Montgomery multiplication for ARMv4.

crypto/bn/asm/armv4t-mont.pl

+#!/usr/bin/env perl
+
+# ====================================================================
+# Written by Andy Polyakov <appro@fy.chalmers.se> for the OpenSSL
+# project. The module is, however, dual licensed under OpenSSL and
+# CRYPTOGAMS licenses depending on where you obtain it. For further
+# details see http://www.openssl.org/~appro/cryptogams/.
+# ====================================================================
+
+# January 2007.
+
+# Montgomery multiplication for ARMv4.
+#
+# Performance improvement naturally varies among CPU implementations
+# and compilers. The code was observed to provide +65-35% improvement
+# [depending on key length, less for longer keys] on ARM920T, and
+# +115-80% on Intel IXP425. This is compared to pre-bn_mul_mont code
+# base and compiler generated code with in-lined umull and even umlal
+# instructions. The latter means that this code didn't really have an 
+# "advantage" of utilizing some "secret" instruction.
+#
+# The code is interoperable with Thumb ISA and is rather compact, less
+# than 1/2KB. Windows CE port would be trivial, as it's exclusively
+# about decorations, ABI and instruction syntax are identical.
+
+$num="r0";	# starts as num argument, but holds &tp[num-1]
+$ap="r1";
+$bp="r2"; $bi="r2"; $rp="r2";
+$np="r3";
+$tp="r4";
+$aj="r5";
+$nj="r6";
+$tj="r7";
+$n0="r8";
+###########	# r9 is reserved by ELF as platform specific, e.g. TLS pointer
+$alo="r10";	# sl, gcc uses it to keep @GOT
+$ahi="r11";	# fp
+$nlo="r12";	# ip
+###########	# r13 is stack pointer
+$nhi="r14";	# lr
+###########	# r15 is program counter
+
+#### argument block layout relative to &tp[num-1], a.k.a. $num
+$_rp="$num,#12*4";
+# ap permanently resides in r1
+$_bp="$num,#13*4";
+# np permanently resides in r3
+$_n0="$num,#14*4";
+$_num="$num,#15*4";	$_bpend=$_num;
+
+$code=<<___;
+.text
+
+.global	bn_mul_mont
+.type	bn_mul_mont,%function
+
+.align	2
+bn_mul_mont:
+	stmdb	sp!,{r0,r2}		@ sp points at argument block
+	ldr	$num,[sp,#3*4]		@ load num
+	cmp	$num,#2
+	movlt	r0,#0
+	addlt	sp,sp,#2*4
+	bxlt	lr			@ interoperate with Thumb ISA
+
+	stmdb	sp!,{r4-r12,lr}		@ save 10 registers
+
+	mov	$num,$num,lsl#2		@ rescale $num for byte count
+	sub	sp,sp,$num		@ alloca(4*num)
+	sub	sp,sp,#4		@ +extra dword
+	sub	$num,$num,#4		@ "num=num-1"
+	add	$tp,$bp,$num		@ &bp[num-1]
+
+	add	$num,sp,$num		@ $num to point at &tp[num-1]
+	ldr	$n0,[$_n0]		@ &n0
+	ldr	$bi,[$bp]		@ bp[0]
+	ldr	$aj,[$ap],#4		@ ap[0],ap++
+	ldr	$nj,[$np],#4		@ np[0],np++
+	ldr	$n0,[$n0]		@ *n0
+	str	$tp,[$_bpend]		@ save &bp[num]
+
+	umull	$alo,$ahi,$aj,$bi	@ ap[0]*bp[0]
+	str	$n0,[$_n0]		@ save n0 value
+	mul	$n0,$alo,$n0		@ "tp[0]"*n0
+	mov	$nlo,#0
