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/*
Copyright (C) 2010 Sebastian Pancratz
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"
void
_fmpz_poly_pow_binexp(fmpz * res, const fmpz * poly, slong len, ulong e)
{
ulong bit = ~((~UWORD(0)) >> 1);
slong rlen;
slong alloc = (slong) e * (len - 1) + 1;
fmpz *v = _fmpz_vec_init(alloc);
fmpz *R, *S, *T;
/*
Set bits to the bitmask with a 1 one place lower than the msb of e
*/
while ((bit & e) == UWORD(0))
bit >>= 1;
bit >>= 1;
/*
Trial run without any polynomial arithmetic to determine the parity
of the number of swaps; then set R and S accordingly
*/
{
unsigned int swaps = 0U;
ulong bit2 = bit;
if ((bit2 & e))
swaps = ~swaps;
while (bit2 >>= 1)
if ((bit2 & e) == UWORD(0))
swaps = ~swaps;
if (swaps == 0U)
{
R = res;
S = v;
}
else
{
R = v;
S = res;
}
}
/*
We unroll the first step of the loop, referring to {poly, len}
*/
_fmpz_poly_sqr(R, poly, len);
rlen = 2 * len - 1;
if ((bit & e))
{
_fmpz_poly_mul(S, R, rlen, poly, len);
rlen += len - 1;
T = R;
R = S;
S = T;
}
while ((bit >>= 1))
{
if ((bit & e))
{
_fmpz_poly_sqr(S, R, rlen);
rlen += rlen - 1;
_fmpz_poly_mul(R, S, rlen, poly, len);
rlen += len - 1;
}
else
{
_fmpz_poly_sqr(S, R, rlen);
rlen += rlen - 1;
T = R;
R = S;
S = T;
}
}
_fmpz_vec_clear(v, alloc);
}
void
fmpz_poly_pow_binexp(fmpz_poly_t res, const fmpz_poly_t poly, ulong e)
{
const slong len = poly->length;
slong rlen;
if ((len < 2) | (e < UWORD(3)))
{
if (e == UWORD(0))
fmpz_poly_set_ui(res, 1);
else if (len == 0)
fmpz_poly_zero(res);
else if (len == 1)
{
fmpz_poly_fit_length(res, 1);
fmpz_pow_ui(res->coeffs, poly->coeffs, e);
_fmpz_poly_set_length(res, 1);
}
else if (e == UWORD(1))
fmpz_poly_set(res, poly);
else /* e == UWORD(2) */
fmpz_poly_sqr(res, poly);
return;
}
rlen = (slong) e * (len - 1) + 1;
if (res != poly)
{
fmpz_poly_fit_length(res, rlen);
_fmpz_poly_pow_binexp(res->coeffs, poly->coeffs, len, e);
_fmpz_poly_set_length(res, rlen);
}
else
{
fmpz_poly_t t;
fmpz_poly_init2(t, rlen);
_fmpz_poly_pow_binexp(t->coeffs, poly->coeffs, len, e);
_fmpz_poly_set_length(t, rlen);
fmpz_poly_swap(res, t);
fmpz_poly_clear(t);
}
}