strnlen.S

/* Copyright (c) 2002, 2007 Marek Michalkiewicz

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
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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
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 size_t strnlen(const char *src, size_t len)
\brief Determine the length of a fixed-size string.

The strnlen function returns the number of characters in the string
pointed to by src, not including the terminating '\\0' character, but at
most len. In doing this, strnlen looks only at the first len characters at
src and never beyond src+len.

\returns The strnlen function returns strlen(src), if that is less than
len, or len if there is no '\\0' character among the first len
characters pointed to by src. */

#if !defined(__DOXYGEN__)

#include "macros.inc"

#define src_hi r25
#define src_lo r24
#define len_hi r23
#define len_lo r22

ASSEMBLY_CLIB_SECTION
.global _U(strnlen)
.type   _U(strnlen), @function
_U(strnlen):
X_movw  ZL, src_lo
.L_strnlen_loop:
subi    len_lo, lo8(1)
sbci    len_hi, hi8(1)
ld      __tmp_reg__, Z+
cpse    __tmp_reg__, __zero_reg__
brcc    .L_strnlen_loop
; Z points one character past the terminating NUL
; return Z - 1 - src = (-1 - src) + Z = ~src + Z
com     src_lo
com     src_hi