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/*
* MP Shift Algorithms
* (C) 1999-2007 Jack Lloyd
*
* Distributed under the terms of the Botan license
*/
#include <botan/internal/mp_core.h>
#include <botan/mem_ops.h>
namespace Botan {
extern "C" {
/*
* Single Operand Left Shift
*/
void bigint_shl1(word x[], size_t x_size, size_t word_shift, size_t bit_shift)
{
if(word_shift)
{
for(size_t j = 1; j != x_size + 1; ++j)
x[(x_size - j) + word_shift] = x[x_size - j];
clear_mem(x, word_shift);
}
if(bit_shift)
{
word carry = 0;
for(size_t j = word_shift; j != x_size + word_shift + 1; ++j)
{
word temp = x[j];
x[j] = (temp << bit_shift) | carry;
carry = (temp >> (MP_WORD_BITS - bit_shift));
}
}
}
/*
* Single Operand Right Shift
*/
void bigint_shr1(word x[], size_t x_size, size_t word_shift, size_t bit_shift)
{
if(x_size < word_shift)
{
clear_mem(x, x_size);
return;
}
if(word_shift)
{
copy_mem(x, x + word_shift, x_size - word_shift);
clear_mem(x + x_size - word_shift, word_shift);
}
if(bit_shift)
{
word carry = 0;
size_t top = x_size - word_shift;
while(top >= 4)
{
word w = x[top-1];
x[top-1] = (w >> bit_shift) | carry;
carry = (w << (MP_WORD_BITS - bit_shift));
w = x[top-2];
x[top-2] = (w >> bit_shift) | carry;
carry = (w << (MP_WORD_BITS - bit_shift));
w = x[top-3];
x[top-3] = (w >> bit_shift) | carry;
carry = (w << (MP_WORD_BITS - bit_shift));
w = x[top-4];
x[top-4] = (w >> bit_shift) | carry;
carry = (w << (MP_WORD_BITS - bit_shift));
top -= 4;
}
while(top)
{
word w = x[top-1];
x[top-1] = (w >> bit_shift) | carry;
carry = (w << (MP_WORD_BITS - bit_shift));
top--;
}
}
}
/*
* Two Operand Left Shift
*/
void bigint_shl2(word y[], const word x[], size_t x_size,
size_t word_shift, size_t bit_shift)
{
for(size_t j = 0; j != x_size; ++j)
y[j + word_shift] = x[j];
if(bit_shift)
{
word carry = 0;
for(size_t j = word_shift; j != x_size + word_shift + 1; ++j)
{
word w = y[j];
y[j] = (w << bit_shift) | carry;
carry = (w >> (MP_WORD_BITS - bit_shift));
}
}
}
/*
* Two Operand Right Shift
*/
void bigint_shr2(word y[], const word x[], size_t x_size,
size_t word_shift, size_t bit_shift)
{
if(x_size < word_shift) return;
for(size_t j = 0; j != x_size - word_shift; ++j)
y[j] = x[j + word_shift];
if(bit_shift)
{
word carry = 0;
for(size_t j = x_size - word_shift; j > 0; --j)
{
word w = y[j-1];
y[j-1] = (w >> bit_shift) | carry;
carry = (w << (MP_WORD_BITS - bit_shift));
}
}
}
}
}
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