66 lines
2.2 KiB
C
66 lines
2.2 KiB
C
/****************************************************************************
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* libs/libc/string/lib_ffs.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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* Pre-processor Definitions
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****************************************************************************/
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#define NBITS (8 * sizeof(unsigned int))
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/****************************************************************************
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* Public Functions
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****************************************************************************/
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/****************************************************************************
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* Name: ffs
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*
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* Description:
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* The ffs() function will find the first bit set (beginning with the least
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* significant bit) in j, and return the index of that bit. Bits are
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* numbered starting at one (the least significant bit).
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*
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* Returned Value:
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* The ffs() function will return the index of the first bit set. If j is
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* 0, then ffs() will return 0.
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*
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****************************************************************************/
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int ffs(int 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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unsigned int value = (unsigned int)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) != 0)
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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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}
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return ret;
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}
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