malb / M4RI (http://m4ri.sagemath.org/)

M4RI is a library for fast arithmetic with dense matrices over F2. It was started by Gregory Bard, is maintained by Martin Albrecht. Several people contributed to it. The name M4RI comes from the first implemented algorithm: The "Method of the Four Russians" inversion algorithm published by Gregory Bard. This algorithm in turn is named after the "Method of the Four Russians" multiplication algorithm which is probably better referred to as Kronrod's method. M4RI is used by the Sage mathematics software and the PolyBoRi library. M4RI is available under the General Public License Version 2 or later (GPLv2+).

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commit 221: 378b655e4717
parent 220: 2ed374681d29
branch: default
use fast pivot searching code in mzd_reduce_m4ri
Martin Albrecht / malb
14 months ago
M4RI / src / brilliantrussian.c
r221:378b655e4717 1278 loc 40.6 KB embed / history / annotate / raw /
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/*******************************************************************
*
*                 M4RI: Linear Algebra over GF(2)
*
*    Copyright (C) 2007, 2008 Gregory Bard <bard@fordham.edu>
*    Copyright (C) 2008 Martin Albrecht <M.R.Albrecht@rhul.ac.uk>
*
*  Distributed under the terms of the GNU General Public License (GPL) 
*  version 2 or higher.
*
*    This code is distributed in the hope that it will be useful,
*    but WITHOUT ANY WARRANTY; without even the implied warranty of
*    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
*    General Public License for more details.
*
*  The full text of the GPL is available at:
*
*                  http://www.gnu.org/licenses/
*
********************************************************************/

#include "misc.h"

#ifdef HAVE_SSE2
#include <emmintrin.h>
#endif

#include <assert.h>

#include "brilliantrussian.h"
#include "grayflex.h"


/**
 * \brief Perform Gaussian reduction to reduced row echelon form on a
 * submatrix.
 * 
 * The submatrix has dimension at most k starting at r x c of A. Checks
 * for pivot rows up to row endrow (exclusive). Terminates as soon as
 * finding a pivot column fails.
 *
 * \param A Matrix.
 * \param r First row.
 * \param c First column.
 * \param k Maximal dimension of identity matrix to produce.
 * \param end_row Maximal row index (exclusive) for rows to consider
 * for inclusion.
 */

static inline int _mzd_gauss_submatrix_full(packedmatrix *A, size_t r, size_t c, size_t end_row, int k) {
  size_t i,j,l;
  size_t start_row = r;
  int found;
  for (j=c; j<c+k; j++) {
    found = 0;
    for (i=start_row; i< end_row; i++) {
      /* first we need to clear the first columns */
      if(mzd_read_bits(A,i,c,j-c))
        for (l=0; l<j-c; l++)
          if (mzd_read_bit(A, i, c+l))
            mzd_row_add_offset(A, i, r+l, c+l);
      
      /* pivot? */
      if (mzd_read_bit(A, i, j)) {
        mzd_row_swap(A, i, start_row);
        /* clear above */
        for (l=r; l<start_row; l++) {
          if (mzd_read_bit(A, l, j)) {
            mzd_row_add_offset(A, l, start_row, j);
          }
        }
        start_row++;
        found = 1;
        break;
      }
    }
    if (found==0) {
      return j - c;
    }
  }
  return j - c;
}

/**
 * \brief Perform Gaussian reduction to upper triangular matrix on a
 * submatrix.
 * 
 * The submatrix has dimension at most k starting at r x c of A. Checks
 * for pivot rows up to row end_row (exclusive). Terminates as soon as
 * finding a pivot column fails.
 *
 * \param A Matrix.
 * \param r First row.
 * \param c First column.
 * \param k Maximal dimension of identity matrix to produce.
 * \param end_row Maximal row index (exclusive) for rows to consider
 * for inclusion.
 */

static inline int _mzd_gauss_submatrix(packedmatrix *A, size_t r, size_t c, size_t end_row, int k) {
  size_t i,j,l;
  size_t start_row = r;
  int found;
  for (j=c; j<c+k; j++) {
    found = 0;
    for (i=start_row; i< end_row; i++) {
      /* first we need to clear the first columns */
      for (l=0; l<j-c; l++)
        if (mzd_read_bit(A, i, c+l))
          mzd_row_add_offset(A, i, r+l, c+l);
      
      /* pivot? */
      if (mzd_read_bit(A, i, j)) {
        mzd_row_swap(A, i, start_row);
        start_row++;
        found = 1;
        break;
      }
    }
    if (found==0) {
      return j - c;
    }
  }
  return j - c;
}

