/*
    Copyright (C) 2013-2014 Fredrik Johansson

    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 "arb.h"
#include "partitions.h"

#ifdef __GNUC__
# define sqrt __builtin_sqrt
#else
# include <math.h>
#endif

/* This nice round number precisely fits on 32 bits */
#define NUMBER_OF_SMALL_PARTITIONS 128

const unsigned int
partitions_lookup[NUMBER_OF_SMALL_PARTITIONS] =
{
    UWORD(1),UWORD(1),UWORD(2),UWORD(3),UWORD(5),UWORD(7),UWORD(11),UWORD(15),UWORD(22),UWORD(30),UWORD(42),UWORD(56),UWORD(77),UWORD(101),UWORD(135),
    UWORD(176),UWORD(231),UWORD(297),UWORD(385),UWORD(490),UWORD(627),UWORD(792),UWORD(1002),UWORD(1255),UWORD(1575),UWORD(1958),
    UWORD(2436),UWORD(3010),UWORD(3718),UWORD(4565),UWORD(5604),UWORD(6842),UWORD(8349),UWORD(10143),UWORD(12310),UWORD(14883),
    UWORD(17977),UWORD(21637),UWORD(26015),UWORD(31185),UWORD(37338),UWORD(44583),UWORD(53174),UWORD(63261),UWORD(75175),
    UWORD(89134),UWORD(105558),UWORD(124754),UWORD(147273),UWORD(173525),UWORD(204226),UWORD(239943),UWORD(281589),
    UWORD(329931),UWORD(386155),UWORD(451276),UWORD(526823),UWORD(614154),UWORD(715220),UWORD(831820),UWORD(966467),
    UWORD(1121505),UWORD(1300156),UWORD(1505499),UWORD(1741630),UWORD(2012558),UWORD(2323520),UWORD(2679689),
    UWORD(3087735),UWORD(3554345),UWORD(4087968),UWORD(4697205),UWORD(5392783),UWORD(6185689),UWORD(7089500),
    UWORD(8118264),UWORD(9289091),UWORD(10619863),UWORD(12132164),UWORD(13848650),UWORD(15796476),UWORD(18004327),
    UWORD(20506255),UWORD(23338469),UWORD(26543660),UWORD(30167357),UWORD(34262962),UWORD(38887673),
    UWORD(44108109),UWORD(49995925),UWORD(56634173),UWORD(64112359),UWORD(72533807),UWORD(82010177),
    UWORD(92669720),UWORD(104651419),UWORD(118114304),UWORD(133230930),UWORD(150198136),UWORD(169229875),
    UWORD(190569292),UWORD(214481126),UWORD(241265379),UWORD(271248950),UWORD(304801365),UWORD(342325709),
    UWORD(384276336),UWORD(431149389),UWORD(483502844),UWORD(541946240),UWORD(607163746),UWORD(679903203),
    UWORD(761002156),UWORD(851376628),UWORD(952050665),UWORD(1064144451),UWORD(1188908248),UWORD(1327710076),
    UWORD(1482074143),UWORD(1653668665),UWORD(1844349560),UWORD(2056148051),UWORD(2291320912),
    UWORD(2552338241),UWORD(2841940500),UWORD(3163127352),UWORD(3519222692),UWORD(3913864295)
};

slong partitions_hrr_needed_terms(double n);

void
partitions_fmpz_fmpz_hrr(fmpz_t p, const fmpz_t n, int use_doubles)
{
    arb_t x;
    arf_t bound;
    slong N;

    arb_init(x);
    arf_init(bound);

    N = partitions_hrr_needed_terms(fmpz_get_d(n));

    partitions_hrr_sum_arb(x, n, 1, N, use_doubles);

    partitions_rademacher_bound(bound, n, N);
    arb_add_error_arf(x, bound);

    if (!arb_get_unique_fmpz(p, x))
    {
        flint_throw(FLINT_ERROR, "not unique!\n%s\n", arb_get_str(x, 50, 0));
    }

    arb_clear(x);
    arf_clear(bound);
}

/* To compute p(n) mod 2^64. */
static void
partitions_vec(nn_ptr v, slong len)
{
    slong i, j, n;
    ulong p;

    for (n = 0; n < FLINT_MIN(len, NUMBER_OF_SMALL_PARTITIONS); n++)
        v[n] = partitions_lookup[n];

    for (n = NUMBER_OF_SMALL_PARTITIONS; n < len; n++)
    {
        p = 0;
        for (i = 1, j = 1; j <= n; j += 3 * i + 1, i++)
            p = v[n - j] - p;
        if ((i & 1) == 0)
            p = -p;
        for (i = 1, j = 2; j <= n; j += 3 * i + 2, i++)
            p = v[n - j] - p;
        if ((i & 1) != 0)
            p = -p;
        v[n] = p;
    }
}

/* The floor+vec method *requires* n <= 1498 for floor(p(n)/2^64)
   to be equal to floor(T/2^64). It is faster up to n ~= 1200.
   With doubles, it is faster up to n ~= 500. */
void
_partitions_fmpz_ui(fmpz_t res, ulong n, int use_doubles)
{
    if (n < NUMBER_OF_SMALL_PARTITIONS)
    {
        fmpz_set_ui(res, partitions_lookup[n]);
    }
    else if (FLINT_BITS == 64 && (n < 500 || (!use_doubles && n < 1200)))
    {
        nn_ptr tmp = flint_malloc((n + 1) * sizeof(ulong));

        if (n < 417)  /* p(n) < 2^64 */
        {
            partitions_vec(tmp, n + 1);
            fmpz_set_ui(res, tmp[n]);
        }
        else
        {
            arb_t x;
            arb_init(x);
            fmpz_set_ui(res, n);
            partitions_leading_fmpz(x, res, 4 * sqrt(n) - 50);
            arb_mul_2exp_si(x, x, -64);
            arb_floor(x, x, 4 * sqrt(n) - 50);

            if (arb_get_unique_fmpz(res, x))
            {
                fmpz_mul_2exp(res, res, 64);
                partitions_vec(tmp, n + 1);
                fmpz_add_ui(res, res, tmp[n]);
            }
            else
            {
                flint_printf("warning: failed at %wu\n", n);
                fmpz_set_ui(res, n);
                partitions_fmpz_fmpz_hrr(res, res, use_doubles);
            }
            arb_clear(x);
        }
        flint_free(tmp);
    }
    else
    {
        fmpz_set_ui(res, n);
        partitions_fmpz_fmpz_hrr(res, res, use_doubles);
    }
}

void
partitions_fmpz_fmpz(fmpz_t res, const fmpz_t n, int use_doubles)
{
    if (fmpz_cmp_ui(n, 2000) < 0)
    {
        if (fmpz_sgn(n) < 0)
            fmpz_zero(res);
        else
            _partitions_fmpz_ui(res, *n, use_doubles);
    }
    else
    {
        partitions_fmpz_fmpz_hrr(res, n, use_doubles);
    }
}

void
partitions_fmpz_ui(fmpz_t res, ulong n)
{
    _partitions_fmpz_ui(res, n, 0);
}
