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

106 lines
3.0 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 "fq_nmod.h"
#include "nmod_mat.h"
/*
Computes the norm on $\mathbf{Q}_q$ to precision $N \geq 1$.
When $N = 1$, this computes the norm on $\mathbf{F}_q$.
*/
void _fq_nmod_norm(fmpz_t rop2, const mp_limb_t *op, slong len,
const fq_nmod_ctx_t ctx)
{
const slong d = fq_nmod_ctx_degree(ctx);
mp_limb_t rop;
if (len == 1)
{
rop = n_powmod2_ui_preinv(op[0], d, ctx->mod.n, ctx->mod.ninv);
}
else
{
/* Construct an ad hoc matrix M and set rop to det(M) */
{
const slong n = d + len - 1;
slong i, k;
nmod_mat_t M;
nmod_mat_init(M, n, n, ctx->mod.n);
for (k = 0; k < len-1; k++)
{
for (i = 0; i < ctx->len; i++)
{
M->entries[k * n + k + (d - ctx->j[i])] = ctx->a[i];
}
}
for (k = 0; k < d; k++)
{
for (i = 0; i < len; i++)
{
M->entries[(len-1 + k) * n + k + (len-1 - i)] = op[i];
}
}
rop = _nmod_mat_det(M);
nmod_mat_clear(M);
}
/*
XXX: This part of the code is currently untested as the Conway
polynomials used for the extension Fq/Fp are monic.
*/
if (ctx->a[ctx->len - 1] != WORD(1))
{
mp_limb_t f;
f = n_powmod2_ui_preinv(ctx->a[ctx->len - 1], len - 1, ctx->mod.n, ctx->mod.ninv);
f = n_invmod(f, ctx->mod.n);
rop = n_mulmod2_preinv(f, rop, ctx->mod.n, ctx->mod.ninv);
}
}
fmpz_set_ui(rop2, rop);
}
void fq_nmod_norm(fmpz_t rop, const fq_nmod_t op, const fq_nmod_ctx_t ctx)
{
if (fq_nmod_is_zero(op, ctx))
{
fmpz_zero(rop);
return;
}
else
{
_fq_nmod_norm(rop, op->coeffs, op->length, ctx);
}
}