/*
    Copyright (C) 2011 Sebastian Pancratz

    This file is part of FLINT.

    FLINT is free software: you can redistribute it and/or modify it under
    the terms of the GNU Lesser General Public License (LGPL) as published
    by the Free Software Foundation; either version 3 of the License, or
    (at your option) any later version.  See <https://www.gnu.org/licenses/>.
*/

#include "fmpz.h"
#include "fmpz_vec.h"
#include "fmpz_poly.h"
#include "fmpz_mod.h"
#include "fmpz_mod_poly.h"

void _fmpz_mod_poly_radix_init(fmpz **Rpow, fmpz **Rinv,
                    const fmpz *R, slong lenR, slong k,
                    const fmpz_t invL, const fmpz_mod_ctx_t ctx)
{
    const slong degR = lenR - 1;
    slong i;
    fmpz_t invLP;
    fmpz *W;

    fmpz_init_set(invLP, invL);
    W = flint_malloc((WORD(1) << (k - 1)) * degR * sizeof(fmpz));

    _fmpz_vec_set(Rpow[0], R, lenR);
    for (i = 1; i < k; i++)
    {
        _fmpz_mod_poly_sqr(Rpow[i], Rpow[i - 1], degR * (WORD(1) << (i - 1)) + 1, ctx);
    }

    for (i = 0; i < k; i++)
    {
        const slong lenQ = (WORD(1) << i) * degR;
        slong j;

        /* W := rev{Rpow[i], lenQ} */
        for (j = 0; j < lenQ; j++)
        {
            W[j] = Rpow[i][lenQ - j];
        }

/*
        TODO: _fmpz_mod_poly_inv_series no longer accepts a precomputed
              inverse leading coefficient; add back a version that does this.

        _fmpz_mod_poly_inv_series(Rinv[i], W, lenQ, invLP, ctx);
*/
        _fmpz_mod_poly_inv_series(Rinv[i], W, lenQ, lenQ, ctx);

        /* invLP := inv{lead{R^{2^i}}} */
        if (i != k - 1)
            fmpz_mod_mul(invLP, invLP, invLP, ctx);
    }

    fmpz_clear(invLP);
    flint_free(W);
}

void fmpz_mod_poly_radix_init(fmpz_mod_poly_radix_t D,
                 const fmpz_mod_poly_t R, slong degF, const fmpz_mod_ctx_t ctx)
{
    const slong degR = R->length - 1;

    if (degF < degR)
    {
        D->k = 0;
        D->degR = degR;
    }
    else
    {
        const slong N = degF / degR;
        const slong k = FLINT_BIT_COUNT(N);     /* k := ceil{log{N+1}} */
        const slong lenV = degR * ((WORD(1) << k) - 1) + k;
        const slong lenW = degR * ((WORD(1) << k) - 1);

        slong i;

        D->V = _fmpz_vec_init(lenV + lenW);
        D->W = D->V + lenV;

        D->Rpow = flint_malloc(k * sizeof(fmpz *));
        D->Rinv = flint_malloc(k * sizeof(fmpz *));

        for (i = 0; i < k; i++)
        {
            D->Rpow[i] = D->V + (degR * ((WORD(1) << i) - 1) + i);
            D->Rinv[i] = D->W + (degR * ((WORD(1) << i) - 1));
        }

        fmpz_init(&(D->invL));
        fmpz_invmod(&(D->invL), R->coeffs + degR, fmpz_mod_ctx_modulus(ctx));

        _fmpz_mod_poly_radix_init(D->Rpow, D->Rinv, R->coeffs, degR + 1,
                                  k, &(D->invL), ctx);

        D->k = k;
        D->degR = degR;
    }
}

void fmpz_mod_poly_radix_clear(fmpz_mod_poly_radix_t D)
{
    if (D->k)
    {
        const slong degR = D->degR;
        const slong k    = D->k;
        const slong lenV = degR * ((WORD(1) << k) - 1) + k;
        const slong lenW = degR * ((WORD(1) << k) - 1);

