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/*
Copyright (C) 2010 William Hart
Copyright (C) 2012 Sebastian Pancratz
Copyright (C) 2012 Fredrik Johansson
This file is part of Arb.
Arb 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 <http://www.gnu.org/licenses/>.
*/
#include "acb_poly.h"
void
_acb_poly_compose_horner(acb_ptr res,
acb_srcptr poly1, slong len1,
acb_srcptr poly2, slong len2, slong prec)
{
if (len1 == 1)
{
acb_set(res, poly1);
}
else if (len2 == 1)
{
_acb_poly_evaluate(res, poly1, len1, poly2, prec);
}
else if (len1 == 2)
{
_acb_vec_scalar_mul(res, poly2, len2, poly1 + 1, prec);
acb_add(res, res, poly1, prec);
}
else
{
const slong alloc = (len1 - 1) * (len2 - 1) + 1;
slong i = len1 - 1, lenr = len2;
acb_ptr t, t1, t2;
t = _acb_vec_init(alloc);
if (len1 % 2 == 0)
{
t1 = res;
t2 = t;
}
else
{
t1 = t;
t2 = res;
}
/* Perform the first two steps as one,
"res = a(m) * poly2 + a(m-1)". */
{
_acb_vec_scalar_mul(t1, poly2, len2, poly1 + i, prec);
i--;
acb_add(t1 + 0, t1 + 0, poly1 + i, prec);
}
while (i--)
{
_acb_poly_mul(t2, t1, lenr, poly2, len2, prec);
lenr += len2 - 1;
{
void *t_ = t1;
t1 = t2;
t2 = t_;
}
acb_add(t1 + 0, t1 + 0, poly1 + i, prec);
}
_acb_vec_clear(t, alloc);
}
}
void acb_poly_compose_horner(acb_poly_t res,
const acb_poly_t poly1, const acb_poly_t poly2, slong prec)
{
const slong len1 = poly1->length;
const slong len2 = poly2->length;
if (len1 == 0)
{
acb_poly_zero(res);
}
else if (len1 == 1 || len2 == 0)
{
acb_poly_set_acb(res, poly1->coeffs);
}
else
{
const slong lenr = (len1 - 1) * (len2 - 1) + 1;
if (res != poly1 && res != poly2)
{
acb_poly_fit_length(res, lenr);
_acb_poly_compose_horner(res->coeffs, poly1->coeffs, len1,
poly2->coeffs, len2, prec);
}
else
{
acb_poly_t t;
acb_poly_init2(t, lenr);
_acb_poly_compose_horner(t->coeffs, poly1->coeffs, len1,
poly2->coeffs, len2, prec);
acb_poly_swap(res, t);
acb_poly_clear(t);
}
_acb_poly_set_length(res, lenr);
_acb_poly_normalise(res);
}
}
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