pqc/external/flint-2.4.3/fq/frobenius.c
2014-05-24 23:16:06 +02:00

103 lines
2.6 KiB
C

/*=============================================================================
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) 2012 Sebastian Pancratz
Copyright (C) 2013 Mike Hansen
******************************************************************************/
#include "ulong_extras.h"
#include "fq.h"
/*
Sets (rop, 2d-1) to the image of (op, len) under the Frobenius operator
raised to the e-th power, assuming that neither op nor e are zero.
*/
void
_fq_frobenius(fmpz * rop, const fmpz * op, slong len, slong e, const fq_ctx_t ctx)
{
const slong d = fq_ctx_degree(ctx);
if (len == 1) /* op is in Fp, not just Fq */
{
_fmpz_vec_set(rop, op, len);
_fmpz_vec_zero(rop + len, (2 * d - 1) - len);
}
else
{
fmpz_t t;
fmpz_init(t);
fmpz_pow_ui(t, fq_ctx_prime(ctx), e);
_fq_pow(rop, op, len, t, ctx);
fmpz_clear(t);
}
}
void
fq_frobenius(fq_t rop, const fq_t op, slong e, const fq_ctx_t ctx)
{
const slong d = fq_ctx_degree(ctx);
e = e % d;
if (e < 0)
e += d;
if (fq_is_zero(op, ctx))
{
fq_zero(rop, ctx);
}
else if (e == 0)
{
fq_set(rop, op, ctx);
}
else
{
fmpz *t;
if (rop == op)
{
t = _fmpz_vec_init(2 * d - 1);
}
else
{
fmpz_poly_fit_length(rop, 2 * d - 1);
t = rop->coeffs;
}
_fq_frobenius(t, op->coeffs, op->length, e, ctx);
if (rop == op)
{
_fmpz_vec_clear(rop->coeffs, rop->alloc);
rop->coeffs = t;
rop->alloc = 2 * d - 1;
rop->length = d;
}
else
{
_fmpz_poly_set_length(rop, d);
}
_fmpz_poly_normalise(rop);
}
}