gbdk-2020 | GameBoy Development Kit |
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gbdk-lib/libc/asm/mos6502/_strlen.s
1 ;-------------------------------------------------------------------------
2 ; _strlen.s - standard C library function
3 ;
4 ; Copyright (C) 1998, Ullrich von Bassewitz
5 ; Copyright (C) 2023, Gabriele Gorla
6 ;
7 ; This library is free software; you can redistribute it and/or modify it
8 ; under the terms of the GNU General Public License as published by the
9 ; Free Software Foundation; either version 2, or (at your option) any
10 ; later version.
11 ;
12 ; This library is distributed in the hope that it will be useful,
13 ; but WITHOUT ANY WARRANTY; without even the implied warranty of
14 ; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
15 ; GNU General Public License for more details.
16 ;
17 ; You should have received a copy of the GNU General Public License
18 ; along with this library; see the file COPYING. If not, write to the
19 ; Free Software Foundation, 51 Franklin Street, Fifth Floor, Boston,
20 ; MA 02110-1301, USA.
21 ;
22 ; As a special exception, if you link this library with other files,
23 ; some of which are compiled with SDCC, to produce an executable,
24 ; this library does not by itself cause the resulting executable to
25 ; be covered by the GNU General Public License. This exception does
26 ; not however invalidate any other reasons why the executable file
27 ; might be covered by the GNU General Public License.
28 ;-------------------------------------------------------------------------
29
30 .module _strlen
31
32 ;--------------------------------------------------------
33 ; exported symbols
34 ;--------------------------------------------------------
35 .globl _strlen
36
37 ;--------------------------------------------------------
38 ; local aliases
39 ;--------------------------------------------------------
40 .define _src "DPTR"
41
42 ;--------------------------------------------------------
43 ; code
44 ;--------------------------------------------------------
45 .area _CODE
46
47 _strlen:
48 sta *_src+0
49 stx *_src+1
50
51 ldy #0x00
52 ldx #0x00
53 loop:
54 lda [_src],y
55 beq end
56 iny
57 bne loop
58 inc *_src+1
59 inx
60 bne loop
61 end:
62 tya
63 rts
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