# memrchr_P.S

/* Copyright (c) 2007  Dmitry Xmelkov

Redistribution and use in source and binary forms, with or without
modification, are permitted provided that the following conditions are met:

* Redistributions of source code must retain the above copyright
notice, this list of conditions and the following disclaimer.
* 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.
* Neither the name of the copyright holders nor the names of
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. */

/* $Id$ */

/** \file */
/** \ingroup avr_pgmspace
\fn PGM_VOID_P memrchr_P(PGM_VOID_P src, int val, size_t len)

The memrchr_P() function is like the memchr_P() function, except
that it searches backwards from the end of the \p len bytes pointed
to by \p src instead of forwards from the front. (Glibc, GNU extension.)

\return The memrchr_P() function returns a pointer to the matching
byte or \c NULL if the character does not occur in the given memory
area.       */

#if !defined(__AVR_TINY__)

#if !defined(__DOXYGEN__)

#include "asmdef.h"

#define src_hi  r25
#define src_lo  r24
#define val     r22
#define len_hi  r21
#define len_lo  r20

#define ret_lo  r24

ENTRY memrchr_P
X_movw  ZL, len_lo
breq    2f                      ; len is 0, return NULL

1:      sbiw    ZL, 1
lpm
cp      r0, val
breq    2f                      ; val is found
subi    len_lo, lo8(1)
sbci    len_hi, hi8(1)
brne    1b

X_movw  ZL, len_lo              ; is zero
2:      X_movw  ret_lo, ZL
ret
ENDFUNC

#endif /* not __DOXYGEN__ */

#endif /*!defined(__AVR_TINY__) */