94 lines
3.3 KiB
C
94 lines
3.3 KiB
C
|
/****************************************************************************
|
||
|
|
* libc/string/lib_fls.c
|
||
|
|
*
|
||
|
|
* Copyright (C) 2017 Haltian Ltd. All rights reserved.
|
||
|
|
* Author: Jussi Kivilinna <jussi.kivilinna@haltian.com>
|
||
|
|
*
|
||
|
|
* 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))
|
||
|
|
|
||
|
|
/****************************************************************************
|
||
|
|
* Public Functions
|
||
|
|
****************************************************************************/
|
||
|
|
|
||
|
|
/****************************************************************************
|
||
|
|
* Name: flsl
|
||
|
|
*
|
||
|
|
* Description:
|
||
|
|
* The flsl() function will find the last bit set in value and return
|
||
|
|
* the index of that bit. Bits are numbered starting at one (the least
|
||
|
|
* significant bit).
|
||
|
|
*
|
||
|
|
* Returned Value:
|
||
|
|
* The flsl() function will return the index of the last bit set. If j is
|
||
|
|
* 0, then flsl() will return 0.
|
||
|
|
*
|
||
|
|
****************************************************************************/
|
||
|
|
|
||
|
|
int flsl(long j)
|
||
|
|
{
|
||
|
|
int ret = 0;
|
||
|
|
|
||
|
|
if (j != 0)
|
||
|
|
{
|
||
|
|
#ifdef CONFIG_HAVE_BUILTIN_CLZ
|
||
|
|
/* Count leading zeros function can be used to implement fls. */
|
||
|
|
|
||
|
|
ret = NBITS - __builtin_clzl(j);
|
||
|
|
#else
|
||
|
|
unsigned long value = (unsigned long)j;
|
||
|
|
int bitno;
|
||
|
|
|
||
|
|
for (bitno = 1; bitno <= NBITS; bitno++, value >>= 1)
|
||
|
|
{
|
||
|
|
if (value == 1)
|
||
|
|
{
|
||
|
|
ret = bitno;
|
||
|
|
break;
|
||
|
|
}
|
||
|
|
}
|
||
|
|
#endif
|
||
|
|
}
|
||
|
|
|
||
|
|
return ret;
|
||
|
|
}
|