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/*
Copyright (C) 2011, 2012 Sebastian Pancratz
Copyright (C) 2012 Andres Goens
Copyright (C) 2013 Mike Hansen
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_poly.h"
#include "fmpz_mod_poly.h"
#include "fq.h"
static void
_fq_inv(fmpz * rop, const fmpz * op, slong len, const fq_ctx_t ctx)
{
const slong d = fq_ctx_degree(ctx);
if (len == 1)
{
fmpz_invmod(rop, op, fq_ctx_prime(ctx));
_fmpz_vec_zero(rop + 1, d - 1);
}
else
{
_fmpz_mod_poly_invmod(rop, op, len, ctx->modulus->coeffs, d + 1, ctx->ctxp);
}
}
void
fq_inv(fq_t rop, const fq_t op, const fq_ctx_t ctx)
{
if (fq_is_zero(op, ctx))
{
flint_throw(FLINT_ERROR, "Exception (fq_inv). Zero is not invertible.\n");
}
else
{
const slong d = fq_ctx_degree(ctx);
fmpz *t;
if (rop == op)
{
t = _fmpz_vec_init(d);
}
else
{
fmpz_poly_fit_length(rop, d);
t = rop->coeffs;
}
_fq_inv(t, op->coeffs, op->length, ctx);
if (rop == op)
{
_fmpz_vec_clear(rop->coeffs, rop->alloc);
rop->coeffs = t;
rop->alloc = d;
rop->length = d;
}
else
{
_fmpz_poly_set_length(rop, d);
}
_fmpz_poly_normalise(rop);
}
}