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C arm/ecc-secp256r1-redc.asm
ifelse(<
Copyright (C) 2013 Niels Möller
This file is part of GNU Nettle.
GNU Nettle is free software: you can redistribute it and/or
modify it under the terms of either:
* the GNU Lesser General Public License as published by the Free
Software Foundation; either version 3 of the License, or (at your
option) any later version.
or
* the GNU General Public License as published by the Free
Software Foundation; either version 2 of the License, or (at your
option) any later version.
or both in parallel, as here.
GNU Nettle is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
General Public License for more details.
You should have received copies of the GNU General Public License and
the GNU Lesser General Public License along with this program. If
not, see http://www.gnu.org/licenses/.
>)
.file "ecc-secp256r1-redc.asm"
.arm
define(<RP>, <r1>)
define(<T0>, <r0>) C Overlaps unused modulo 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_modulo *m, 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)
|
