# memcmp.S

/* Copyright (c) 2002, 2007 Marek Michalkiewicz

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modification, are permitted provided that the following conditions are met:

* Redistributions of source code must retain the above copyright
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* Redistributions in binary form must reproduce the above copyright
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the documentation and/or other materials provided with the
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* 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
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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 int memcmp(const void *s1, const void *s2, size_t len)
\brief Compare memory areas

The memcmp() function compares the first len bytes of the memory areas s1
and s2. The comparision is performed using unsigned char operations.

\returns The memcmp() function returns an integer less than, equal to, or
greater than zero if the first len bytes of s1 is found, respectively, to be
less than, to match, or be greater than the first len bytes of s2.

\note Be sure to store the result in a 16 bit variable since you may get
incorrect results if you use an unsigned char or char due to truncation.

\warning This function is not -mint8 compatible, although if you only care
about testing for equality, this function should be safe to use. */

#if !defined(__DOXYGEN__)

#include "macros.inc"

#define s1_hi r25
#define s1_lo r24
#define s2_hi r23
#define s2_lo r22
#define len_hi r21
#define len_lo r20

#define ret_hi r25
#define ret_lo r24

ASSEMBLY_CLIB_SECTION
.global _U(memcmp)
.type   _U(memcmp), @function
_U(memcmp):
X_movw  ZL, s2_lo
X_movw  XL, s1_lo
rjmp    .L_memcmp_start
.L_memcmp_loop:
ld      ret_lo, X+
ld      __tmp_reg__, Z+
sub     ret_lo, __tmp_reg__
brne    .L_memcmp_done
.L_memcmp_start:
subi    len_lo, lo8(1)
sbci    len_hi, hi8(1)
brcc    .L_memcmp_loop
; strings are equal, so clear both ret_lo and carry
sub     ret_lo, ret_lo
.L_memcmp_done:
; ret_hi = SREG.C ? 0xFF : 0
sbc     ret_hi, ret_hi
ret
.L_memcmp_end:
.size   _U(memcmp), .L_memcmp_end - _U(memcmp)

#endif /* not __DOXYGEN__ */