/**
 * \brief Given a submatrix in upper triangular form compute the
 * reduced row echelon form.
 * 
 * The submatrix has dimension at most k starting at r x c of A. Checks
 * for pivot rows up to row end_row (exclusive). Terminates as soon as
 * finding a pivot column fails.
 *
 * \param A Matrix.
 * \param r First row.
 * \param c First column.
 * \param k Maximal dimension of identity matrix to produce.
 * \param end_row Maximal row index (exclusive) for rows to consider
 * for inclusion.
 */

static inline int _mzd_gauss_submatrix_top(packedmatrix *A, size_t r, size_t c, int k) {
  size_t j,l;
  size_t start_row = r;
  for (j=c; j<c+k; j++) {
    for (l=r; l<start_row; l++) {
      if (mzd_read_bit(A, l, j)) {
        mzd_row_add_offset(A, l, start_row, j);
      }
    }
    start_row++;
  }
  return k;
}

static inline void _mzd_copy_back_rows(packedmatrix *A, packedmatrix *U, size_t r, size_t c, size_t k) {
  size_t startblock = c/RADIX;
  size_t width = A->width - startblock;
  size_t i, j;
  for (i=0 ; i < k ; i++) {
    const word * const src = U->values + U->rowswap[i] + startblock;
    word *const dst = A->values + A->rowswap[r+i] + startblock;
    for (j=0; j< width; j++) {
      dst[j] = src[j];
    }
  }
}

void mzd_make_table( packedmatrix *M, size_t r, size_t c, int k, packedmatrix *T, size_t *L) {
  const size_t homeblock= c/RADIX;
  size_t i, j, rowneeded, id;
  size_t twokay= TWOPOW(k);
  size_t wide = T->width - homeblock;

  word *ti, *ti1, *m;

  ti1 = T->values + homeblock;
  ti = ti1 + T->width;
#ifdef HAVE_SSE2
  unsigned long incw = 0;
  if (T->width & 1) incw = 1;
  ti += incw;
#endif

  L[0]=0;
  for (i=1; i<twokay; i++) {
    rowneeded = r + codebook[k]->inc[i-1];
    id = codebook[k]->ord[i];
    L[id] = i;
    if (rowneeded >= M->nrows) {
      for (j = 0; j < wide; j++) {
        *ti++ = *ti1++;
      }
#ifdef HAVE_SSE2
      ti+=incw; ti1+=incw;
#endif
    } else {
      m = M->values + M->rowswap[rowneeded] + homeblock;

      /* Duff's device loop unrolling */
      register int n = (wide + 7) / 8;
      switch (wide % 8) {
      case 0: do { *(ti++) = *(m++) ^ *(ti1++);
      case 7:      *(ti++) = *(m++) ^ *(ti1++);
      case 6:      *(ti++) = *(m++) ^ *(ti1++);
      case 5:      *(ti++) = *(m++) ^ *(ti1++);
      case 4:      *(ti++) = *(m++) ^ *(ti1++);
      case 3:      *(ti++) = *(m++) ^ *(ti1++);
      case 2:      *(ti++) = *(m++) ^ *(ti1++);
      case 1:      *(ti++) = *(m++) ^ *(ti1++);
        } while (--n > 0);
      }
#ifdef HAVE_SSE2
      ti+=incw; ti1+=incw;
#endif
      ti += homeblock;
      ti1 += homeblock;
    }
  }
}

void mzd_process_rows(packedmatrix *M, size_t startrow, size_t stoprow, size_t startcol, int k, packedmatrix *T, size_t *L) {
  size_t r;
  const size_t blocknum=startcol/RADIX;
  size_t wide = M->width - blocknum;

  if(k==1) {
    word bm = ONE << ((RADIX - startcol - 1) % RADIX);

    for (r=startrow; r+2<=stoprow; r+=2) {
      word *t = T->values + T->rowswap[1] + blocknum;
      word *m0 = M->values + M->rowswap[r+0] + blocknum;
      word *m1 = M->values + M->rowswap[r+1] + blocknum;
      register int n = (wide + 7) / 8;

      if(*m0 & bm) {
        if(*m1 & bm) {
          switch (wide % 8) {
          case 0: do { *m0++ ^= *t; *m1++ ^= *t++;
          case 7:    *m0++ ^= *t; *m1++ ^= *t++;
          case 6:    *m0++ ^= *t; *m1++ ^= *t++;
          case 5:    *m0++ ^= *t; *m1++ ^= *t++;
          case 4:    *m0++ ^= *t; *m1++ ^= *t++;
          case 3:    *m0++ ^= *t; *m1++ ^= *t++;
          case 2:    *m0++ ^= *t; *m1++ ^= *t++;
          case 1:    *m0++ ^= *t; *m1++ ^= *t++;
            } while (--n > 0);
          }
        } else {
          switch (wide % 8) {
          case 0: do { *m0++ ^= *t++;
          case 7:    *m0++ ^= *t++;
          case 6:    *m0++ ^= *t++;
          case 5:    *m0++ ^= *t++;
          case 4:    *m0++ ^= *t++;
          case 3:    *m0++ ^= *t++;
          case 2:    *m0++ ^= *t++;
          case 1:    *m0++ ^= *t++;
            } while (--n > 0);
          }
        }
      } else if(*m1 & bm) {
          switch (wide % 8) {
          case 0: do { *m1++ ^= *t++;
          case 7:    *m1++ ^= *t++;
          case 6:    *m1++ ^= *t++;
          case 5:    *m1++ ^= *t++;
          case 4:    *m1++ ^= *t++;
          case 3:    *m1++ ^= *t++;
          case 2:    *m1++ ^= *t++;
          case 1:    *m1++ ^= *t++;
            } while (--n > 0);
          }
      }
    }

