static int ecp_precompute_comb()

in Simulation/RIoT/Core/RIoTCrypt/ecp.c [1691:1821]

• 91 lines of code
• 28 McCabe index (conditional complexity)

static int ecp_precompute_comb( const mbedtls_ecp_group *grp,
                                mbedtls_ecp_point T[], const mbedtls_ecp_point *P,
                                unsigned char w, size_t d,
                                mbedtls_ecp_restart_ctx *rs_ctx )
{
    int ret;
    unsigned char i;
    size_t j = 0;
    const unsigned char T_size = 1U << ( w - 1 );
    mbedtls_ecp_point *cur, *TT[COMB_MAX_PRE - 1];

#if defined(MBEDTLS_ECP_RESTARTABLE)
    if( rs_ctx != NULL && rs_ctx->rsm != NULL )
    {
        if( rs_ctx->rsm->state == ecp_rsm_pre_dbl )
            goto dbl;
        if( rs_ctx->rsm->state == ecp_rsm_pre_norm_dbl )
            goto norm_dbl;
        if( rs_ctx->rsm->state == ecp_rsm_pre_add )
            goto add;
        if( rs_ctx->rsm->state == ecp_rsm_pre_norm_add )
            goto norm_add;
    }
#else
    (void) rs_ctx;
#endif

#if defined(MBEDTLS_ECP_RESTARTABLE)
    if( rs_ctx != NULL && rs_ctx->rsm != NULL )
    {
        rs_ctx->rsm->state = ecp_rsm_pre_dbl;

        /* initial state for the loop */
        rs_ctx->rsm->i = 0;
    }

dbl:
#endif
    /*
     * Set T[0] = P and
     * T[2^{l-1}] = 2^{dl} P for l = 1 .. w-1 (this is not the final value)
     */
    MBEDTLS_MPI_CHK( mbedtls_ecp_copy( &T[0], P ) );

#if defined(MBEDTLS_ECP_RESTARTABLE)
    if( rs_ctx != NULL && rs_ctx->rsm != NULL && rs_ctx->rsm->i != 0 )
        j = rs_ctx->rsm->i;
    else
#endif
        j = 0;

    for( ; j < d * ( w - 1 ); j++ )
    {
        MBEDTLS_ECP_BUDGET( MBEDTLS_ECP_OPS_DBL );

        i = 1U << ( j / d );
        cur = T + i;

        if( j % d == 0 )
            MBEDTLS_MPI_CHK( mbedtls_ecp_copy( cur, T + ( i >> 1 ) ) );

        MBEDTLS_MPI_CHK( ecp_double_jac( grp, cur, cur ) );
    }

#if defined(MBEDTLS_ECP_RESTARTABLE)
    if( rs_ctx != NULL && rs_ctx->rsm != NULL )
        rs_ctx->rsm->state = ecp_rsm_pre_norm_dbl;

norm_dbl:
#endif
    /*
     * Normalize current elements in T. As T has holes,
     * use an auxiliary array of pointers to elements in T.
     */
    j = 0;
    for( i = 1; i < T_size; i <<= 1 )
        TT[j++] = T + i;

    MBEDTLS_ECP_BUDGET( MBEDTLS_ECP_OPS_INV + 6 * j - 2 );

    MBEDTLS_MPI_CHK( ecp_normalize_jac_many( grp, TT, j ) );

#if defined(MBEDTLS_ECP_RESTARTABLE)
    if( rs_ctx != NULL && rs_ctx->rsm != NULL )
        rs_ctx->rsm->state = ecp_rsm_pre_add;

add:
#endif
    /*
     * Compute the remaining ones using the minimal number of additions
     * Be careful to update T[2^l] only after using it!
     */
    MBEDTLS_ECP_BUDGET( ( T_size - 1 ) * MBEDTLS_ECP_OPS_ADD );

    for( i = 1; i < T_size; i <<= 1 )
    {
        j = i;
        while( j-- )
            MBEDTLS_MPI_CHK( ecp_add_mixed( grp, &T[i + j], &T[j], &T[i] ) );
    }

#if defined(MBEDTLS_ECP_RESTARTABLE)
    if( rs_ctx != NULL && rs_ctx->rsm != NULL )
        rs_ctx->rsm->state = ecp_rsm_pre_norm_add;

norm_add:
#endif
    /*
     * Normalize final elements in T. Even though there are no holes now, we
     * still need the auxiliary array for homogeneity with the previous
     * call. Also, skip T[0] which is already normalised, being a copy of P.
     */
    for( j = 0; j + 1 < T_size; j++ )
        TT[j] = T + j + 1;

    MBEDTLS_ECP_BUDGET( MBEDTLS_ECP_OPS_INV + 6 * j - 2 );

    MBEDTLS_MPI_CHK( ecp_normalize_jac_many( grp, TT, j ) );

cleanup:
#if defined(MBEDTLS_ECP_RESTARTABLE)
    if( rs_ctx != NULL && rs_ctx->rsm != NULL &&
        ret == MBEDTLS_ERR_ECP_IN_PROGRESS )
    {
        if( rs_ctx->rsm->state == ecp_rsm_pre_dbl )
            rs_ctx->rsm->i = j;
    }
#endif

    return( ret );
}