mirror of https://github.com/jb55/nostril.git
63 lines
2.3 KiB
C
63 lines
2.3 KiB
C
/***********************************************************************
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* Copyright (c) 2013, 2014 Pieter Wuille *
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* Distributed under the MIT software license, see the accompanying *
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* file COPYING or https://www.opensource.org/licenses/mit-license.php.*
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***********************************************************************/
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#ifndef SECP256K1_FIELD_REPR_H
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#define SECP256K1_FIELD_REPR_H
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#include <stdint.h>
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/** This field implementation represents the value as 5 uint64_t limbs in base
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* 2^52. */
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typedef struct {
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/* A field element f represents the sum(i=0..4, f.n[i] << (i*52)) mod p,
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* where p is the field modulus, 2^256 - 2^32 - 977.
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*
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* The individual limbs f.n[i] can exceed 2^52; the field's magnitude roughly
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* corresponds to how much excess is allowed. The value
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* sum(i=0..4, f.n[i] << (i*52)) may exceed p, unless the field element is
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* normalized. */
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uint64_t n[5];
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/*
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* Magnitude m requires:
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* n[i] <= 2 * m * (2^52 - 1) for i=0..3
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* n[4] <= 2 * m * (2^48 - 1)
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*
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* Normalized requires:
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* n[i] <= (2^52 - 1) for i=0..3
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* sum(i=0..4, n[i] << (i*52)) < p
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* (together these imply n[4] <= 2^48 - 1)
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*/
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SECP256K1_FE_VERIFY_FIELDS
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} secp256k1_fe;
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/* Unpacks a constant into a overlapping multi-limbed FE element. */
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#define SECP256K1_FE_CONST_INNER(d7, d6, d5, d4, d3, d2, d1, d0) { \
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(d0) | (((uint64_t)(d1) & 0xFFFFFUL) << 32), \
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((uint64_t)(d1) >> 20) | (((uint64_t)(d2)) << 12) | (((uint64_t)(d3) & 0xFFUL) << 44), \
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((uint64_t)(d3) >> 8) | (((uint64_t)(d4) & 0xFFFFFFFUL) << 24), \
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((uint64_t)(d4) >> 28) | (((uint64_t)(d5)) << 4) | (((uint64_t)(d6) & 0xFFFFUL) << 36), \
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((uint64_t)(d6) >> 16) | (((uint64_t)(d7)) << 16) \
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}
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typedef struct {
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uint64_t n[4];
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} secp256k1_fe_storage;
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#define SECP256K1_FE_STORAGE_CONST(d7, d6, d5, d4, d3, d2, d1, d0) {{ \
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(d0) | (((uint64_t)(d1)) << 32), \
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(d2) | (((uint64_t)(d3)) << 32), \
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(d4) | (((uint64_t)(d5)) << 32), \
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(d6) | (((uint64_t)(d7)) << 32) \
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}}
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#define SECP256K1_FE_STORAGE_CONST_GET(d) \
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(uint32_t)(d.n[3] >> 32), (uint32_t)d.n[3], \
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(uint32_t)(d.n[2] >> 32), (uint32_t)d.n[2], \
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(uint32_t)(d.n[1] >> 32), (uint32_t)d.n[1], \
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(uint32_t)(d.n[0] >> 32), (uint32_t)d.n[0]
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#endif /* SECP256K1_FIELD_REPR_H */
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