int mbedtls_mpi_div_mpi()

in Simulation/RIoT/Core/RIoTCrypt/bignum.c [1629:1742]

• 94 lines of code
• 17 McCabe index (conditional complexity)

int mbedtls_mpi_div_mpi( mbedtls_mpi *Q, mbedtls_mpi *R, const mbedtls_mpi *A,
                         const mbedtls_mpi *B )
{
    int ret;
    size_t i, n, t, k;
    mbedtls_mpi X, Y, Z, T1, T2;
    MPI_VALIDATE_RET( A != NULL );
    MPI_VALIDATE_RET( B != NULL );

    if( mbedtls_mpi_cmp_int( B, 0 ) == 0 )
        return( MBEDTLS_ERR_MPI_DIVISION_BY_ZERO );

    mbedtls_mpi_init( &X ); mbedtls_mpi_init( &Y ); mbedtls_mpi_init( &Z );
    mbedtls_mpi_init( &T1 ); mbedtls_mpi_init( &T2 );

    if( mbedtls_mpi_cmp_abs( A, B ) < 0 )
    {
        if( Q != NULL ) MBEDTLS_MPI_CHK( mbedtls_mpi_lset( Q, 0 ) );
        if( R != NULL ) MBEDTLS_MPI_CHK( mbedtls_mpi_copy( R, A ) );
        return( 0 );
    }

    MBEDTLS_MPI_CHK( mbedtls_mpi_copy( &X, A ) );
    MBEDTLS_MPI_CHK( mbedtls_mpi_copy( &Y, B ) );
    X.s = Y.s = 1;

    MBEDTLS_MPI_CHK( mbedtls_mpi_grow( &Z, A->n + 2 ) );
    MBEDTLS_MPI_CHK( mbedtls_mpi_lset( &Z,  0 ) );
    MBEDTLS_MPI_CHK( mbedtls_mpi_grow( &T1, 2 ) );
    MBEDTLS_MPI_CHK( mbedtls_mpi_grow( &T2, 3 ) );

    k = mbedtls_mpi_bitlen( &Y ) % biL;
    if( k < biL - 1 )
    {
        k = biL - 1 - k;
        MBEDTLS_MPI_CHK( mbedtls_mpi_shift_l( &X, k ) );
        MBEDTLS_MPI_CHK( mbedtls_mpi_shift_l( &Y, k ) );
    }
    else k = 0;

    n = X.n - 1;
    t = Y.n - 1;
    MBEDTLS_MPI_CHK( mbedtls_mpi_shift_l( &Y, biL * ( n - t ) ) );

    while( mbedtls_mpi_cmp_mpi( &X, &Y ) >= 0 )
    {
        Z.p[n - t]++;
        MBEDTLS_MPI_CHK( mbedtls_mpi_sub_mpi( &X, &X, &Y ) );
    }
    MBEDTLS_MPI_CHK( mbedtls_mpi_shift_r( &Y, biL * ( n - t ) ) );

    for( i = n; i > t ; i-- )
    {
        if( X.p[i] >= Y.p[t] )
            Z.p[i - t - 1] = (mbedtls_mpi_uint)~0;
        else
        {
            Z.p[i - t - 1] = mbedtls_int_div_int( X.p[i], X.p[i - 1],
                                                            Y.p[t], NULL);
        }

        Z.p[i - t - 1]++;
        do
        {
            Z.p[i - t - 1]--;

            MBEDTLS_MPI_CHK( mbedtls_mpi_lset( &T1, 0 ) );
            T1.p[0] = ( t < 1 ) ? 0 : Y.p[t - 1];
            T1.p[1] = Y.p[t];
            MBEDTLS_MPI_CHK( mbedtls_mpi_mul_int( &T1, &T1, Z.p[i - t - 1] ) );

            MBEDTLS_MPI_CHK( mbedtls_mpi_lset( &T2, 0 ) );
            T2.p[0] = ( i < 2 ) ? 0 : X.p[i - 2];
            T2.p[1] = ( i < 1 ) ? 0 : X.p[i - 1];
            T2.p[2] = X.p[i];
        }
        while( mbedtls_mpi_cmp_mpi( &T1, &T2 ) > 0 );

        MBEDTLS_MPI_CHK( mbedtls_mpi_mul_int( &T1, &Y, Z.p[i - t - 1] ) );
        MBEDTLS_MPI_CHK( mbedtls_mpi_shift_l( &T1,  biL * ( i - t - 1 ) ) );
        MBEDTLS_MPI_CHK( mbedtls_mpi_sub_mpi( &X, &X, &T1 ) );

        if( mbedtls_mpi_cmp_int( &X, 0 ) < 0 )
        {
            MBEDTLS_MPI_CHK( mbedtls_mpi_copy( &T1, &Y ) );
            MBEDTLS_MPI_CHK( mbedtls_mpi_shift_l( &T1, biL * ( i - t - 1 ) ) );
            MBEDTLS_MPI_CHK( mbedtls_mpi_add_mpi( &X, &X, &T1 ) );
            Z.p[i - t - 1]--;
        }
    }

    if( Q != NULL )
    {
        MBEDTLS_MPI_CHK( mbedtls_mpi_copy( Q, &Z ) );
        Q->s = A->s * B->s;
    }

    if( R != NULL )
    {
        MBEDTLS_MPI_CHK( mbedtls_mpi_shift_r( &X, k ) );
        X.s = A->s;
        MBEDTLS_MPI_CHK( mbedtls_mpi_copy( R, &X ) );

        if( mbedtls_mpi_cmp_int( R, 0 ) == 0 )
            R->s = 1;
    }

cleanup:

    mbedtls_mpi_free( &X ); mbedtls_mpi_free( &Y ); mbedtls_mpi_free( &Z );
    mbedtls_mpi_free( &T1 ); mbedtls_mpi_free( &T2 );

    return( ret );
}