ecc-521-modp.asm

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-521-modp.asm"
	.arm

define(<HP>, <r0>)
define(<RP>, <r1>)
define(<T0>, <r2>)
define(<T1>, <r3>)
define(<T2>, <r4>)
define(<F0>, <r5>)
define(<F1>, <r6>)
define(<F2>, <r7>)
define(<F3>, <r8>)
define(<H>, <r12>)
define(<N>, <lr>)

	C ecc_521_modp (const struct ecc_curve *ecc, mp_limb_t *rp)
	.text
.Lc511:
	.int 511

	.align 2

PROLOGUE(nettle_ecc_521_modp)
	push	{r4,r5,r6,r7,r8,lr}

	C Use that B^17 = 2^23 (mod p)
	ldr	F3, [RP, #+68]		C 17
	add	HP, RP, #72		C 18
	ldr	T0, [RP]		C 0
	adds	T0, T0, F3, lsl	#23
	str	T0, [RP], #+4
	mov	N, #5

	C 5 iterations, reading limbs 18-20, 21-23, 24-26, 27-29, 30-32
	C and adding to limbs          1-3,    4-6,   7-9, 19-12, 13-15
.Loop:
	ldm	RP, {T0,T1,T2}		C  1+3*k --  3+3*k
	lsr	F0, F3, #9
	ldm	HP!, {F1,F2,F3}		C 18+3*k -- 20+3*k
	orr	F0, F0, F1, lsl #23
	lsr	F1, F1, #9
	orr	F1, F1, F2, lsl #23
	lsr	F2, F2, #9
	orr	F2, F2, F3, lsl #23
	adcs	T0, T0, F0
	adcs	T1, T1, F1
	adcs	T2, T2, F2
	sub	N, N, #1
	stm	RP!,{T0,T1,T2}
	teq	N, #0
	bne	.Loop

	ldr	F0, [RP], #-64		C 16
	ldr	F1, [HP]		C 33
	ldr	T0, .Lc511

	C Handling of high limbs
	C F0 = rp[16] + carry in + F3 >> 9
	adcs	F0, F0, F3, lsr #9
	C Copy low 9 bits to H, then shift right including carry
	and	H, F0, T0
	rrx	F0, F0
	lsr	F0, F0, #8
	C Add in F1 = rp[33], with weight 2^1056 = 2^14
	adds	F0, F0, F1, lsl #14
	lsr	F1, F1, #18
	adc	F1, F1, #0

	ldm	RP, {T0, T1}		C 0-1
	adds	T0, T0, F0
	adcs	T1, T1, F1
	stm	RP!, {T0, T1}

	ldm	RP, {T0,T1,T2,F0,F1,F2,F3}	C 2-8
	adcs	T0, T0, #0
	adcs	T1, T1, #0
	adcs	T2, T2, #0
	adcs	F0, F0, #0
	adcs	F1, F1, #0
	adcs	F2, F2, #0
	adcs	F3, F3, #0
	stm	RP!, {T0,T1,T2,F0,F1,F2,F3}	C 2-8
	ldm	RP, {T0,T1,T2,F0,F1,F2,F3}	C 9-15
	adcs	T0, T0, #0
	adcs	T1, T1, #0
	adcs	T2, T2, #0
	adcs	F0, F0, #0
	adcs	F1, F1, #0
	adcs	F2, F2, #0
	adcs	F3, F3, #0
	adcs	H, H, #0
	stm	RP, {T0,T1,T2,F0,F1,F2,F3,H}	C 9-16

	pop	{r4,r5,r6,r7,r8,pc}
EPILOGUE(nettle_ecc_521_modp)