nuttx/libc/string/lib_ffsll.c

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/****************************************************************************
* libc/string/lib_ffsll.c
*
* Copyright (C) 2017 Gregory Nutt. All rights reserved.
* Author: Gregory Nutt <gnutt@nuttx.org>
*
* 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 <nuttx/compiler.h>
#include <strings.h>
/****************************************************************************
* Pre-processor Definitions
****************************************************************************/
#define NBITS (8 * sizeof(unsigned long long))
/****************************************************************************
* Public Functions
****************************************************************************/
#ifdef CONFIG_HAVE_LONG_LONG
/****************************************************************************
* Name: ffsll
*
* Description:
* The ffsll() 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 ffsll() function will return the index of the first bit set. If j is
* 0, then ffsll() will return 0.
*
****************************************************************************/
int ffsll(long long j)
{
int ret = 0;
if (j != 0)
{
#ifdef CONFIG_HAVE_BUILTIN_CTZ
/* Count trailing zeros function can be used to implement ffs. */
ret = __builtin_ctzll(j) + 1;
#else
unsigned long long value = (unsigned long long)j;
int bitno;
for (bitno = 1; bitno <= NBITS; bitno++, value >>= 1)
{
if ((value & 1) != 0)
{
ret = bitno;
break;
}
}
#endif
}
return ret;
}
#endif