gbdk-2020 | GameBoy Development Kit |
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gbdk-lib/libc/asm/z80/divsigned.s
1 ;--------------------------------------------------------------------------
2 ; divsigned.s
3 ;
4 ; Copyright (C) 2000-2021, Michael Hope, Philipp Klaus Krause
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 __divsint
32 .globl __divschar
33
34 __divschar:
35 ld e, l
36 ld l, a
37
38 __div8::
39 ld a, l ; Sign extend
40 rlca
41 sbc a,a
42 ld h, a
43 __div_signexte::
44 ld a, e ; Sign extend
45 rlca
46 sbc a, a
47 ld d, a
48 ; Fall through to __div16
49
50 ;; signed 16-bit division
51 ;;
52 ;; Entry conditions
53 ;; HL = dividend
54 ;; DE = divisor
55 ;;
56 ;; Exit conditions
57 ;; DE = quotient
58 ;; HL = remainder
59 ;;
60 ;; Register used: AF,B,DE,HL
61 __divsint:
62 __div16::
63 ;; Determine sign of quotient by xor-ing high bytes of dividend
64 ;; and divisor. Quotient is positive if signs are the same, negative
65 ;; if signs are different
66 ;; Remainder has same sign as dividend
67 ld a, h ; Get high byte of dividend
68 xor a, d ; Xor with high byte of divisor
69 rla ; Sign of quotient goes into the carry
70 ld a, h ; Get high byte of dividend
71 push af ; Save sign of both quotient and reminder
72
73 ; Take absolute value of dividend
74 rla
75 jr NC, .chkde ; Jump if dividend is positive
76 sub a, a ; Substract dividend from 0
77 sub a, l
78 ld l, a
79 sbc a, a ; Propagate borrow (A=0xFF if borrow)
80 sub a, h
81 ld h, a
82
83 ; Take absolute value of divisor
84 .chkde:
85 bit 7, d
86 jr Z, .dodiv ; Jump if divisor is positive
87 sub a, a ; Subtract divisor from 0
88 sub a, e
89 ld e, a
90 sbc a, a ; Propagate borrow (A=0xFF if borrow)
91 sub a, d
92 ld d, a
93
94 ; Divide absolute values
95 .dodiv:
96 call __divu16
97
98 .fix_quotient:
99 ; Negate quotient if it is negative
100 pop af ; recover sign of quotient
101 ret NC ; Jump if quotient is positive
102 ld b, a
103 sub a, a ; Subtract quotient from 0
104 sub a, e
105 ld e, a
106 sbc a, a ; Propagate borrow (A=0xFF if borrow)
107 sub a, d
108 ld d, a
109 ld a, b
110 ret
111
112 __get_remainder::
113 ; Negate remainder if it is negative.
114 rla
115 ex de, hl
116 ret NC ; Return if remainder is positive
117 sub a, a ; Subtract quotient from 0
118 sub a, e
119 ld e, a
120 sbc a, a ; Propagate borrow (A=0xFF if borrow)
121 sub a, d
122 ld d, a
123 ret
124
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