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1#!/usr/bin/env perl
2
3# ====================================================================
4# Written by Andy Polyakov <appro@fy.chalmers.se> for the OpenSSL
5# project. The module is, however, dual licensed under OpenSSL and
6# CRYPTOGAMS licenses depending on where you obtain it. For further
7# details see http://www.openssl.org/~appro/cryptogams/.
8# ====================================================================
9
10# January 2007.
11
12# Montgomery multiplication for ARMv4.
13#
14# Performance improvement naturally varies among CPU implementations
15# and compilers. The code was observed to provide +65-35% improvement
16# [depending on key length, less for longer keys] on ARM920T, and
17# +115-80% on Intel IXP425. This is compared to pre-bn_mul_mont code
18# base and compiler generated code with in-lined umull and even umlal
19# instructions. The latter means that this code didn't really have an
20# "advantage" of utilizing some "secret" instruction.
21#
22# The code is interoperable with Thumb ISA and is rather compact, less
23# than 1/2KB. Windows CE port would be trivial, as it's exclusively
24# about decorations, ABI and instruction syntax are identical.
25
26$num="r0";	# starts as num argument, but holds &tp[num-1]
27$ap="r1";
28$bp="r2"; $bi="r2"; $rp="r2";
29$np="r3";
30$tp="r4";
31$aj="r5";
32$nj="r6";
33$tj="r7";
34$n0="r8";
35###########	# r9 is reserved by ELF as platform specific, e.g. TLS pointer
36$alo="r10";	# sl, gcc uses it to keep @GOT
37$ahi="r11";	# fp
38$nlo="r12";	# ip
39###########	# r13 is stack pointer
40$nhi="r14";	# lr
41###########	# r15 is program counter
42
43#### argument block layout relative to &tp[num-1], a.k.a. $num
44$_rp="$num,#12*4";
45# ap permanently resides in r1
46$_bp="$num,#13*4";
47# np permanently resides in r3
48$_n0="$num,#14*4";
49$_num="$num,#15*4";	$_bpend=$_num;
50
51$code=<<___;
52.text
53
54.global	bn_mul_mont
55.type	bn_mul_mont,%function
56
57.align	2
58bn_mul_mont:
59	stmdb	sp!,{r0,r2}		@ sp points at argument block
60	ldr	$num,[sp,#3*4]		@ load num
61	cmp	$num,#2
62	movlt	r0,#0
63	addlt	sp,sp,#2*4
64	blt	.Labrt
65
66	stmdb	sp!,{r4-r12,lr}		@ save 10 registers
67
68	mov	$num,$num,lsl#2		@ rescale $num for byte count
69	sub	sp,sp,$num		@ alloca(4*num)
70	sub	sp,sp,#4		@ +extra dword
71	sub	$num,$num,#4		@ "num=num-1"
72	add	$tp,$bp,$num		@ &bp[num-1]
73
74	add	$num,sp,$num		@ $num to point at &tp[num-1]
75	ldr	$n0,[$_n0]		@ &n0
76	ldr	$bi,[$bp]		@ bp[0]
77	ldr	$aj,[$ap],#4		@ ap[0],ap++
78	ldr	$nj,[$np],#4		@ np[0],np++
79	ldr	$n0,[$n0]		@ *n0
80	str	$tp,[$_bpend]		@ save &bp[num]
81
82	umull	$alo,$ahi,$aj,$bi	@ ap[0]*bp[0]
83	str	$n0,[$_n0]		@ save n0 value
84	mul	$n0,$alo,$n0		@ "tp[0]"*n0
85	mov	$nlo,#0
86	umlal	$alo,$nlo,$nj,$n0	@ np[0]*n0+"t[0]"
87	mov	$tp,sp
88
89.L1st:
90	ldr	$aj,[$ap],#4		@ ap[j],ap++
91	mov	$alo,$ahi
92	mov	$ahi,#0
93	umlal	$alo,$ahi,$aj,$bi	@ ap[j]*bp[0]
