/*
    Copyright (C) 2008, 2009 William Hart
    Copyright (C) 2010 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 2.1 of the License, or
    (at your option) any later version.  See <https://www.gnu.org/licenses/>.
*/

#include <stdlib.h>
#include <gmp.h>
#include "flint.h"
#include "fmpz.h"
#include "fmpz_vec.h"
#include "fmpz_poly.h"

void
_fmpz_poly_mullow_tiny1(fmpz * res, const fmpz * poly1,
                         slong len1, const fmpz * poly2, slong len2, slong n)
{
    slong i, j, c;

    _fmpz_vec_zero(res, n);

    for (i = 0; i < len1; i++)
    {
        c = poly1[i];

        if (c != 0)
        {
            for (j = 0; j < FLINT_MIN(len2, n - i); j++)
                res[i + j] += c * poly2[j];
        }
    }
}

void
_fmpz_poly_mullow_tiny2(fmpz * res, const fmpz * poly1,
                         slong len1, const fmpz * poly2, slong len2, slong n)
{
    slong i, j, k, c, d;
    mp_limb_t hi, lo;
    mp_ptr tmp;
    TMP_INIT;

    TMP_START;

    tmp = TMP_ALLOC(2 * n * sizeof(mp_limb_t));

    flint_mpn_zero(tmp, 2 * n);

    for (i = 0; i < len1; i++)
    {
        c = poly1[i];

        if (c != 0)
        {
            for (j = 0; j < FLINT_MIN(len2, n - i); j++)
            {
                k = i + j;

                d = poly2[j];

                if (d != 0)
                {
                    smul_ppmm(hi, lo, c, d);
                    add_ssaaaa(tmp[2 * k + 1], tmp[2 * k],
                               tmp[2 * k + 1], tmp[2 * k], hi, lo);
                }
            }
        }
    }

    for (i = 0; i < n; i++)
    {
        lo = tmp[2 * i];
        hi = tmp[2 * i + 1];

        if (((mp_limb_signed_t) hi) >= 0)
        {
            fmpz_set_uiui(res + i, hi, lo);
        }
        else
        {
            sub_ddmmss(hi, lo, 0, 0, hi, lo);
            fmpz_neg_uiui(res + i, hi, lo);
        }
    }

    TMP_END;
    return;
}

void
_fmpz_poly_mullow(fmpz * res, const fmpz * poly1, slong len1, 
                                const fmpz * poly2, slong len2, slong n)
{
    mp_size_t limbs1, limbs2;
    slong bits1, bits2, rbits;

    len1 = FLINT_MIN(len1, n);
    len2 = FLINT_MIN(len2, n);

    if (len2 == 1)
    {
        _fmpz_vec_scalar_mul_fmpz(res, poly1, len1, poly2);
        return;
    }

    if (poly1 == poly2 && len1 == len2)
    {
        _fmpz_poly_sqrlow(res, poly1, len1, n);
        return;
    }

    bits1 = _fmpz_vec_max_bits(poly1, len1);
    bits2 = _fmpz_vec_max_bits(poly2, len2);
    bits1 = FLINT_ABS(bits1);
    bits2 = FLINT_ABS(bits2);

    if (bits1 <= FLINT_BITS - 2 && bits2 <= FLINT_BITS - 2 &&
        (len2 < 50 || (4 * len2 >= 3 * n && n < 150 + bits1 + bits2)))
    {
        rbits = bits1 + bits2 + FLINT_BIT_COUNT(len2);

        if (rbits <= FLINT_BITS - 2)
        {
            _fmpz_poly_mullow_tiny1(res, poly1, len1, poly2, len2, n);
            return;
        }
        else if (rbits <= 2 * FLINT_BITS - 1)
        {
            _fmpz_poly_mullow_tiny2(res, poly1, len1, poly2, len2, n);
            return;
        }
    }

    if (len2 < 7)
    {
        _fmpz_poly_mullow_classical(res, poly1, len1, poly2, len2, n);
        return;
    }

    limbs1 = (bits1 + FLINT_BITS - 1) / FLINT_BITS;
    limbs2 = (bits2 + FLINT_BITS - 1) / FLINT_BITS;

    if (n < 16 && (limbs1 > 12 || limbs2 > 12))
    {
        int clear = 0, i;
        fmpz *copy1, *copy2;

        if (len1 >= n)
            copy1 = (fmpz *) poly1;
        else
        {
            copy1 = (fmpz *) flint_malloc(n * sizeof(fmpz));
            for (i = 0; i < len1; i++)
                copy1[i] = poly1[i];
            flint_mpn_zero((mp_ptr) copy1 + len1, n - len1);
            clear |= 1;
        }

        if (len2 >= n)
            copy2 = (fmpz *) poly2;
        else
        {
            copy2 = (fmpz *) flint_malloc(n * sizeof(fmpz));
            for (i = 0; i < len2; i++)
                copy2[i] = poly2[i];
            flint_mpn_zero((mp_ptr) copy2 + len2, n - len2);
            clear |= 2;
        }

        _fmpz_poly_mullow_karatsuba_n(res, copy1, copy2, n);

        if (clear & 1)
            flint_free(copy1);
        if (clear & 2)
            flint_free(copy2);
    }
    else if (limbs1 + limbs2 <= 8)
        _fmpz_poly_mullow_KS(res, poly1, len1, poly2, len2, n);
    else if ((limbs1+limbs2)/2048 > len1 + len2)
        _fmpz_poly_mullow_KS(res, poly1, len1, poly2, len2, n);
    else if ((limbs1 + limbs2)*FLINT_BITS*4 < len1 + len2)
        _fmpz_poly_mullow_KS(res, poly1, len1, poly2, len2, n);
    else
        _fmpz_poly_mullow_SS(res, poly1, len1, poly2, len2, n);
}

void
fmpz_poly_mullow(fmpz_poly_t res,
                   const fmpz_poly_t poly1, const fmpz_poly_t poly2,
                   slong n)
{
    const slong len1 = poly1->length;
    const slong len2 = poly2->length;

    if (len1 == 0 || len2 == 0 || n == 0)
    {
        fmpz_poly_zero(res);
        return;
    }

    if (res == poly1 || res == poly2)
    {
        fmpz_poly_t t;
        fmpz_poly_init2(t, n);
        fmpz_poly_mullow(t, poly1, poly2, n);
        fmpz_poly_swap(res, t);
        fmpz_poly_clear(t);
        return;
    }

    n = FLINT_MIN(n, len1 + len2 - 1);

    fmpz_poly_fit_length(res, n);
    if (len1 >= len2)
        _fmpz_poly_mullow(res->coeffs, poly1->coeffs, len1, poly2->coeffs, len2, n);
    else
        _fmpz_poly_mullow(res->coeffs, poly2->coeffs, len2, poly1->coeffs, len1, n);
    _fmpz_poly_set_length(res, n);
    _fmpz_poly_normalise(res);
}