ecc-256-redc.asm 3.36 KB
Newer Older
Niels Möller's avatar
Niels Möller committed
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
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
C nettle, low-level cryptographics library
C
C Copyright (C) 2013, Niels Möller
C
C The nettle library is free software; you can redistribute it and/or modify
C it under the terms of the GNU Lesser General Public License as published by
C the Free Software Foundation; either version 2.1 of the License, or (at your
C option) any later version.
C
C The nettle library is distributed in the hope that it will be useful, but
C WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
C or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Lesser General Public
C License for more details.
C
C You should have received a copy of the GNU Lesser General Public License
C along with the nettle library; see the file COPYING.LIB.  If not, write to
C the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston,
C MA 02111-1301, USA.

	.file "ecc-256-redc.asm"
	.arm

define(<RP>, <r1>)

define(<T0>, <r0>) C Overlaps unused ecc argument
define(<T1>, <r2>)
define(<T2>, <r3>)
define(<T3>, <r4>)
define(<T4>, <r5>)
define(<T5>, <r6>)
define(<T6>, <r7>)
define(<T7>, <r8>)
define(<F0>, <r10>)
define(<F1>, <r11>)
define(<F2>, <r12>)
define(<F3>, <lr>)

	C ecc_256_redc (const struct ecc_curve *ecc, mp_limb_t *rp)
	.text
	.align 2

PROLOGUE(nettle_ecc_256_redc)
	push	{r4,r5,r6,r7,r8,r10,r11,lr}

	ldm	RP!, {T0,T1,T2,T3,T4,T5,T6,T7}

	C Set <F3,F2,F1> to the high 4 limbs of (B^2-B+1)<T2,T1,T0>
	C         T2 T1
	C   T2 T1 T0
	C   -  T2 T1 T0
	C -------------
	C   F3 F2 F1 F0


	adds	F1, T0, T2
	adcs	F2, T1, #0
	adc	F3, T2, #0

	subs	F0, T1, T0
	sbcs	F1, F1, T1	C Could also be rsc ?
	sbcs	F2, F2, T2
	sbc	F3, F3, #0

	C Add:
	C   T10 T9 T8 T7 T6 T5 T4 T3
	C +  F3 F2 F1 F0 T0 T2 T1 T0
	C --------------------------
	C    T7 T6 T5 T4 T3 T2 T1 T0

	adds	T3, T3, T0
	adcs	T1, T4, T1
	adcs	T2, T5, T2
	adcs	T6, T6, T0
	mov	T0, T3		C FIXME: Be more clever?
	mov	T3, T6
	adcs	T4, T7, F0

	ldm	RP!, {T5,T6,T7}
	adcs	T5, T5, F1
	adcs	T6, T6, F2
	adcs	T7, T7, F3

	C New F3, F2, F1, F0, also adding in carry
	adcs	F1, T0, T2
	adcs	F2, T1, #0
	adc	F3, T2, #0

	subs	F0, T1, T0
	sbcs	F1, F1, T1	C Could also be rsc ?
	sbcs	F2, F2, T2
	sbc	F3, F3, #0

	C Start adding
	adds	T3, T3, T0
	adcs	T1, T4, T1
	adcs	T2, T5, T2
	adcs	T6, T6, T0
	mov	T0, T3		C FIXME: Be more clever?
	mov	T3, T6
	adcs	T4, T7, F0

	ldm	RP!, {T5,T6,T7}
	adcs	T5, T5, F1
	adcs	T6, T6, F2
	adcs	T7, T7, F3

	C Final iteration, eliminate only T0, T1
	C Set <F2, F1, F0> to the high 3 limbs of (B^2-B+1)<T1,T0>

	C      T1 T0 T1
	C      -  T1 T0
	C -------------
	C      F2 F1 F0

	C First add in carry
	adcs	F1, T0, #0
	adcs	F2, T1, #0
	subs	F0, T1, T0
	sbcs	F1, F1, T1
	sbc	F2, F2, #0

	C Add:
	C    T9 T8 T7 T6 T5 T4 T3 T2
	C +  F2 F1 F0 T0  0 T1 T0  0
	C --------------------------
	C    F2 F1 T7 T6 T5 T4 T3 T2

	adds	T3, T3, T0
	adcs	T4, T4, T1
	adcs	T5, T5, #0
	adcs	T6, T6, T0
	adcs	T7, T7, F0
	ldm	RP!, {T0, T1}
	mov	F3, #0
	adcs	F1, F1, T0
	adcs	F2, F2, T1

	C Sum is < B^8 + p, so it's enough to fold carry once,
	C If carry, add in
	C   B^7 - B^6 - B^3 + 1  = <0, B-2, B-1, B-1, B-1, 0, 0, 1>

	C Mask from carry flag, leaving carry intact
	adc	F3, F3, #0
	rsb	F3, F3, #0

	adcs	T0, T2, #0
	adcs	T1, T3, #0
	adcs	T2, T4, #0
	adcs	T3, T5, F3
	adcs	T4, T6, F3
	adcs	T5, T7, F3
	and	F3, F3, #-2
	adcs	T6, F1, F3
	adcs	T7, F2, #0

	sub	RP, RP, #64
	stm	RP, {T0,T1,T2,T3,T4,T5,T6,T7}

	pop	{r4,r5,r6,r7,r8,r10,r11,pc}
EPILOGUE(nettle_ecc_256_redc)