    for( ; r<stoprow; r++) {
      const int x0 = L[ (int)mzd_read_bits(M, r, startcol, k) ];
      word *m0 = M->values + M->rowswap[r] + blocknum;
      word *t0 = T->values + T->rowswap[x0] + blocknum;
      
      register int n = (wide + 7) / 8;
      switch (wide % 8) {
      case 0: do { *m0++ ^= *t0++;
        case 7:    *m0++ ^= *t0++;
        case 6:    *m0++ ^= *t0++;
        case 5:    *m0++ ^= *t0++;
        case 4:    *m0++ ^= *t0++;
        case 3:    *m0++ ^= *t0++;
        case 2:    *m0++ ^= *t0++;
        case 1:    *m0++ ^= *t0++;
        } while (--n > 0);
      }
    }
    return;
  }

  for (r=startrow; r+2<=stoprow; r+=2) {
    const int x0 = L[ (int)mzd_read_bits(M, r+0, startcol, k) ];
    const int x1 = L[ (int)mzd_read_bits(M, r+1, startcol, k) ];
    
    word *m0 = M->values + M->rowswap[r+0] + blocknum;
    word *t0 = T->values + T->rowswap[x0] + blocknum;

    word *m1 = M->values + M->rowswap[r+1] + blocknum;
    word *t1 = T->values + T->rowswap[x1] + blocknum;

    register int n = (wide + 7) / 8;
    switch (wide % 8) {
    case 0: do { *m0++ ^= *t0++; *m1++ ^= *t1++;
      case 7:    *m0++ ^= *t0++; *m1++ ^= *t1++;
      case 6:    *m0++ ^= *t0++; *m1++ ^= *t1++;
      case 5:    *m0++ ^= *t0++; *m1++ ^= *t1++;
      case 4:    *m0++ ^= *t0++; *m1++ ^= *t1++;
      case 3:    *m0++ ^= *t0++; *m1++ ^= *t1++;
      case 2:    *m0++ ^= *t0++; *m1++ ^= *t1++;
      case 1:    *m0++ ^= *t0++; *m1++ ^= *t1++;
      } while (--n > 0);
    }
  }

  for( ; r<stoprow; r++) {
    const int x0 = L[ (int)mzd_read_bits(M, r, startcol, k) ];
    word *m0 = M->values + M->rowswap[r] + blocknum;
    word *t0 = T->values + T->rowswap[x0] + blocknum;

    register int n = (wide + 7) / 8;
    switch (wide % 8) {
    case 0: do { *m0++ ^= *t0++;
      case 7:    *m0++ ^= *t0++;
      case 6:    *m0++ ^= *t0++;
      case 5:    *m0++ ^= *t0++;
      case 4:    *m0++ ^= *t0++;
      case 3:    *m0++ ^= *t0++;
      case 2:    *m0++ ^= *t0++;
      case 1:    *m0++ ^= *t0++;
      } while (--n > 0);
    }
  }
}

void mzd_process_rows2(packedmatrix *M, size_t startrow, size_t stoprow, size_t startcol, int k, packedmatrix *T0, size_t *L0, packedmatrix *T1, size_t *L1) {
  size_t r;
  const size_t blocknum=startcol/RADIX;
  const size_t wide = M->width - blocknum;

  const int ka = k/2;
  const int kb = k-k/2;

#ifdef HAVE_OPENMP
#pragma omp parallel for private(r) shared(startrow, stoprow) schedule(dynamic,32) if(stoprow-startrow > 128)
#endif
  for(r=startrow; r<stoprow; r++) {
    const int x0 = L0[ (int)mzd_read_bits(M, r, startcol, ka)];
    const int x1 = L1[ (int)mzd_read_bits(M, r, startcol+ka, kb)];
    if(x0 == 0 && x1 == 0)
      continue;
    word * m0 = M->values + M->rowswap[r] + blocknum;
    const word *t0 = T0->values + T0->rowswap[x0] + blocknum;
    const word *t1 = T1->values + T1->rowswap[x1] + blocknum;

