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/*
Copyright (C) 2023 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 "gr_vec.h"
#include "gr_poly.h"
/* todo: fmpz_poly has a better algorithm (assuming that generating
binomial coefficients is fast) */
int
_gr_poly_taylor_shift_divconquer(gr_ptr res, gr_srcptr poly, slong len, gr_srcptr c, gr_ctx_t ctx)
{
int status;
slong sz = ctx->sizeof_elem;
status = GR_SUCCESS;
if (res != poly)
status |= _gr_vec_set(res, poly, len, ctx);
if (len <= 1 || gr_is_zero(c, ctx) == T_TRUE)
return status;
if (len == 2)
return gr_addmul(res, GR_ENTRY(res, 1, sz), c, ctx);
{
gr_ptr t;
GR_TMP_INIT_VEC(t, 2, ctx);
status |= gr_set(t, c, ctx);
status |= gr_one(GR_ENTRY(t, 1, sz), ctx);
status |= _gr_poly_compose_divconquer(res, res, len, t, 2, ctx);
GR_TMP_CLEAR_VEC(t, 2, ctx);
return status;
}
}
int
gr_poly_taylor_shift_divconquer(gr_poly_t res, const gr_poly_t f, gr_srcptr c, gr_ctx_t ctx)
{
int status = GR_SUCCESS;
if (res != f)
status |= gr_poly_set(res, f, ctx);
status |= _gr_poly_taylor_shift_divconquer(res->coeffs, res->coeffs, res->length, c, ctx);
/* Normally the leading coefficient does not change, but it may have
exactified from maybe-zero to definitely-zero when working with
inexact represenations of the zero ring; it may also have been
mutated to a temporary value by an algorithm which fails with GR_UNABLE. */
_gr_poly_normalise(res, ctx);
return status;
}