gbdk-2020 | GameBoy Development Kit |
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gbdk-lib/libc/asm/mos6502/_divuint.s
1 ;-------------------------------------------------------------------------
2 ; _divuint.s - routine for division of 16 bit unsigned int
3 ;
4 ; Copyright (C) 1998, Ullrich von Bassewitz
5 ; Copyright (C) 2022, 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 _divuint
31
32 ;--------------------------------------------------------
33 ; exported symbols
34 ;--------------------------------------------------------
35 .globl __divuint_PARM_2
36 .globl __divsint_PARM_2
37 .globl __moduint_PARM_2
38 .globl __modsint_PARM_2
39 .globl __divuint
40 .globl ___udivmod16
41
42 ;--------------------------------------------------------
43 ; overlayable function parameters in zero page
44 ;--------------------------------------------------------
45 .area OSEG (PAG, OVR)
46 __divuint_PARM_2:
47 __divsint_PARM_2:
48 __moduint_PARM_2:
49 __modsint_PARM_2:
50 .ds 2
51
52 ;--------------------------------------------------------
53 ; local aliases
54 ;--------------------------------------------------------
55 .define res "___SDCC_m6502_ret0"
56 .define den "__divuint_PARM_2"
57 .define rem "___SDCC_m6502_ret2"
58 .define s1 "___SDCC_m6502_ret4"
59 .define s2 "___SDCC_m6502_ret5"
60
61 ;--------------------------------------------------------
62 ; code
63 ;--------------------------------------------------------
64 .area _CODE
65
66 __divuint:
67 jsr ___udivmod16
68 lda *res+0
69 ldx *res+1
70 rts
71
72 ___udivmod16:
73 sta *res+0
74 stx *res+1
75
76 lda #0
77 sta *rem+1
78 ldy #16
79 ; ldx __divuint_PARM_2+1
80 ; beq div16x8
81 next_bit:
82 asl *res+0
83 rol *res+1
84 rol a
85 rol *rem+1
86
87 tax
88 cmp *den+0
89 lda *rem+1
90 sbc *den+1
91 bcc L1
92 sta *rem+1
93 txa
94 sbc *den+0
95 tax
96 inc *res+0
97 L1:
98 txa
99 dey
100 bne next_bit
101 sta *rem+0
102 rts
103
104 ;div16x8:
105 ;LL0:
106 ; asl *___SDCC_m6502_ret0+0
107 ; rol *___SDCC_m6502_ret0+1
108 ; rol a
109 ; bcs LL1
110 ; cmp __divuint_PARM_2+0
111 ; bcc LL2
112 ;LL1:
113 ; sbc __divuint_PARM_2+0
114 ; inc *___SDCC_m6502_ret0+0
115 ;LL2:
116 ; dey
117 ; bne LL0
118 ; sta *___SDCC_m6502_ret2+0
119 ;
120 ; lda *___SDCC_m6502_ret0+0
121 ; ldx *___SDCC_m6502_ret0+1
122 ; rts
123
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