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/*
mul.c: polynomial multiplication
Copyright (C) 2007, 2008, David Harvey
This file is part of the zn_poly library (version 0.8).
This program 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) version 3 of the License.
This program 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 this program. If not, see <http://www.gnu.org/licenses/>.
*/
#include "zn_poly_internal.h"
ulong _zn_array_mul_get_fudge(size_t len1, size_t len2, int squaring,
const zn_mod_t mod)
{
ZNP_ASSERT(len2 >= 1);
ZNP_ASSERT(len1 >= len2);
if (!(mod->n & 1))
// no fudge if the modulus is even.
return 1;
tuning_info_t* i = &tuning_info[mod->bits];
if (!squaring)
{
if (len2 < i->mul_KS2_crossover || len2 < i->mul_KS4_crossover ||
len2 < i->mul_fft_crossover)
// fudge is -B
return mod->n - mod->B;
}
else
{
if (len2 < i->sqr_KS2_crossover || len2 < i->sqr_KS4_crossover ||
len2 < i->sqr_fft_crossover)
// fudge is -B
return mod->n - mod->B;
}
// return whatever fudge is used by the fft multiplication code
return zn_array_mul_fft_get_fudge(len1, len2, squaring, mod);
}
void _zn_array_mul(ulong* res, const ulong* op1, size_t len1,
const ulong* op2, size_t len2,
int fastred, const zn_mod_t mod)
{
ZNP_ASSERT(len2 >= 1);
ZNP_ASSERT(len1 >= len2);
// we can use REDC reduction if the modulus is odd and the caller is happy
// to receive the result with a fudge factor
int odd = (mod->n & 1);
int redc = fastred && odd;
if (len2 == 1)
{
// special case for 1xN multiplication
_zn_array_scalar_mul(res, op1, len1, op2[0], redc, mod);
return;
}
tuning_info_t* i = &tuning_info[mod->bits];
if (op1 != op2 || len1 != len2)
{
// multiplying two distinct inputs
if (len2 < i->mul_KS2_crossover)
zn_array_mul_KS1(res, op1, len1, op2, len2, redc, mod);
else if (len2 < i->mul_KS4_crossover)
zn_array_mul_KS2(res, op1, len1, op2, len2, redc, mod);
else if (!odd || len2 < i->mul_fft_crossover)
zn_array_mul_KS4(res, op1, len1, op2, len2, redc, mod);
else
{
ulong scale = fastred ? 1 :
zn_array_mul_fft_get_fudge(len1, len2, 0, mod);
zn_array_mul_fft(res, op1, len1, op2, len2, scale, mod);
}
}
else
{
// squaring a single input
if (len2 < i->sqr_KS2_crossover)
zn_array_mul_KS1(res, op1, len1, op2, len2, redc, mod);
else if (len2 < i->sqr_KS4_crossover)
zn_array_mul_KS2(res, op1, len1, op2, len2, redc, mod);
else if (!odd || len2 < i->sqr_fft_crossover)
zn_array_mul_KS4(res, op1, len1, op2, len2, redc, mod);
else
{
ulong scale = fastred ? 1 :
zn_array_mul_fft_get_fudge(len1, len2, 1, mod);
zn_array_mul_fft(res, op1, len1, op2, len2, 1, mod);
}
}
}
void zn_array_mul(ulong* res, const ulong* op1, size_t len1,
const ulong* op2, size_t len2, const zn_mod_t mod)
{
_zn_array_mul(res, op1, len1, op2, len2, 0, mod);
}
// end of file ****************************************************************
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