pqc/external/flint-2.4.3/fq_nmod/ctx_init_modulus.c

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2014-05-18 22:03:37 +00:00
/*=============================================================================
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) 2013 Mike Hansen
******************************************************************************/
#include <stdio.h>
#include <string.h>
#include "fq_nmod.h"
void
fq_nmod_ctx_init_modulus(fq_nmod_ctx_t ctx, const nmod_poly_t modulus,
const char *var)
{
slong nz;
int i, j;
mp_limb_t inv;
fmpz_init(fq_nmod_ctx_prime(ctx));
fmpz_set_ui(fq_nmod_ctx_prime(ctx), modulus->mod.n);
ctx->mod.n = modulus->mod.n;
ctx->mod.ninv = modulus->mod.ninv;
ctx->mod.norm = modulus->mod.norm;
/* Count number of nonzero coefficients */
nz = 0;
for (i = 0; i < modulus->length; i++)
{
if (modulus->coeffs[i] != 0)
{
nz += 1;
}
}
ctx->len = nz;
ctx->a = _nmod_vec_init(ctx->len);
ctx->j = flint_malloc(ctx->len * sizeof(mp_limb_t));
inv = n_invmod(modulus->coeffs[modulus->length - 1], ctx->mod.n);
/* Copy the polynomial */
j = 0;
for (i = 0; i < modulus->length; i++)
{
if (modulus->coeffs[i] != 0)
{
ctx->a[j] = n_mulmod2_preinv(inv, modulus->coeffs[i],
ctx->mod.n, ctx->mod.ninv);
ctx->j[j] = i;
j++;
}
}
if (ctx->len < 6)
ctx->sparse_modulus = 1;
else
ctx->sparse_modulus = 0;
ctx->var = flint_malloc(strlen(var) + 1);
strcpy(ctx->var, var);
/* Set the modulus */
nmod_poly_init(ctx->modulus, ctx->mod.n);
nmod_poly_set(ctx->modulus, modulus);
/* Precompute the inverse of the modulus */
nmod_poly_init(ctx->inv, ctx->mod.n);
nmod_poly_reverse(ctx->inv, ctx->modulus, ctx->modulus->length);
nmod_poly_inv_series_newton(ctx->inv, ctx->inv, ctx->modulus->length);
}