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/*=============================================================================
This file is part of FLINT.
FLINT is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 2 of the License, or
(at your option) any later version.
FLINT is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with FLINT; if not, write to the Free Software
Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
=============================================================================*/
/******************************************************************************
Copyright (C) 2011 William Hart
Copyright (C) 2012 Sebastian Pancratz
Copyright (C) 2013 Mike Hansen
******************************************************************************/
#include "fq.h"
void
fq_gcdinv(fq_t rop, fq_t inv, const fq_t op, const fq_ctx_t ctx)
{
fmpz *g, *s;
slong lenG;
if (fq_is_zero(op, ctx))
{
fq_zero(rop, ctx);
return;
}
if (rop == op)
{
g = _fmpz_vec_init(op->length);
}
else
{
fmpz_poly_fit_length(rop, op->length);
g = rop->coeffs;
}
if (inv == op)
{
s = _fmpz_vec_init(ctx->modulus->length - 1);
}
else
{
fmpz_poly_fit_length(inv, ctx->modulus->length - 1);
s = inv->coeffs;
}
lenG = _fmpz_mod_poly_gcdinv(g, s, op->coeffs, op->length,
ctx->modulus->coeffs, ctx->modulus->length,
fq_ctx_prime(ctx));
if (rop == op)
{
_fmpz_vec_clear(rop->coeffs, rop->alloc);
rop->coeffs = g;
rop->alloc = op->length;
}
if (inv == op)
{
_fmpz_vec_clear(inv->coeffs, inv->alloc);
inv->coeffs = s;
inv->alloc = ctx->modulus->length - 1;
}
_fmpz_poly_set_length(rop, lenG);
_fmpz_poly_set_length(inv, ctx->modulus->length - lenG);
_fmpz_poly_normalise(inv);
if (!fmpz_is_one(fmpz_poly_lead(rop)))
{
fmpz_t invG;
fmpz_init(invG);
fmpz_invmod(invG, fmpz_poly_lead(rop), fq_ctx_prime(ctx));
_fmpz_mod_poly_scalar_mul_fmpz(rop->coeffs, rop->coeffs, rop->length,
invG, fq_ctx_prime(ctx));
_fmpz_mod_poly_scalar_mul_fmpz(inv->coeffs, inv->coeffs, inv->length,
invG, fq_ctx_prime(ctx));
fmpz_clear(invG);
}
}
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