99 lines
3.4 KiB
C
99 lines
3.4 KiB
C
/****************************************************************************
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* libc/string/lib_fls.c
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*
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* Copyright (C) 2017 Haltian Ltd. All rights reserved.
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* Author: Jussi Kivilinna <jussi.kivilinna@haltian.com>
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions
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* are met:
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*
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* 1. Redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimer.
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* 2. Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in
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* the documentation and/or other materials provided with the
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* distribution.
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* 3. Neither the name NuttX nor the names of its contributors may be
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* used to endorse or promote products derived from this software
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* without specific prior written permission.
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*
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* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
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* "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
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* LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
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* FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
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* COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
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* INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
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* BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
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* OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
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* AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
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* ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
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* POSSIBILITY OF SUCH DAMAGE.
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*
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****************************************************************************/
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/****************************************************************************
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* Included Files
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****************************************************************************/
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#include <nuttx/compiler.h>
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#include <strings.h>
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/****************************************************************************
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* Pre-processor Definitions
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****************************************************************************/
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#define NBITS (8 * sizeof(unsigned long long))
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/****************************************************************************
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* Public Functions
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****************************************************************************/
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#ifdef CONFIG_HAVE_LONG_LONG
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/****************************************************************************
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* Name: flsll
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*
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* Description:
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* The flsll() function will find the last bit set in value and return
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* the index of that bit. Bits are numbered starting at one (the least
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* significant bit).
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*
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* Returned Value:
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* The flsll() function will return the index of the last bit set. If j is
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* 0, then flsll() will return 0.
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*
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****************************************************************************/
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int flsll(long long j)
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{
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int ret = 0;
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if (j != 0)
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{
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#ifdef CONFIG_HAVE_BUILTIN_CLZ
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/* Count leading zeros function can be used to implement fls. */
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ret = NBITS - __builtin_clzll(j);
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#else
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unsigned long long value = (unsigned long long)j;
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int bitno;
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for (bitno = 1; bitno <= NBITS; bitno++, value >>= 1)
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{
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if (value == 1)
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{
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ret = bitno;
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break;
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}
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}
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#endif
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}
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return ret;
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}
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#endif
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