gbdk-2020 | GameBoy Development Kit |
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gbdk-lib/libc/asm/z80/__strreverse.s
1 ;--------------------------------------------------------------------------
2 ; __strreverse.s
3 ;
4 ; Copyright (C) 2020, Sergey Belyashov
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 ___strreverse
32 .globl ___strreverse_reg
33 ;
34 ;char * __reverse(char *beg, char *end);
35 ;
36 ___strreverse::
37 pop bc
38 pop de
39 pop hl
40 push hl
41 push de
42 push bc
43
44 ;in: HL - pointer to end of string (null symbol), DE - pointer to start of string
45 ;
46 ___strreverse_reg::
47 push de
48 jr 110$
49 100$:
50 add hl, de
51 ld a, (de)
52 ld c, (hl)
53 ld (hl), a
54 ld a, c
55 ld (de), a
56 inc de
57 110$:
58 dec hl
59 or a, a
60 sbc hl, de
61 jr NC, 100$
62 pop hl
63 ret
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