memrchr_P.S

/* Copyright (c) 2007  Dmitry Xmelkov
   All rights reserved.

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     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
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/* $Id$ */

/** \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
        adiw    ZL, 0
        breq    2f                      ; len is 0, return NULL
        add     ZL, src_lo
        adc     ZH, src_hi

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__) */