C++ (Cpp) mpi_tdiv_q_2exp Examples

Example #1

File: primegen.c Project: EmeraldViewer/EmeraldViewer

/*
 * Return true if n is probably a prime
 */
static int
is_prime (gcry_mpi_t n, int steps, unsigned int *count)
{
  gcry_mpi_t x = mpi_alloc( mpi_get_nlimbs( n ) );
  gcry_mpi_t y = mpi_alloc( mpi_get_nlimbs( n ) );
  gcry_mpi_t z = mpi_alloc( mpi_get_nlimbs( n ) );
  gcry_mpi_t nminus1 = mpi_alloc( mpi_get_nlimbs( n ) );
  gcry_mpi_t a2 = mpi_alloc_set_ui( 2 );
  gcry_mpi_t q;
  unsigned i, j, k;
  int rc = 0;
  unsigned nbits = mpi_get_nbits( n );

  mpi_sub_ui( nminus1, n, 1 );

  /* Find q and k, so that n = 1 + 2^k * q . */
  q = mpi_copy ( nminus1 );
  k = mpi_trailing_zeros ( q );
  mpi_tdiv_q_2exp (q, q, k);

  for (i=0 ; i < steps; i++ )
    {
      ++*count;
      if( !i )
        {
          mpi_set_ui( x, 2 );
        }
      else
        {
          gcry_mpi_randomize( x, nbits, GCRY_WEAK_RANDOM );

          /* Make sure that the number is smaller than the prime and
             keep the randomness of the high bit. */
          if ( mpi_test_bit ( x, nbits-2) )
            {
              mpi_set_highbit ( x, nbits-2); /* Clear all higher bits. */
            }
          else
            {
              mpi_set_highbit( x, nbits-2 );
              mpi_clear_bit( x, nbits-2 );
            }
          assert ( mpi_cmp( x, nminus1 ) < 0 && mpi_cmp_ui( x, 1 ) > 0 );
	}
      gcry_mpi_powm ( y, x, q, n);
      if ( mpi_cmp_ui(y, 1) && mpi_cmp( y, nminus1 ) )
        {
          for ( j=1; j < k && mpi_cmp( y, nminus1 ); j++ )
            {
              gcry_mpi_powm(y, y, a2, n);
              if( !mpi_cmp_ui( y, 1 ) )
                goto leave; /* Not a prime. */
            }
          if (mpi_cmp( y, nminus1 ) )
            goto leave; /* Not a prime. */
	}
      progress('+');
    }
  rc = 1; /* May be a prime. */

 leave:
  mpi_free( x );
  mpi_free( y );
  mpi_free( z );
  mpi_free( nminus1 );
  mpi_free( q );
  mpi_free( a2 );

  return rc;
}

Example #2

File: primegen.c Project: BridgeNY/purdue

/****************
 * Return true if n is probably a prime
 */
static int
is_prime( MPI n, int steps, int *count )
{
    MPI x = mpi_alloc( mpi_get_nlimbs( n ) );
    MPI y = mpi_alloc( mpi_get_nlimbs( n ) );
    MPI z = mpi_alloc( mpi_get_nlimbs( n ) );
    MPI nminus1 = mpi_alloc( mpi_get_nlimbs( n ) );
    MPI a2 = mpi_alloc_set_ui( 2 );
    MPI q;
    unsigned i, j, k;
    int rc = 0;
    unsigned nbits = mpi_get_nbits( n );

    mpi_sub_ui( nminus1, n, 1 );

    /* find q and k, so that n = 1 + 2^k * q */
    q = mpi_copy( nminus1 );
    k = mpi_trailing_zeros( q );
    mpi_tdiv_q_2exp(q, q, k);

    for(i=0 ; i < steps; i++ ) {
	++*count;
	if( !i ) {
	    mpi_set_ui( x, 2 );
	}
	else {
	    /*mpi_set_bytes( x, nbits-1, get_random_byte, 0 );*/
	    {	char *p = get_random_bits( nbits, 0, 0 );
		mpi_set_buffer( x, p, (nbits+7)/8, 0 );
		m_free(p);
	    }
	    /* make sure that the number is smaller than the prime
	     * and keep the randomness of the high bit */
	    if( mpi_test_bit( x, nbits-2 ) ) {
		mpi_set_highbit( x, nbits-2 ); /* clear all higher bits */
	    }
	    else {
		mpi_set_highbit( x, nbits-2 );
		mpi_clear_bit( x, nbits-2 );
	    }
	    assert( mpi_cmp( x, nminus1 ) < 0 && mpi_cmp_ui( x, 1 ) > 0 );
	}
	mpi_powm( y, x, q, n);
	if( mpi_cmp_ui(y, 1) && mpi_cmp( y, nminus1 ) ) {
	    for( j=1; j < k && mpi_cmp( y, nminus1 ); j++ ) {
		mpi_powm(y, y, a2, n);
		if( !mpi_cmp_ui( y, 1 ) )
		    goto leave; /* not a prime */
	    }
	    if( mpi_cmp( y, nminus1 ) )
		goto leave; /* not a prime */
	}
	progress('+');
    }
    rc = 1; /* may be a prime */

  leave:
    mpi_free( x );
    mpi_free( y );
    mpi_free( z );
    mpi_free( nminus1 );
    mpi_free( q );

    return rc;
}