1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
|
dnl PowerPC-32 mpn_divexact_by3 -- mpn by 3 exact division
dnl Copyright 2002, 2003, 2005, 2006 Free Software Foundation, Inc.
dnl This file is part of the GNU MP Library.
dnl
dnl The GNU MP Library is free software; you can redistribute it and/or modify
dnl it under the terms of either:
dnl
dnl * the GNU Lesser General Public License as published by the Free
dnl Software Foundation; either version 3 of the License, or (at your
dnl option) any later version.
dnl
dnl or
dnl
dnl * the GNU General Public License as published by the Free Software
dnl Foundation; either version 2 of the License, or (at your option) any
dnl later version.
dnl
dnl or both in parallel, as here.
dnl
dnl The GNU MP Library is distributed in the hope that it will be useful, but
dnl WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
dnl or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
dnl for more details.
dnl
dnl You should have received copies of the GNU General Public License and the
dnl GNU Lesser General Public License along with the GNU MP Library. If not,
dnl see https://www.gnu.org/licenses/.
include(`../config.m4')
C cycles/limb
C 603e: ?
C 604e: 5
C 75x (G3): ?
C 7400,7410 (G4): 8
C 744x,745x (G4+): 6
C power4/ppc970: 12
C power5: ?
C void mpn_divexact_by3 (mp_ptr dst, mp_srcptr src, mp_size_t size);
C
C We avoid the slow subfe instruction and instead rely on an extremely unlikely
C branch.
C
C The mullw has the inverse in the first operand, since 0xAA..AB won't allow
C any early-out. The src[] data normally won't either, but there's at least
C a chance, whereas 0xAA..AB never will. If, for instance, src[] is all
C zeros (not a sensible input of course) we run at 7.0 c/l on ppc750.
C
C The mulhwu has the "3" multiplier in the second operand, which lets 750 and
C 7400 use an early-out.
C INPUT PARAMETERS
define(`rp', `r3')
define(`up', `r4')
define(`n', `r5')
define(`cy', `r6')
ASM_START()
PROLOGUE(mpn_divexact_by3c)
lwz r11, 0(up)
mtctr n
lis r12, 0xAAAA
ori r12, r12, 0xAAAB
li r10, 3
cmplw cr7, cy, r11
subf r11, cy, r11
mullw r0, r11, r12
stw r0, 0(rp)
bdz L(one)
L(top): lwzu r9, 4(up)
mulhwu r7, r0, r10
bgt- cr7, L(adj) C very unlikely branch
L(bko): cmplw cr7, r7, r9
subf r0, r7, r9
mullw r0, r12, r0
stwu r0, 4(rp)
bdnz L(top)
L(one): mulhwu r3, r0, r10
blelr+ cr7
addi r3, r3, 1
blr
L(adj): addi r7, r7, 1
b L(bko)
EPILOGUE()
ASM_END()
|
