# ffs.S

/* Copyright (c) 2005, 2007 Dmitry Xmelkov

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ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
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ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
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/* $Id$ */

/** \file */

/** \ingroup avr_string
\fn int ffs (int val);

\brief This function finds the first (least significant) bit set in the input value.

\returns The ffs() function returns the position of the first
(least significant) bit set in the word val, or 0 if no bits are set.
The least significant bit is position 1.

\note For expressions that are constant at compile time, consider
using the \ref _FFS macro instead.
*/

#ifndef __DOXYGEN__

#include "macros.inc"

#define val_lo  r24
#define val_hi  r25
#define cntr    r30

ASSEMBLY_CLIB_SECTION
.global     _U(ffs)
.type       _U(ffs), @function
_U(ffs):

ldi     cntr, 1
tst     val_lo
brne    2f
or      val_lo, val_hi
breq    9f
ldi     cntr, 8
1:      inc     cntr
2:      ror     val_lo
brcc    1b
mov     r24, cntr
clr     r25
9:      ret

.size  _U(ffs), . - _U(ffs)
.end
#endif  /* not __DOXYGEN__ */