flint-sys 0.9.0

Bindings to the FLINT C library
Documentation 
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/*
    Copyright (C) 2014 William Hart

    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_mod.h"
#include "fmpz_mod_poly.h"

void
_fmpz_mod_poly_discriminant(fmpz_t d, const fmpz *poly, slong len, const fmpz_mod_ctx_t ctx)
{
   fmpz *der = _fmpz_vec_init(len - 1);
   slong dlen = len - 1, exp;
   fmpz_t pow;

   _fmpz_mod_poly_derivative(der, poly, len, ctx);
   FMPZ_VEC_NORM(der, dlen);

   if (dlen == 0)
   {
      fmpz_zero(d);
   } else
   {
      fmpz_init(pow);

      _fmpz_mod_poly_resultant(d, poly, len, der, dlen, ctx);
      exp = len - dlen - 2;

      if (exp >= 0)
         fmpz_mod_pow_ui(pow, poly + len - 1, exp, ctx);
      else
         fmpz_mod_inv(pow, poly + len - 1, ctx);

      fmpz_mod_mul(d, d, pow, ctx);

      if ((len & 3) == 0 || (len & 3) == 3) /* degree is not 0, 1 mod 4 */
         fmpz_mod_neg(d, d, ctx);

      fmpz_clear(pow);
   }

   _fmpz_vec_clear(der, len - 1);
}

void fmpz_mod_poly_discriminant(fmpz_t d, const fmpz_mod_poly_t f,
                                                      const fmpz_mod_ctx_t ctx)
{
    const slong len = f->length;

    if (len <= 1)
        fmpz_zero(d);
    else
       _fmpz_mod_poly_discriminant(d, f->coeffs, len, ctx);
}