pqc/external/flint-2.4.3/fq/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.h"
#include "fq_poly.h"
void
fq_ctx_init_modulus(fq_ctx_t ctx, fmpz_mod_poly_t modulus, const char *var)
{
slong nz;
int i, j;
fmpz* p;
fmpz_t inv;
p = &(modulus->p);
/* Count number of nonzero coefficients */
nz = 0;
for (i = 0; i < modulus->length; i++)
{
if (!fmpz_is_zero(modulus->coeffs + i))
{
nz += 1;
}
}
ctx->len = nz;
ctx->a = _fmpz_vec_init(ctx->len);
ctx->j = flint_malloc(ctx->len * sizeof(slong));
fmpz_init(inv);
fmpz_invmod(inv, modulus->coeffs + modulus->length - 1, p);
/* Copy the polynomial */
j = 0;
for (i = 0; i < modulus->length; i++)
{
if (!fmpz_is_zero(modulus->coeffs + i))
{
fmpz_mul(ctx->a + j, inv, modulus->coeffs + i);
fmpz_mod(ctx->a + j, ctx->a + j, p);
ctx->j[j] = i;
j++;
}
}
fmpz_clear(inv);
if (ctx->len < 6)
ctx->sparse_modulus = 1;
else
ctx->sparse_modulus = 0;
fmpz_init_set(fq_ctx_prime(ctx), p);
ctx->var = flint_malloc(strlen(var) + 1);
strcpy(ctx->var, var);
/* Set the modulus */
fmpz_mod_poly_init(ctx->modulus, fq_ctx_prime(ctx));
fmpz_mod_poly_set(ctx->modulus, modulus);
/* Precompute the inverse of the modulus */
fmpz_mod_poly_init(ctx->inv, fq_ctx_prime(ctx));
fmpz_mod_poly_reverse(ctx->inv, ctx->modulus, ctx->modulus->length);
fmpz_mod_poly_inv_series_newton(ctx->inv, ctx->inv, ctx->modulus->length);
}