gbdk-2020 | GameBoy Development Kit |
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gbdk-lib/libc/asm/mos6502/abs.s
1 ;-------------------------------------------------------------------------
2 ; abs.s - standard C library function
3 ;
4 ; Copyright (C) 2023, Gabriele Gorla
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 .module _abs
30
31 ;--------------------------------------------------------
32 ; exported symbols
33 ;--------------------------------------------------------
34 .globl _abs
35 .globl ___negax
36
37 ;--------------------------------------------------------
38 ; code
39 ;--------------------------------------------------------
40
41 .area _CODE
42 _abs:
43 cpx #0x00
44 bpl skip
45 ___negax:
46 sec
47 eor #0xff
48 adc #0x00
49 pha
50 txa
51 eor #0xff
52 adc #0x00
53 tax
54 pla
55 skip:
56 rts
57
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