gbdk-2020 | GameBoy Development Kit |
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gbdk-lib/libc/asm/sm83/crt0_rle.s
1 ;--------------------------------------------------------------------------
2 ; __initrleblock.s
3 ;
4 ; Copyright (C) 2001, Michael Hope
5 ; Copyright (C) 2020, Sergey Belyashov
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 rledecompress
31
32 .area _HOME
33
34 ;; Special RLE decoder used for initing global data
35 ;; input: DE - destination address
36 __initrleblock::
37 ;; Pop the return address
38 pop hl
39 1$:
40 ;; Fetch the run
41 ld c, (hl)
42 inc hl
43 ;; Negative means a run
44 bit 7, c
45 jr Z, 2$
46 ;; Expanding a run
47 ld a, (hl+)
48 3$:
49 ld (de), a
50 inc de
51 inc c
52 jr NZ, 3$
53 jr 1$
54 2$:
55 ;; Zero means end of a block
56 inc c
57 dec c
58 jr Z, 4$
59 ;; Expanding a block
60 5$:
61 ld a, (hl+)
62 ld (de), a
63 inc de
64 dec c
65 jr NZ, 5$
66 jr 1$
67 4$:
68 ;; Return back
69 jp (hl)
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