# strncpy_PF.S

/* Copyright (c) 2006, Carlos Lamas

based on libc/pmstring/strncpy_P.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
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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
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. */

/* $Id$ */

#if !defined(__AVR_TINY__)

#include "macros.inc"

#define dest_b1 r25
#define dest_b0 r24
#define src_b3 r23
#define src_b2 r22
#define src_b1 r21
#define src_b0 r20
#define len_b1 r19
#define len_b0 r18

/** \ingroup avr_pgmspace
\fn char *strncpy_PF (char *dst, uint_farptr_t src, size_t n)
\brief Duplicate a string until a limited length

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

In the case where the length of \e src is less than that of \e n, the
remainder of \e dst will be padded with nulls

\param dst A pointer to the destination string in SRAM
\param src A far pointer to the source string in Flash
\param n The maximum number of bytes to copy

\returns The strncpy_PF() function returns a pointer to the destination
string \e dst. The contents of RAMPZ SFR are undefined when the function
returns */

#if !defined(__DOXYGEN__)

.text
.global _U(strncpy_PF)
.type   _U(strncpy_PF), @function

_U(strncpy_PF):

X_movw  ZL, src_b0
LPM_R0_ZPLUS_INIT src_b2
X_movw  XL, dest_b0

.L_strncpy_PF_loop:

subi    len_b0, lo8(1)
sbci    len_b1, hi8(1)
brcs    .L_strncpy_PF_done
LPM_R0_ZPLUS_NEXT src_b2
st      X+, r0
tst     r0
brne    .L_strncpy_PF_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_PF_clr_start

.L_strncpy_PF_clr_loop:

st      X+, __zero_reg__

.L_strncpy_PF_clr_start:

subi    len_b0, lo8(1)
sbci    len_b1, hi8(1)
brcc    .L_strncpy_PF_clr_loop

.L_strncpy_PF_done:
LPM_R0_ZPLUS_FINI src_b2
; return dest (unchanged)

ret

.L_strncpy_PF_end:

.size   _U(strncpy_PF), .L_strncpy_PF_end - _U(strncpy_PF)

#endif /* not __DOXYGEN__ */

#endif /* !defined(__AVR_TINY__) */