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/*************************************************
* Montgomery Reduction Source File *
* (C) 1999-2008 Jack Lloyd *
* 2006 Luca Piccarreta *
*************************************************/
#include <botan/mp_core.h>
#include <botan/mp_asm.h>
#include <botan/mp_asmi.h>
namespace Botan {
extern "C" {
/*************************************************
* Montgomery Reduction Algorithm *
*************************************************/
void bigint_monty_redc(word z[], u32bit z_size,
const word x[], u32bit x_size, word u)
{
const u32bit blocks_of_8 = x_size - (x_size % 8);
for(u32bit j = 0; j != x_size; ++j)
{
word* z_j = z + j;
const word y = z_j[0] * u;
word carry = 0;
for(u32bit i = 0; i != blocks_of_8; i += 8)
carry = word8_madd3(z_j + i, x + i, y, carry);
for(u32bit i = blocks_of_8; i != x_size; ++i)
z_j[i] = word_madd3(x[i], y, z_j[i], &carry);
word z_sum = z_j[x_size] + carry;
carry = (z_sum < z_j[x_size]);
z_j[x_size] = z_sum;
for(u32bit k = x_size + 1; carry && k != z_size - j; ++k)
{
++z_j[k];
carry = !z_j[k];
}
}
// Check if z[x_size...x_size+1] >= x[0...x_size] using bigint_cmp (inlined)
if(!z[x_size + x_size])
{
for(u32bit j = x_size; j > 0; --j)
{
if(z[x_size + j - 1] > x[j-1])
break;
if(z[x_size + j - 1] < x[j-1])
return;
}
}
// If the compare above is true, subtract using bigint_sub2 (inlined)
word carry = 0;
for(u32bit j = 0; j != blocks_of_8; j += 8)
carry = word8_sub2(z + x_size + j, x + j, carry);
for(u32bit j = blocks_of_8; j != x_size; ++j)
z[x_size + j] = word_sub(z[x_size + j], x[j], &carry);
if(carry)
--z[x_size+x_size];
}
}
}
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