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make SECP256K1_SCALAR_CONST reduce modulo exhaustive group order

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Pieter Wuille 2022-12-30 12:13:46 -05:00
parent 2140da9cd5
commit ba523be067
1 changed files with 9 additions and 2 deletions
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11
src/scalar_low.h
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@ -1,5 +1,5 @@
/***********************************************************************
* Copyright (c) 2015 Andrew Poelstra *
* Copyright (c) 2015, 2022 Andrew Poelstra, Pieter Wuille *
* Distributed under the MIT software license, see the accompanying *
* file COPYING or https://www.opensource.org/licenses/mit-license.php.*
***********************************************************************/
@ -12,6 +12,13 @@
/** A scalar modulo the group order of the secp256k1 curve. */
typedef uint32_t secp256k1_scalar;
#define SECP256K1_SCALAR_CONST(d7, d6, d5, d4, d3, d2, d1, d0) (d0)
/* A compile-time constant equal to 2^32 (modulo order). */
#define SCALAR_2P32 ((0xffffffffUL % EXHAUSTIVE_TEST_ORDER) + 1U)
/* Compute a*2^32 + b (modulo order). */
#define SCALAR_HORNER(a, b) (((uint64_t)(a) * SCALAR_2P32 + (b)) % EXHAUSTIVE_TEST_ORDER)
/* Evaluates to the provided 256-bit constant reduced modulo order. */
#define SECP256K1_SCALAR_CONST(d7, d6, d5, d4, d3, d2, d1, d0) SCALAR_HORNER(SCALAR_HORNER(SCALAR_HORNER(SCALAR_HORNER(SCALAR_HORNER(SCALAR_HORNER(SCALAR_HORNER((d7), (d6)), (d5)), (d4)), (d3)), (d2)), (d1)), (d0))
#endif /* SECP256K1_SCALAR_REPR_H */