github.com/ethereum/go-ethereum@v1.16.1/crypto/secp256k1/libsecp256k1/src/modinv32.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_MODINV32_H
     8  #define SECP256K1_MODINV32_H
     9  
    10  #include "util.h"
    11  
    12  /* A signed 30-bit limb representation of integers.
    13   *
    14   * Its value is sum(v[i] * 2^(30*i), i=0..8). */
    15  typedef struct {
    16      int32_t v[9];
    17  } secp256k1_modinv32_signed30;
    18  
    19  typedef struct {
    20      /* The modulus in signed30 notation, must be odd and in [3, 2^256]. */
    21      secp256k1_modinv32_signed30 modulus;
    22  
    23      /* modulus^{-1} mod 2^30 */
    24      uint32_t modulus_inv30;
    25  } secp256k1_modinv32_modinfo;
    26  
    27  /* Replace x with its modular inverse mod modinfo->modulus. x must be in range [0, modulus).
    28   * If x is zero, the result will be zero as well. If not, the inverse must exist (i.e., the gcd of
    29   * x and modulus must be 1). These rules are automatically satisfied if the modulus is prime.
    30   *
    31   * On output, all of x's limbs will be in [0, 2^30).
    32   */
    33  static void secp256k1_modinv32_var(secp256k1_modinv32_signed30 *x, const secp256k1_modinv32_modinfo *modinfo);
    34  
    35  /* Same as secp256k1_modinv32_var, but constant time in x (not in the modulus). */
    36  static void secp256k1_modinv32(secp256k1_modinv32_signed30 *x, const secp256k1_modinv32_modinfo *modinfo);
    37  
    38  /* Compute the Jacobi symbol for (x | modinfo->modulus). x must be coprime with modulus (and thus
    39   * cannot be 0, as modulus >= 3). All limbs of x must be non-negative. Returns 0 if the result
    40   * cannot be computed. */
    41  static int secp256k1_jacobi32_maybe_var(const secp256k1_modinv32_signed30 *x, const secp256k1_modinv32_modinfo *modinfo);
    42  
    43  #endif /* SECP256K1_MODINV32_H */