# memmem.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_string
\fn void *memmem(const void *s1, size_t len1, const void *s2, size_t len2)

The memmem() function finds the start of the first occurrence of the
substring \p s2 of length \p len2 in the memory area \p s1 of length
\p len1.

\return The memmem() function returns a pointer to the beginning of
the substring, or \c NULL if the substring is not found. If \p len2
is zero, the function returns \p s1.        */

/** \ingroup avr_pgmspace
\fn void *memmem_P(const void *s1, size_t len1, PGM_VOID_P s2, size_t len2)

The memmem_P() function is similar to memmem() except that \p s2 is
pointer to a string in program space.       */

#if !defined(__AVR_TINY__)

#if !defined(__DOXYGEN__)

#include "asmdef.h"

#define s1_hi   r25
#define s1_lo   r24
#define len1_hi r23
#define len1_lo r22
#define s2_hi   r21
#define s2_lo   r20
#define len2_hi r19
#define len2_lo r18

#define beg2    r17     /* begin of s2: s2[0]   */
#define c1      r16     /* char from s1[]       */
#define c2      r0      /* char from s2[]: tuned for classic lpm instr. */

#ifdef  Lprogmem
# define memmem  memmem_P
#else
#endif

ENTRY memmem
cp      len2_lo, __zero_reg__
cpc     len2_hi, __zero_reg__
breq    .L_ret                  ; s2[] is empty

push    beg2
push    c1

add     len2_lo, s2_lo          ; len2 = &(s2[len2])
add     len1_lo, s1_lo          ; len1 = &(s1[len1])

X_movw  ZL, s2_lo
LOAD    beg2, Z+                ; beg2 = s2[0]
X_movw  s2_lo, ZL               ; save: address of s2[1]

1:      X_movw  XL, s1_lo               ; goto to begin of s1[]

2:      cp      XL, len1_lo             ; find first char that is matched
cpc     XH, len1_hi
brsh    .L_nomatch
ld      c1, X+
cp      c1, beg2
brne    2b

X_movw  s1_lo, XL               ; store address

X_movw  ZL, s2_lo
3:      cp      ZL, len2_lo             ; compare strings
cpc     ZH, len2_hi
brsh    .L_match                ; end of s2[] --> OK
cp      XL, len1_lo
cpc     XH, len1_hi
brsh    .L_nomatch              ; s1[] tail is too short
ld      c1, X+
cp      c1, c2
breq    3b
rjmp    1b                      ; no equal

.L_nomatch:
ldi     s1_lo, lo8(1)
ldi     s1_hi, hi8(1)
.L_match:
sbiw    s1_lo, 1                ; restore after post-increment
pop     c1
pop     beg2
.L_ret:
ret

ENDFUNC

#endif /* not __DOXYGEN__ */

#endif /* !defined(__AVR_TINY__) */