for 32-bit
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* unsigned integer.
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*
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* @note This should only be used for compile time constant
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* when value is known during preprocessing stage.
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* DO NOT USE for runtime code due to the big tree of
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* nested if-else blocks.
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*
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* @warning Will return 0 if input value is 0, which is
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* invalid for log2.
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*
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* @param n Input value
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* @return Integer log2 of @n
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*/
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#define ilog2_compile_time_const_u32(n) \
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( \
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(n < 2) ? 0 : \
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((n & BIT(31)) == BIT(31)) ? 31 : \
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((n & BIT(30)) == BIT(30)) ? 30 : \
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((n & BIT(29)) == BIT(29)) ? 29 : \
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((n & BIT(28)) == BIT(28)) ? 28 : \
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((n & BIT(27)) == BIT(27)) ? 27 : \
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((n & BIT(26)) == BIT(26)) ? 26 : \
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((n & BIT(25)) == BIT(25)) ? 25 : \
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((n & BIT(24)) == BIT(24)) ? 24 : \
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((n & BIT(23)) == BIT(23)) ? 23 : \
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((n & BIT(22)) == BIT(22)) ? 22 : \
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((n & BIT(21)) == BIT(21)) ? 21 : \
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((n & BIT(20)) == BIT(20)) ? 20 : \
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((n & BIT(19)) == BIT(19)) ? 19 : \
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((n & BIT(18)) == BIT(18)) ? 18 : \
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((n & BIT(17)) == BIT(17)) ? 17 : \
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((n & BIT(16)) == BIT(16)) ? 16 : \
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((n & BIT(15)) == BIT(15)) ? 15 : \
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((n & BIT(14)) == BIT(14)) ? 14 : \
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((n & BIT(13)) == BIT(13)) ? 13 : \
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((n & BIT(12)) == BIT(12)) ? 12 : \
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((n & BIT(11)) == BIT(11)) ? 11 : \
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((n & BIT(10)) == BIT(10)) ? 10 : \
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((n & BIT(9)) == BIT(9)) ? 9 : \
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((n & BIT(8)) == BIT(8)) ? 8 : \
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((n & BIT(7)) == BIT(7)) ? 7 : \
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((n & BIT(6)) == BIT(6)) ? 6 : \
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((n & BIT(5)) == BIT(5)) ? 5 : \
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((n & BIT(4)) == BIT(4)) ? 4 : \
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((n & BIT(3)) == BIT(3)) ? 3 : \
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((n & BIT(2)) == BIT(2)) ? 2 : \
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1 \
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)
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/**
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* @def ilog2(n)
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* @brief Calculate integer log2
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*
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* This calculates the floor of log2 (integer of log2).
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*
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* @warning Will return 0 if input value is 0, which is
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* invalid for log2.
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*
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* @param n Input value
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* @return Integer log2 of @p n
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*/
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/*
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* This is in #define form as this needs to also work on
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* compile time constants. Doing this as a static inline
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* function will result in compiler complaining with
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* "initializer element is not constant".
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*/
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#define ilog2(n) \
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( \
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__builtin_constant_p(n) ? \
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ilog2_compile_time_const_u32(n) : \
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find_msb_set(n) - 1 \
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)
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