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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>
#include <assert.h>
#include <stdio.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)
{
for(u32bit j = 0; j != x_size; ++j)
{
word* z_j = z + j;
const word y = z_j[0] * u;
const u32bit blocks = x_size - (x_size % 8);
word carry = 0;
for(u32bit i = 0; i != blocks; i += 8)
carry = word8_madd3(z_j + i, x + i, y, carry);
for(u32bit i = blocks; 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];
}
}
#if 0
if(bigint_cmp(z + x_size, x_size + 1, x, x_size) >= 0)
bigint_sub2(z + x_size, x_size + 1, x, x_size);
#else
/*
s32bit bigint_cmp(const word x[], u32bit x_size,
const word y[], u32bit y_size)
{
if(x_size < y_size) { return (-bigint_cmp(y, y_size, x, x_size)); }
while(x_size > y_size)
{
if(x[x_size-1])
return 1;
x_size--;
}
for(u32bit j = x_size; j > 0; --j)
{
if(x[j-1] > y[j-1]) return 1;
if(x[j-1] < y[j-1]) return -1;
}
return 0;
}
*/
/*
if((x_size+1) < x_size) { return (-bigint_cmp(y, x_size, x, (x_size+1))); }
while((x_size+1) > x_size)
{
if(x[(x_size+1)-1])
return 1;
(x_size+1)--;
}
for(u32bit j = (x_size+1); j > 0; --j)
{
if(x[j-1] > y[j-1]) return 1;
if(x[j-1] < y[j-1]) return -1;
}
return 0;
->
//can't happen: if((x_size+1) < x_size) { return (-bigint_cmp(y, x_size, x, (x_size+1))); }
// always true: while((x_size+1) > x_size)
// {
if(x[x_size])
return do_sub();
//rewrite as x_size: (x_size+1)--;
}
for(u32bit j = x_size; j > 0; --j)
{
if(x[j-1] > y[j-1])
return do_sub();
if(x[j-1] < y[j-1])
return;
}
return do_sub();
->
cleanup:
if(x[x_size])
return do_sub();
for(u32bit j = x_size; j > 0; --j)
{
if(x[j-1] > y[j-1])
return do_sub();
if(x[j-1] < y[j-1])
return;
}
return do_sub();
-> arg rewrite
bigint_cmp(z + x_size, x_size + 1, x, x_size)
x = z + x_size
x_size = x_size + 1
y = x
y_size = x_size
^ !!!
if(z[x_size + x_size + 1])
return do_sub();
for(u32bit j = x_size; j > 0; --j)
{
if(z[x_size+j-1] > x[j-1])
return do_sub();
if(z[x_size+j-1] < x[j-1])
return;
}
return do_sub();
*/
word carry = 0;
const u32bit blocks = x_size - (x_size % 8);
if(z[x_size + x_size])
{
//assert((bigint_cmp(z + x_size, x_size + 1, x, x_size) > 0);
goto do_sub;
}
for(u32bit j = x_size; j > 0; --j)
{
if(z[x_size + j - 1] > x[j-1])
{
//assert((bigint_cmp(z + x_size, x_size + 1, x, x_size) > 0);
goto do_sub;
}
if(z[x_size + j - 1] < x[j-1])
{
//assert((bigint_cmp(z + x_size, x_size + 1, x, x_size) < 0);
goto done;
}
}
// default to subtraction (equal)
//assert(m(bigint_cmp(z + x_size, x_size + 1, x, x_size) == 0);
do_sub:
//bigint_sub2(z + x_size, x_size + 1, x, x_size);
for(u32bit j = 0; j != blocks; j += 8)
carry = word8_sub2(z + x_size + j, x + j, carry);
for(u32bit j = blocks; j != x_size; ++j)
z[x_size + j] = word_sub(z[x_size + j], x[j], &carry);
if(carry)
--z[x_size+x_size];
done:
return;
#endif
}
}
}
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