gbdk-2020 | GameBoy Development Kit |
| download: https://git.y1.nz/archives/gbdk.tar.gz | |
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gbdk-lib/libc/asm/sm83/memcpy.s
1 ;--------------------------------------------------------------------------
2 ; memcpy.s
3 ;
4 ; Copies in groups of four. Algorithm is Duff's device.
5 ;
6 ; Copyright (c) 2021, Philipp Klaus Krause
7 ; Copyright (c) 2022, Sebastian 'basxto' Riedel <sdcc@basxto.de>
8 ;
9 ; This library is free software; you can redistribute it and/or modify it
10 ; under the terms of the GNU General Public License as published by the
11 ; Free Software Foundation; either version 2, or (at your option) any
12 ; later version.
13 ;
14 ; This library is distributed in the hope that it will be useful,
15 ; but WITHOUT ANY WARRANTY; without even the implied warranty of
16 ; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
17 ; GNU General Public License for more details.
18 ;
19 ; You should have received a copy of the GNU General Public License
20 ; along with this library; see the file COPYING. If not, write to the
21 ; Free Software Foundation, 51 Franklin Street, Fifth Floor, Boston,
22 ; MA 02110-1301, USA.
23 ;
24 ; As a special exception, if you link this library with other files,
25 ; some of which are compiled with SDCC, to produce an executable,
26 ; this library does not by itself cause the resulting executable to
27 ; be covered by the GNU General Public License. This exception does
28 ; not however invalidate any other reasons why the executable file
29 ; might be covered by the GNU General Public License.
30 ;--------------------------------------------------------------------------
31
32 .area _CODE
33
34 .globl _memcpy
35 .globl ___memcpy
36
37 ; gets called by memmove for (s >= d)
38 ; bigger than the old algorithm but faster for n>=5
39 _memcpy::
40 ___memcpy::
41 ;dest in de
42 ;src in bc
43 ;n in sp+2,sp+3
44 push de
45 ldhl sp, #5
46 ld a, (hl-)
47 ld l, (hl)
48 ld h, b
49 ld b, a
50 ld a, l
51 ld l, c
52 srl b
53 rra
54 ld c, a
55 ;dest in de (backup in sp+0,sp+1)
56 ;src in hl
57 ;n/2 in bc
58 ;LSB of bc in carry
59 jr nc, skip_one
60 ld a, (hl+)
61 ld (de), a
62 inc de
63 skip_one:
64 ;n/2 in bc
65 ;shift second LSB to carry
66 srl b
67 rr c
68 ;n/4 in bc
69 inc b
70 inc c
71 jr nc, test
72 jr copy_two
73 .irp idx,copy_four,copy_two
74 idx:
75 .rept 2
76 ld a, (hl+)
77 ld (de), a
78 inc de
79 .endm
80 .endm
81 test:
82 .irp idx,c,b
83 dec idx
84 jr nz, copy_four
85 .endm
86
87 end:
88 ;restore dest
89 pop bc
90 ;get return address
91 pop hl
92 ;throw away n
93 pop af
94 jp (hl)
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