gbdk-2020 | GameBoy Development Kit |
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gbdk-lib/libc/asm/mos6502/_mulschar.s
1 ;-------------------------------------------------------------------------
2 ; _mulschar.s - routine for multiplication of 8 bit signed char
3 ;
4 ; Copyright (C) 2009, Ullrich von Bassewitz
5 ; Copyright (C) 2022-2023, 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 _mulschar
31
32 ;--------------------------------------------------------
33 ; exported symbols
34 ;--------------------------------------------------------
35 .globl __mulschar
36 .globl __muluschar
37 .globl __mulsuchar
38
39 ;--------------------------------------------------------
40 ; overlayable function parameters in zero page
41 ;--------------------------------------------------------
42 .area OSEG (PAG, OVR)
43
44 ;--------------------------------------------------------
45 ; local aliases
46 ;--------------------------------------------------------
47 .define arg1 "___SDCC_m6502_ret0"
48 .define arg2 "___SDCC_m6502_ret2"
49 .define s1 "___SDCC_m6502_ret4"
50 .define s2 "___SDCC_m6502_ret5"
51
52 ;--------------------------------------------------------
53 ; code
54 ;--------------------------------------------------------
55 .area _CODE
56
57 __mulschar:
58 sta *s1
59 cmp #0x00
60 bpl pos1
61 sec
62 eor #0xff
63 adc #0x00
64 pos1:
65 sta *arg1
66 txa
67 sta *s2
68 bpl pos2
69 sec
70 eor #0xff
71 adc #0x00
72 pos2:
73 sta *arg2
74
75 jsr ___umul8
76 lda *s1
77 eor *s2
78 bpl skip
79 lda arg2
80 jmp ___negax
81
82 skip: lda arg2
83 rts
84
85 __muluschar:
86 stx *__mulint_PARM_2
87 ldx #0x00
88 stx *__mulint_PARM_2+1
89 cmp #0x00
90 bpl pos1m
91 ldx #0xff
92 pos1m:
93 jmp __mulint
94
95 __mulsuchar:
96 sta *__mulint_PARM_2
97 txa
98 ldx #0x00
99 stx *__mulint_PARM_2+1
100 cmp #0x00
101 bpl pos2m
102 ldx #0xff
103 pos2m:
104 jmp __mulint
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