strncpy.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 char *strncpy(char *dest, const char *src, size_t len)
\brief Copy a string.

The strncpy() function is similar to strcpy(), except that not more than n
bytes of src are copied. Thus, if there is no null byte among the first n
bytes of src, the result will not be null-terminated.

In the case where the length of src is less than that of n, the remainder
of dest will be padded with nulls.

\returns The strncpy() function returns a pointer to the destination
string dest.  */

#if !defined(__DOXYGEN__)

#include "macros.inc"

#define dest_hi r25
#define dest_lo r24
#define src_hi r23
#define src_lo r22
#define len_hi r21
#define len_lo r20

ASSEMBLY_CLIB_SECTION
.global _U(strncpy)
.type   _U(strncpy), @function
_U(strncpy):
X_movw  ZL, src_lo
X_movw  XL, dest_lo
.L_strncpy_loop:
subi    len_lo, lo8(1)
sbci    len_hi, hi8(1)
brcs    .L_strncpy_done
ld      __tmp_reg__, Z+
st      X+, __tmp_reg__
tst     __tmp_reg__
brne    .L_strncpy_loop
; store null characters up to the end of dest
; as the glibc manual says:
; This behavior is rarely useful, but it is specified by the ISO C standard.
rjmp    .L_strncpy_clr_start
.L_strncpy_clr_loop:
st      X+, __zero_reg__
.L_strncpy_clr_start:
subi    len_lo, lo8(1)
sbci    len_hi, hi8(1)
brcc    .L_strncpy_clr_loop
.L_strncpy_done:
; return dest (unchanged)
ret
.L_strncpy_end:
.size   _U(strncpy), .L_strncpy_end - _U(strncpy)

#endif /* not __DOXYGEN__ */