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/*
* Montgomery Reduction
* (C) 1999-2010 Jack Lloyd
* 2006 Luca Piccarreta
*
* Distributed under the terms of the Botan license
*/
#include <botan/internal/mp_core.h>
#include <botan/internal/mp_asm.h>
#include <botan/internal/mp_asmi.h>
#include <botan/mem_ops.h>
namespace Botan {
extern "C" {
/*
* Montgomery Reduction Algorithm
*/
void bigint_monty_redc(word z[], size_t z_size,
word ws[],
const word x[], size_t x_size,
word u)
{
const size_t blocks_of_8 = x_size - (x_size % 8);
for(size_t i = 0; i != x_size; ++i)
{
word* z_i = z + i;
const word y = z_i[0] * u;
/*
bigint_linmul3(ws, x, x_size, y);
bigint_add2(z_i, z_size - i, ws, x_size+1);
*/
word carry = 0;
for(size_t j = 0; j != blocks_of_8; j += 8)
carry = word8_madd3(z_i + j, x + j, y, carry);
for(size_t j = blocks_of_8; j != x_size; ++j)
z_i[j] = word_madd3(x[j], y, z_i[j], &carry);
word z_sum = z_i[x_size] + carry;
carry = (z_sum < z_i[x_size]);
z_i[x_size] = z_sum;
// Note: not constant time
for(size_t j = x_size + 1; carry && j != z_size - i; ++j)
{
++z_i[j];
carry = !z_i[j];
}
}
word borrow = 0;
for(size_t i = 0; i != x_size; ++i)
ws[i] = word_sub(z[x_size + i], x[i], &borrow);
ws[x_size] = word_sub(z[x_size+x_size], 0, &borrow);
copy_mem(ws + x_size + 1, z + x_size, x_size + 1);
copy_mem(z, ws + borrow*(x_size+1), x_size + 1);
clear_mem(z + x_size + 1, z_size - x_size - 1);
}
}
}
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