43 lines
1007 B
C
43 lines
1007 B
C
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/*
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* Copyright (c) 2006-2021, RT-Thread Development Team
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*
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* SPDX-License-Identifier: Apache-2.0
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*
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* Change Logs:
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* Date Author Notes
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* 2024-06-21 Zhangyan first version
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*/
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#include <rthw.h>
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#include <rtthread.h>
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#include <board.h>
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#ifdef RT_USING_CPU_FFS
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/**
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* This function finds the first bit set (beginning with the least significant bit)
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* in value and return the index of that bit.
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*
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* Bits are numbered starting at 1 (the least significant bit). A return value of
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* zero from any of these functions means that the argument was zero.
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*
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* @return return the index of the first bit set. If value is 0, then this function
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* shall return 0.
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*/
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int __rt_ffs(int value)
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{
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#ifdef __GNUC__
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return __builtin_ffs(value);
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#else
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__asm__ volatile (
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"rbit w1, %w0\n"
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"cmp %w0, 0\n"
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"clz w1, w1\n"
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"csinc %w0, wzr, w1, eq\n"
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: "=r"(value)
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: "0"(value)
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);
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return value;
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#endif
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}
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#endif /* RT_USING_CPU_FFS */
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