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/**
* (C) Copyright Projet SECRET, INRIA, Rocquencourt
* (C) Bhaskar Biswas and Nicolas Sendrier
*
* (C) 2014 cryptosource GmbH
* (C) 2014 Falko Strenzke fstrenzke@cryptosource.de
*
* Botan is released under the Simplified BSD License (see license.txt)
*
*/
#include <botan/internal/binary_matrix.h>
namespace Botan {
binary_matrix::binary_matrix (u32bit rown, u32bit coln)
{
m_coln = coln;
m_rown = rown;
m_rwdcnt = (1 + (m_coln - 1) / BITS_PER_U32);
m_elem = std::vector<u32bit>(m_rown * m_rwdcnt);
}
void binary_matrix::row_xor(u32bit a, u32bit b)
{
u32bit i;
for(i=0;i<m_rwdcnt;i++)
{
m_elem[a*m_rwdcnt+i]^=m_elem[b*m_rwdcnt+i];
}
}
//the matrix is reduced from LSB...(from right)
secure_vector<int> binary_matrix::row_reduced_echelon_form()
{
u32bit i, failcnt, findrow, max=m_coln - 1;
secure_vector<int> perm(m_coln);
for(i=0;i<m_coln;i++)
{
perm[i]=i;//initialize permutation.
}
failcnt = 0;
for(i=0;i<m_rown;i++,max--)
{
findrow=0;
for(u32bit j=i;j<m_rown;j++)
{
if(coef(j,max))
{
if (i!=j)//not needed as ith row is 0 and jth row is 1.
row_xor(i,j);//xor to the row.(swap)?
findrow=1;
break;
}//largest value found (end if)
}
if(!findrow)//if no row with a 1 found then swap last column and the column with no 1 down.
{
perm[m_coln - m_rown - 1 - failcnt] = max;
failcnt++;
if (!max)
{
//CSEC_FREE_MEM_CHK_SET_NULL(*p_perm);
//CSEC_THR_RETURN();
perm.resize(0);
}
i--;
}
else
{
perm[i+m_coln - m_rown] = max;
for(u32bit j=i+1;j<m_rown;j++)//fill the column downwards with 0's
{
if(coef(j,(max)))
{
row_xor(j,i);//check the arg. order.
}
}
for(int j=i-1;j>=0;j--)//fill the column with 0's upwards too.
{
if(coef(j,(max)))
{
row_xor(j,i);
}
}
}
}//end for(i)
return perm;
}
} // end namespace Botan
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