gbdk-2020 | GameBoy Development Kit |
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gbdk-lib/libc/asm/z80/strlen.s
1 ;--------------------------------------------------------------------------
2 ; strlen.s
3 ;
4 ; Copyright (C) 2008-2009, Philipp Klaus Krause
5 ;
6 ; This library is free software; you can redistribute it and/or modify it
7 ; under the terms of the GNU General Public License as published by the
8 ; Free Software Foundation; either version 2, or (at your option) any
9 ; later version.
10 ;
11 ; This library is distributed in the hope that it will be useful,
12 ; but WITHOUT ANY WARRANTY; without even the implied warranty of
13 ; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
14 ; GNU General Public License for more details.
15 ;
16 ; You should have received a copy of the GNU General Public License
17 ; along with this library; see the file COPYING. If not, write to the
18 ; Free Software Foundation, 51 Franklin Street, Fifth Floor, Boston,
19 ; MA 02110-1301, USA.
20 ;
21 ; As a special exception, if you link this library with other files,
22 ; some of which are compiled with SDCC, to produce an executable,
23 ; this library does not by itself cause the resulting executable to
24 ; be covered by the GNU General Public License. This exception does
25 ; not however invalidate any other reasons why the executable file
26 ; might be covered by the GNU General Public License.
27 ;--------------------------------------------------------------------------
28
29 .area _CODE
30
31 .globl _strlen
32
33 ; The Z80 has the cpir instruction, which is perfect for implementing strlen().
34
35 _strlen:
36 pop bc
37 pop hl
38 push hl
39 push bc
40 xor a, a
41 ld b, a
42 ld c, a
43 cpir
44 ld hl, #-1
45 sbc hl, bc ; C flag still cleared from xor above.
46 ret
47
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