79 lines
2.5 KiB
C
79 lines
2.5 KiB
C
/****************************************************************************
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* libs/libc/string/lib_flsl.c
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*
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* Licensed to the Apache Software Foundation (ASF) under one or more
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* contributor license agreements. See the NOTICE file distributed with
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* this work for additional information regarding copyright ownership. The
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* ASF licenses this file to you under the Apache License, Version 2.0 (the
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* "License"); you may not use this file except in compliance with the
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* License. You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
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* WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
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* License for the specific language governing permissions and limitations
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* under the License.
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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))
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/****************************************************************************
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* Public Functions
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****************************************************************************/
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/****************************************************************************
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* Name: flsl
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*
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* Description:
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* The flsl() 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 flsl() function will return the index of the last bit set. If j is
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* 0, then flsl() will return 0.
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*
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****************************************************************************/
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int flsl(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_clzl(j);
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#else
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unsigned long value = (unsigned 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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