github.com/ethereum/go-ethereum@v1.16.1/crypto/secp256k1/libsecp256k1/src/modinv64.h (about)

     1  /***********************************************************************
     2   * Copyright (c) 2020 Peter Dettman                                    *
     3   * Distributed under the MIT software license, see the accompanying    *
     4   * file COPYING or https://www.opensource.org/licenses/mit-license.php.*
     5   **********************************************************************/
     6  
     7  #ifndef SECP256K1_MODINV64_H
     8  #define SECP256K1_MODINV64_H
     9  
    10  #include "util.h"
    11  
    12  #ifndef SECP256K1_WIDEMUL_INT128
    13  #error "modinv64 requires 128-bit wide multiplication support"
    14  #endif
    15  
    16  /* A signed 62-bit limb representation of integers.
    17   *
    18   * Its value is sum(v[i] * 2^(62*i), i=0..4). */
    19  typedef struct {
    20      int64_t v[5];
    21  } secp256k1_modinv64_signed62;
    22  
    23  typedef struct {
    24      /* The modulus in signed62 notation, must be odd and in [3, 2^256]. */
    25      secp256k1_modinv64_signed62 modulus;
    26  
    27      /* modulus^{-1} mod 2^62 */
    28      uint64_t modulus_inv62;
    29  } secp256k1_modinv64_modinfo;
    30  
    31  /* Replace x with its modular inverse mod modinfo->modulus. x must be in range [0, modulus).
    32   * If x is zero, the result will be zero as well. If not, the inverse must exist (i.e., the gcd of
    33   * x and modulus must be 1). These rules are automatically satisfied if the modulus is prime.
    34   *
    35   * On output, all of x's limbs will be in [0, 2^62).
    36   */
    37  static void secp256k1_modinv64_var(secp256k1_modinv64_signed62 *x, const secp256k1_modinv64_modinfo *modinfo);
    38  
    39  /* Same as secp256k1_modinv64_var, but constant time in x (not in the modulus). */
    40  static void secp256k1_modinv64(secp256k1_modinv64_signed62 *x, const secp256k1_modinv64_modinfo *modinfo);
    41  
    42  /* Compute the Jacobi symbol for (x | modinfo->modulus). x must be coprime with modulus (and thus
    43   * cannot be 0, as modulus >= 3). All limbs of x must be non-negative. Returns 0 if the result
    44   * cannot be computed. */
    45  static int secp256k1_jacobi64_maybe_var(const secp256k1_modinv64_signed62 *x, const secp256k1_modinv64_modinfo *modinfo);
    46  
    47  #endif /* SECP256K1_MODINV64_H */