        _fmpz_vec_clear(D->V, lenV + lenW);
        flint_free(D->Rpow);
        flint_free(D->Rinv);
        fmpz_clear(&(D->invL));
    }
}

void _fmpz_mod_poly_radix(fmpz **B, const fmpz *F, fmpz **Rpow, fmpz **Rinv,
                          slong degR, slong k, slong i, fmpz *W, const fmpz_mod_ctx_t ctx)
{
    if (i == -1)
    {
        _fmpz_vec_set(B[k], F, degR);
    }
    else
    {
        const slong lenQ = (WORD(1) << i) * degR;

        fmpz *Frev = W;
        fmpz *Q    = W + lenQ;
        fmpz *S    = W;

        _fmpz_poly_reverse(Frev, F + lenQ, lenQ, lenQ);
        _fmpz_mod_poly_mullow(Q, Frev, lenQ, Rinv[i], lenQ, lenQ, ctx);
        _fmpz_poly_reverse(Q, Q, lenQ, lenQ);

        _fmpz_mod_poly_radix(B, Q, Rpow, Rinv, degR, k + (WORD(1) << i), i-1, W, ctx);

        _fmpz_mod_poly_mullow(S, Rpow[i], lenQ, Q, lenQ, lenQ, ctx);
        _fmpz_mod_poly_sub(S, F, lenQ, S, lenQ, ctx);

        _fmpz_mod_poly_radix(B, S, Rpow, Rinv, degR, k, i-1, W + lenQ, ctx);
    }
}

void fmpz_mod_poly_radix(fmpz_mod_poly_struct **B, const fmpz_mod_poly_t F,
                       const fmpz_mod_poly_radix_t D, const fmpz_mod_ctx_t ctx)
{
    const slong lenF = F->length;
    const slong degF = F->length - 1;
    const slong degR = D->degR;
    const slong N    = degF / degR;

    if (N == 0)
    {
        fmpz_mod_poly_set(B[0], F, ctx);
    }
    else
    {
        const slong k    = FLINT_BIT_COUNT(N);     /* k := ceil{log{N+1}}    */
        const slong lenG = (WORD(1) << k) * degR;       /* Padded size            */
        const slong t    = (lenG - 1) / degR - N;  /* Extra {degR}-blocks    */

        fmpz *G;                                  /* Padded copy of F       */
        fmpz *T;                                  /* Additional B[i]        */
        fmpz **C;                                 /* Enlarged version of B  */
        fmpz *W;                                  /* Temporary space        */

        slong i;

        if (lenF < lenG)
        {
            G = flint_malloc(lenG * sizeof(fmpz));
            for (i = 0; i < lenF; i++)
                G[i] = F->coeffs[i];
            flint_mpn_zero((mp_ptr) G + lenF, lenG - lenF);

            T = t ? _fmpz_vec_init(t * degR) : NULL;
        }
        else  /* lenF == lenG */
        {
            G = F->coeffs;
            T = NULL;
        }

        C = flint_malloc((N + 1 + t) * sizeof(fmpz *));
        for (i = 0; i <= N; i++)
        {
            fmpz_mod_poly_fit_length(B[i], degR, ctx);
            C[i] = B[i]->coeffs;
        }
        for (i = 0; i < t; i++)
        {
            C[N + 1 + i] = T + i * degR;
        }

        W = _fmpz_vec_init(lenG);

        _fmpz_mod_poly_radix(C, G, D->Rpow, D->Rinv, degR, 0, k-1, W, ctx);

        _fmpz_vec_clear(W, lenG);

        for (i = 0; i <= N; i++)
        {
            _fmpz_mod_poly_set_length(B[i], degR);
            _fmpz_mod_poly_normalise(B[i]);
        }
        flint_free(C);
        if (lenF < lenG)
        {
            flint_free(G);
        }
        if (t)
        {
            _fmpz_vec_clear(T, t * degR);
        }
    }
}
