strncmp.S

/* Copyright (c) 2002, 2007 Marek Michalkiewicz
   All rights reserved.

   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 int strncmp(const char *s1, const char *s2, size_t len)
    \brief Compare two strings.

    The strncmp() function is similar to strcmp(), except it only compares the
    first (at most) n characters of s1 and s2.

    \returns The strncmp() function returns an integer less than, equal to, or
    greater than zero if s1 (or the first n bytes thereof) is found,
    respectively, to be less than, to match, or be greater than s2.  */

#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(strncmp)
        .type   _U(strncmp), @function
_U(strncmp):
        X_movw  ZL, s2_lo
        X_movw  XL, s1_lo
.L_strncmp_loop:
        subi    len_lo, lo8(1)
        sbci    len_hi, hi8(1)
        brcs    .L_strncmp_equal
        ld      ret_lo, X+
        ld      __tmp_reg__, Z+
        sub     ret_lo, __tmp_reg__
        brne    .L_strncmp_done
        tst     __tmp_reg__
        brne    .L_strncmp_loop
.L_strncmp_equal:
        sub     ret_lo, ret_lo  ; clear ret_lo and C flag
.L_strncmp_done:
; ret_hi = SREG.C ? 0xFF : 0
        sbc     ret_hi, ret_hi
        ret
.L_strncmp_end:
        .size   _U(strncmp), .L_strncmp_end - _U(strncmp)

#endif /* not __DOXYGEN__ */