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