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The new method needs about 30 % less time for prime256k1 and is about twice as fast for other moduli. The base algorithm is the same. The code is also a bit smaller and doesn't need the 8 kb precomputed table. Important canges: 1. even/odd distinction so that we need to test only one of the numbers for being even. This also leads to less duplicated code. 2. Allow for shifting by 32 bits at a time in the even test. 3. Pack u,s and v,r into the same array, which saves a bit of stack memory. 4. Don't divide by two after subtraction; this simplifies code. 5. Abort as soon as u,v are equal, instead of subtracting them. 6. Use s instead of r after the loop; no negation needed. 7. New code that divides by 2^k fast without any precomputed values.
57 lines
1.7 KiB
C
57 lines
1.7 KiB
C
/**
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* Copyright (c) 2013-2014 Tomas Dzetkulic
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* Copyright (c) 2013-2014 Pavol Rusnak
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*
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* Permission is hereby granted, free of charge, to any person obtaining
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* a copy of this software and associated documentation files (the "Software"),
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* to deal in the Software without restriction, including without limitation
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* the rights to use, copy, modify, merge, publish, distribute, sublicense,
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* and/or sell copies of the Software, and to permit persons to whom the
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* Software is furnished to do so, subject to the following conditions:
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*
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* The above copyright notice and this permission notice shall be included
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* in all copies or substantial portions of the Software.
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*
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* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
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* OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
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* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
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* THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES
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* OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE,
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* ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
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* OTHER DEALINGS IN THE SOFTWARE.
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*/
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#ifndef __SECP256K1_H__
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#define __SECP256K1_H__
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#include <stdint.h>
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#include "bignum.h"
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// curve point x and y
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typedef struct {
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bignum256 x, y;
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} curve_point;
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// secp256k1 prime
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extern const bignum256 prime256k1;
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// secp256k1 initial curve point
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extern const curve_point G256k1;
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// secp256k1 order of G
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extern const bignum256 order256k1;
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// secp256k1 order of G / 2
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extern const bignum256 order256k1_half;
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// 3/2 in G_p
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extern const bignum256 three_over_two256k1;
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#if USE_PRECOMPUTED_CP
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extern const curve_point secp256k1_cp[256];
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extern const curve_point secp256k1_cp2[255];
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#endif
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#endif
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