# strnlen_P.S

/* Copyright (c) 2005, 2006, 2007 Helmut Wallner

based on libc/string/strnlen.S which is

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_pgmspace
\fn size_t strnlen_P(PGM_P src, size_t len)
\brief Determine the length of a fixed-size string.

The strnlen_P() function is similar to strnlen(), except that \c src is a
pointer to a string in program space.

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

#if !defined(__AVR_TINY__)

#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_P)
.type   _U(strnlen_P), @function
_U(strnlen_P):
X_movw  ZL, src_lo
.L_strnlen_P_loop:
X_lpm   r0, Z+
subi    len_lo, lo8(1)
sbci    len_hi, hi8(1)
cpse    r0, __zero_reg__
brcc    .L_strnlen_P_loop
; Z points one character past the terminating NUL
; return Z - 1 - src = (-1 - src) + Z = ~src + Z
com     src_lo
com     src_hi