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

98 lines
2.9 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
******************************************************************************/
#include "qadic.h"
/*
Forms the product of (op1,len1) and (op2,len2) modulo (a,j,lena) and pN.
Assumes that len1 >= len2 > 0. Requires rop to be of size at least
len1 + len2 - 1.
*/
static
void _qadic_mul(fmpz *rop,
const fmpz *op1, slong len1, const fmpz *op2, slong len2,
const fmpz *a, const slong *j, slong lena, const fmpz_t pN)
{
_fmpz_poly_mul(rop, op1, len1, op2, len2);
_fmpz_mod_poly_reduce(rop, len1 + len2 - 1, a, j, lena, pN);
}
void qadic_mul(qadic_t x, const qadic_t y, const qadic_t z,
const qadic_ctx_t ctx)
{
const slong leny = y->length;
const slong lenz = z->length;
const slong lenx = leny + lenz - 1;
const slong N = qadic_prec(x);
const slong d = qadic_ctx_degree(ctx);
if (leny == 0 || lenz == 0 || y->val + z->val >= N)
{
qadic_zero(x);
}
else
{
fmpz *t;
fmpz_t pN;
int alloc;
x->val = y->val + z->val;
alloc = _padic_ctx_pow_ui(pN, N - x->val, &ctx->pctx);
if (x == y || x == z)
{
t = _fmpz_vec_init(lenx);
}
else
{
padic_poly_fit_length(x, lenx);
t = x->coeffs;
}
if (leny >= lenz)
_qadic_mul(t, y->coeffs, leny,
z->coeffs, lenz, ctx->a, ctx->j, ctx->len, pN);
else
_qadic_mul(t, z->coeffs, lenz,
y->coeffs, leny, ctx->a, ctx->j, ctx->len, pN);
if (x == y || x == z)
{
_fmpz_vec_clear(x->coeffs, x->alloc);
x->coeffs = t;
x->alloc = lenx;
}
_padic_poly_set_length(x, FLINT_MIN(lenx, d));
_padic_poly_normalise(x);
if (alloc)
fmpz_clear(pN);
}
}