/*
    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 2.1 of the License, or
    (at your option) any later version.  See <https://www.gnu.org/licenses/>.
*/

#include <gmp.h>
#include "flint.h"
#include "fmpz.h"
#include "fmpz_poly.h"
#include "fmpz_mod_poly.h"

void _fmpz_mod_poly_scalar_div_fmpz(fmpz *res, const fmpz *poly, slong len, 
                                    const fmpz_t x, const fmpz_t p)
{
    fmpz_t g, xinv;

    fmpz_init(g);
    fmpz_init(xinv);

    if (fmpz_sgn(x) < 0 || fmpz_cmp(x, p) >= 0)
    {
       fmpz_mod(xinv, x, p);
       fmpz_gcdinv(g, xinv, xinv, p);
    } else
       fmpz_gcdinv(g, xinv, x, p);

    if (!fmpz_is_one(g))
    {
        flint_printf("Exception (_fmpz_mod_poly_scalar_div_fmpz). Impossible inverse.\n");
        flint_abort();
    }

    _fmpz_vec_scalar_mul_fmpz(res, poly, len, xinv);
    _fmpz_vec_scalar_mod_fmpz(res, res, len, p);

    fmpz_clear(xinv);
    fmpz_clear(g);
}

void fmpz_mod_poly_scalar_div_fmpz(fmpz_mod_poly_t res,
          const fmpz_mod_poly_t poly, const fmpz_t x, const fmpz_mod_ctx_t ctx)
{

    if (fmpz_is_zero(x))
    {
        if (fmpz_is_one(fmpz_mod_ctx_modulus(ctx)))
        {
            fmpz_mod_poly_set(res, poly, ctx);
            return;
        }
        else
        {
            flint_printf("Exception (fmpz_mod_poly_scalar_div_fmpz). Division by zero.\n");
            flint_abort();
        }
    }

    fmpz_mod_poly_fit_length(res, poly->length, ctx);
    _fmpz_mod_poly_scalar_div_fmpz(res->coeffs, poly->coeffs, poly->length,
                                                 x, fmpz_mod_ctx_modulus(ctx));

    _fmpz_mod_poly_set_length(res, poly->length);
    _fmpz_mod_poly_normalise(res);
}