94	ldr	$nj,[$np],#4		@ np[j],np++
95	mov	$nhi,#0
96	umlal	$nlo,$nhi,$nj,$n0	@ np[j]*n0
97	adds	$nlo,$nlo,$alo
98	str	$nlo,[$tp],#4		@ tp[j-1]=,tp++
99	adc	$nlo,$nhi,#0
100	cmp	$tp,$num
101	bne	.L1st
102
103	adds	$nlo,$nlo,$ahi
104	mov	$nhi,#0
105	adc	$nhi,$nhi,#0
106	ldr	$tp,[$_bp]		@ restore bp
107	str	$nlo,[$num]		@ tp[num-1]=
108	ldr	$n0,[$_n0]		@ restore n0
109	str	$nhi,[$num,#4]		@ tp[num]=
110
111.Louter:
112	sub	$tj,$num,sp		@ "original" $num-1 value
113	sub	$ap,$ap,$tj		@ "rewind" ap to &ap[1]
114	sub	$np,$np,$tj		@ "rewind" np to &np[1]
115	ldr	$bi,[$tp,#4]!		@ *(++bp)
116	ldr	$aj,[$ap,#-4]		@ ap[0]
117	ldr	$nj,[$np,#-4]		@ np[0]
118	ldr	$alo,[sp]		@ tp[0]
119	ldr	$tj,[sp,#4]		@ tp[1]
120
121	mov	$ahi,#0
122	umlal	$alo,$ahi,$aj,$bi	@ ap[0]*bp[i]+tp[0]
123	str	$tp,[$_bp]		@ save bp
124	mul	$n0,$alo,$n0
125	mov	$nlo,#0
126	umlal	$alo,$nlo,$nj,$n0	@ np[0]*n0+"tp[0]"
127	mov	$tp,sp
128
129.Linner:
130	ldr	$aj,[$ap],#4		@ ap[j],ap++
131	adds	$alo,$ahi,$tj		@ +=tp[j]
132	mov	$ahi,#0
133	umlal	$alo,$ahi,$aj,$bi	@ ap[j]*bp[i]
134	ldr	$nj,[$np],#4		@ np[j],np++
135	mov	$nhi,#0
136	umlal	$nlo,$nhi,$nj,$n0	@ np[j]*n0
137	ldr	$tj,[$tp,#8]		@ tp[j+1]
138	adc	$ahi,$ahi,#0
139	adds	$nlo,$nlo,$alo
140	str	$nlo,[$tp],#4		@ tp[j-1]=,tp++
141	adc	$nlo,$nhi,#0
142	cmp	$tp,$num
143	bne	.Linner
144
145	adds	$nlo,$nlo,$ahi
146	mov	$nhi,#0
147	adc	$nhi,$nhi,#0
148	adds	$nlo,$nlo,$tj
149	adc	$nhi,$nhi,#0
150	ldr	$tp,[$_bp]		@ restore bp
151	ldr	$tj,[$_bpend]		@ restore &bp[num]
152	str	$nlo,[$num]		@ tp[num-1]=
153	ldr	$n0,[$_n0]		@ restore n0
154	str	$nhi,[$num,#4]		@ tp[num]=
155
156	cmp	$tp,$tj
157	bne	.Louter
158
159	ldr	$rp,[$_rp]		@ pull rp
160	add	$num,$num,#4		@ $num to point at &tp[num]
161	sub	$aj,$num,sp		@ "original" num value
162	mov	$tp,sp			@ "rewind" $tp
163	mov	$ap,$tp			@ "borrow" $ap
164	sub	$np,$np,$aj		@ "rewind" $np to &np[0]
165
166	subs	$tj,$tj,$tj		@ "clear" carry flag
167.Lsub:	ldr	$tj,[$tp],#4
168	ldr	$nj,[$np],#4
169	sbcs	$tj,$tj,$nj		@ tp[j]-np[j]
170	str	$tj,[$rp],#4		@ rp[j]=
171	teq	$tp,$num		@ preserve carry
172	bne	.Lsub
173	sbcs	$nhi,$nhi,#0		@ upmost carry
174	mov	$tp,sp			@ "rewind" $tp
175	sub	$rp,$rp,$aj		@ "rewind" $rp
176
177	and	$ap,$tp,$nhi
178	bic	$np,$rp,$nhi
179	orr	$ap,$ap,$np		@ ap=borrow?tp:rp
180
181.Lcopy:	ldr	$tj,[$ap],#4		@ copy or in-place refresh
182	str	sp,[$tp],#4		@ zap tp
183	str	$tj,[$rp],#4
184	cmp	$tp,$num
185	bne	.Lcopy
186
187	add	sp,$num,#4		@ skip over tp[num+1]
188	ldmia	sp!,{r4-r12,lr}		@ restore registers
189	add	sp,sp,#2*4		@ skip over {r0,r2}
190	mov	r0,#1
191.Labrt:	tst	lr,#1
192	moveq	pc,lr			@ be binary compatible with V4, yet
193	bx	lr			@ interoperable with Thumb ISA:-)
194.size	bn_mul_mont,.-bn_mul_mont
195.asciz	"Montgomery multiplication for ARMv4, CRYPTOGAMS by <appro\@openssl.org>"
196.align	2
197___
198
199$code =~ s/\bbx\s+lr\b/.word\t0xe12fff1e/gm;	# make it possible to compile with -march=armv4
200print $code;
201close STDOUT;
202