+	umlal	$alo,$nlo,$nj,$n0	@ np[0]*n0+"t[0]"
+	mov	$tp,sp
+
+.L1st:
+	ldr	$aj,[$ap],#4		@ ap[j],ap++
+	mov	$alo,$ahi
+	mov	$ahi,#0
+	umlal	$alo,$ahi,$aj,$bi	@ ap[j]*bp[0]
+	ldr	$nj,[$np],#4		@ np[j],np++
+	mov	$nhi,#0
+	umlal	$nlo,$nhi,$nj,$n0	@ np[j]*n0
+	adds	$nlo,$nlo,$alo
+	str	$nlo,[$tp],#4		@ tp[j-1]=,tp++
+	adc	$nlo,$nhi,#0
+	cmp	$tp,$num
+	bne	.L1st
+
+	adds	$nlo,$nlo,$ahi
+	mov	$nhi,#0
+	adc	$nhi,$nhi,#0
+	ldr	$tp,[$_bp]		@ restore bp
+	str	$nlo,[$num]		@ tp[num-1]=
+	ldr	$n0,[$_n0]		@ restore n0
+	str	$nhi,[$num,#4]		@ tp[num]=
+
+.Louter:
+	sub	$tj,$num,sp		@ "original" $num-1 value
+	sub	$ap,$ap,$tj		@ "rewind" ap to &ap[1]
+	sub	$np,$np,$tj		@ "rewind" np to &np[1]
+	ldr	$bi,[$tp,#4]!		@ *(++bp)
+	ldr	$aj,[$ap,#-4]		@ ap[0]
+	ldr	$nj,[$np,#-4]		@ np[0]
+	ldr	$alo,[sp]		@ tp[0]
+	ldr	$tj,[sp,#4]		@ tp[1]
+
+	mov	$ahi,#0
+	umlal	$alo,$ahi,$aj,$bi	@ ap[0]*bp[i]+tp[0]
+	str	$tp,[$_bp]		@ save bp
+	mul	$n0,$alo,$n0
+	mov	$nlo,#0
+	umlal	$alo,$nlo,$nj,$n0	@ np[0]*n0+"tp[0]"
+	mov	$tp,sp
+
+.Linner:
+	ldr	$aj,[$ap],#4		@ ap[j],ap++
+	adds	$alo,$ahi,$tj		@ +=tp[j]
+	mov	$ahi,#0
+	umlal	$alo,$ahi,$aj,$bi	@ ap[j]*bp[i]
+	ldr	$nj,[$np],#4		@ np[j],np++
+	mov	$nhi,#0
+	umlal	$nlo,$nhi,$nj,$n0	@ np[j]*n0
+	ldr	$tj,[$tp,#8]		@ tp[j+1]
+	adc	$ahi,$ahi,#0
+	adds	$nlo,$nlo,$alo
+	str	$nlo,[$tp],#4		@ tp[j-1]=,tp++
+	adc	$nlo,$nhi,#0
+	cmp	$tp,$num
+	bne	.Linner
+
+	adds	$nlo,$nlo,$ahi
+	mov	$nhi,#0
+	adc	$nhi,$nhi,#0
+	adds	$nlo,$nlo,$tj
+	adc	$nhi,$nhi,#0
+	ldr	$tp,[$_bp]		@ restore bp
+	ldr	$tj,[$_bpend]		@ restore &bp[num]
+	str	$nlo,[$num]		@ tp[num-1]=
+	ldr	$n0,[$_n0]		@ restore n0
+	str	$nhi,[$num,#4]		@ tp[num]=
+
+	cmp	$tp,$tj
+	bne	.Louter
+
+	ldr	$rp,[$_rp]		@ pull rp
+	add	$num,$num,#4		@ $num to point at &tp[num]
+	sub	$aj,$num,sp		@ "original" num value
+	mov	$tp,sp			@ "rewind" $tp
+	sub	$np,$np,$aj		@ "rewind" $np to &np[0]
+
+	cmp	$nhi,#0			@ upmost carry
+	bne	.Lsub
+	cmp	$nlo,$nj		@ tp[num-1]-np[num-1]
+	bhs	.Lsub
+
+.Lcopy:	ldr	$tj,[$tp]
+	str	sp,[$tp],#4		@ zap tp
+	str	$tj,[$rp],#4
+	cmp	$tp,$num
+	bne	.Lcopy
+
+.Lexit:	add	sp,$num,#4		@ skip over tp[num+1]
+	ldmia	sp!,{r4-r12,lr}		@ restore registers
+	add	sp,sp,#2*4		@ skip over {r0,r2}
+	mov	r0,#1
+	bx	lr			@ interoperate with Thumb ISA
+
+.Lsub:	ldr	$tj,[$tp],#4
+	ldr	$nj,[$np],#4
+	sbcs	$tj,$tj,$nj		@ tp[j]-np[j]
+	str	$tj,[$rp],#4		@ rp[j]=
+	teq	$tp,$num		@ preserve carry
+	bne	.Lsub
+	sbcs	$nhi,$nhi,#0		@ upmost carry
+	mov	$tp,sp			@ "rewind" $tp
+	sub	$rp,$rp,$aj		@ "rewind" $rp
+	blo	.Lcopy			@ tp was less after all
+
+.Lzap:	str	sp,[$tp],#4
+	cmp	$tp,$num
+	bne	.Lzap
+	bal	.Lexit
+.size	bn_mul_mont,.-bn_mul_mont
+.asciz	"Montgomery multiplication for ARMv4, CRYPTOGAMS by <appro\@openssl.org>"
+___
+
+print $code;
+close STDOUT;