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C nettle, low-level cryptographics library
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C Copyright (C) 2013, Niels Möller
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C The nettle library is free software; you can redistribute it and/or modify
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C it under the terms of the GNU Lesser General Public License as published by
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C the Free Software Foundation; either version 2.1 of the License, or (at your
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C option) any later version.
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C The nettle library is distributed in the hope that it will be useful, but
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C WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
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C or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public
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C License for more details.
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C You should have received a copy of the GNU Lesser General Public License
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C along with the nettle library; see the file COPYING.LIB. If not, write to
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C the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston,
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.file "ecc-384-modp.asm"
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C ecc_384_modp (const struct ecc_curve *ecc, mp_limb_t *rp)
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PROLOGUE(nettle_ecc_384_modp)
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push {r4,r5,r6,r7,r8,r10,lr}
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ldm RP, {T0, T1, T2, T3} C 20-23
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C First get top 4 limbs, which need folding twice, as
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C F2 F1 F0 Always fits
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ldm RP, {T0, T1, T2, T3} C 12-15
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adcs F4, F4, #0 C Do F4 later
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C Add to low part, keeping carry (positive or negative) in H
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ldm RP, {T0, T1, T2, T3} C 0-3
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stm RP!, {T0,T1,T2,T3} C 0-3
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ldm RP, {T0,T1,T2,T3} C 4-7
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C First, propagate carry
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asr H, #31 C Sign extend
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ldr F0, [RP, #+48] C 16
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ldr F1, [RP, #+52] C 17-18
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ldr F3, [RP, #+60] C 19
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stm RP!, {T0,T1,T2,T3}
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C Fold high limbs, we need to add in
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C F4 F4 0 -F4 F4 H H 0 -H H
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C We always have F4 >= 0, but we can have H < 0.
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C Sign extension gets tricky when F4 = 0 and H < 0.
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ldm RP, {T0,T1,T2,T3} C 0-3
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C Define S = H >> 31 (asr), we then have
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C And we get underflow in S - H iff H > 0
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subs F1, H, F0 C 0,C=1 -H,C=0 0,C=1
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sbc F2, F2, F2 C 0 -1 0
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sbc F3, F0, #0 C 0 H-1 -1
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adc H, H, F0 C 0+cy H+cy -2+cy
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stm RP!, {T0,T1,T2,T3} C 0-3
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ldm RP, {T0,T1,T2,T3} C 4-7
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stm RP!, {T0,T1,T2,T3} C 4-7
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ldm RP, {T0,T1,T2,T3} C 8-11
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stm RP, {T0,T1,T2,T3} C 8-11
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C Final (unlikely) carry
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ldm RP, {T0,T1,T2,T3} C 0-3
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stm RP!, {T0,T1,T2,T3} C 0-3
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ldm RP, {T0,T1,T2,T3} C 4-7
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stm RP!, {T0,T1,T2,T3} C 4-7
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ldm RP, {T0,T1,T2,T3} C 8-11
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stm RP!, {T0,T1,T2,T3} C 8-11
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pop {r4,r5,r6,r7,r8,r10,pc}
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EPILOGUE(nettle_ecc_384_modp)