    register int n = (wide + 7) / 8;
    switch (wide % 8) {
    case 0: do { *m0++ ^= *t0++ ^ *t1++;
      case 7:    *m0++ ^= *t0++ ^ *t1++;
      case 6:    *m0++ ^= *t0++ ^ *t1++;
      case 5:    *m0++ ^= *t0++ ^ *t1++;
      case 4:    *m0++ ^= *t0++ ^ *t1++;
      case 3:    *m0++ ^= *t0++ ^ *t1++;
      case 2:    *m0++ ^= *t0++ ^ *t1++;
      case 1:    *m0++ ^= *t0++ ^ *t1++;
      } while (--n > 0);
    }
  }
}

void mzd_process_rows3(packedmatrix *M, size_t startrow, size_t stoprow, size_t startcol, int k, packedmatrix *T0, size_t *L0, packedmatrix *T1, size_t *L1, packedmatrix *T2, size_t *L2) {
  size_t r;
  const size_t blocknum=startcol/RADIX;
  const size_t wide = M->width - blocknum;

  int rem = k%3;
  
  const int ka = k/3 + ((rem>=2) ? 1 : 0);
  const int kb = k/3 + ((rem>=1) ? 1 : 0);
  const int kc = k/3;

#ifdef HAVE_OPENMP
#pragma omp parallel for private(r) shared(startrow, stoprow) schedule(dynamic,32) if(stoprow-startrow > 128)
#endif
  for(r=startrow; r<stoprow; r++) {
    const int x0 = L0[ (int)mzd_read_bits(M, r, startcol, ka)];
    const int x1 = L1[ (int)mzd_read_bits(M, r, startcol+ka, kb)];
    const int x2 = L2[ (int)mzd_read_bits(M, r, startcol+ka+kb, kc)];
    if(x0 == 0 && x1 == 0 && x2 == 0) 
      continue;

    word * m0 = M->values + M->rowswap[r] + blocknum;
    const word *t0 = T0->values + T0->rowswap[x0] + blocknum;
    const word *t1 = T1->values + T1->rowswap[x1] + blocknum;
    const word *t2 = T2->values + T2->rowswap[x2] + blocknum;

    register int n = (wide + 7) / 8;
    switch (wide % 8) {
    case 0: do { *m0++ ^= *t0++ ^ *t1++ ^ *t2++;
      case 7:    *m0++ ^= *t0++ ^ *t1++ ^ *t2++;
      case 6:    *m0++ ^= *t0++ ^ *t1++ ^ *t2++;
      case 5:    *m0++ ^= *t0++ ^ *t1++ ^ *t2++;
      case 4:    *m0++ ^= *t0++ ^ *t1++ ^ *t2++;
      case 3:    *m0++ ^= *t0++ ^ *t1++ ^ *t2++;
      case 2:    *m0++ ^= *t0++ ^ *t1++ ^ *t2++;
      case 1:    *m0++ ^= *t0++ ^ *t1++ ^ *t2++;
      } while (--n > 0);
    }
  }
}

void mzd_process_rows4(packedmatrix *M, size_t startrow, size_t stoprow, size_t startcol, int k, 
                       packedmatrix *T0, size_t *L0, packedmatrix *T1, size_t *L1, packedmatrix *T2, size_t *L2, packedmatrix *T3, size_t *L3) {
  size_t r;
  const size_t blocknum=startcol/RADIX;
  const size_t wide = M->width - blocknum;

  int rem = k%4;
  
  const int ka = k/4 + ((rem>=3) ? 1 : 0);
  const int kb = k/4 + ((rem>=2) ? 1 : 0);
  const int kc = k/4 + ((rem>=1) ? 1 : 0);
  const int kd = k/4;

#ifdef HAVE_OPENMP
#pragma omp parallel for private(r) shared(startrow, stoprow) schedule(dynamic,32) if(stoprow-startrow > 128)
#endif
  for(r=startrow; r<stoprow; r++) {
    const int x0 = L0[ (int)mzd_read_bits(M, r, startcol, ka)];
    const int x1 = L1[ (int)mzd_read_bits(M, r, startcol+ka, kb)];
    const int x2 = L2[ (int)mzd_read_bits(M, r, startcol+ka+kb, kc)];
    const int x3 = L3[ (int)mzd_read_bits(M, r, startcol+ka+kb+kc, kd)];
    if(x0 == 0 && x1 == 0 && x2 == 0 && x3 == 0) 
      continue;

    word * m0 = M->values + M->rowswap[r] + blocknum;
    const word *t0 = T0->values + T0->rowswap[x0] + blocknum;
    const word *t1 = T1->values + T1->rowswap[x1] + blocknum;
    const word *t2 = T2->values + T2->rowswap[x2] + blocknum;
    const word *t3 = T3->values + T3->rowswap[x3] + blocknum;
    
    register int n = (wide + 7) / 8;
    switch (wide % 8) {
    case 0: do { *m0++ ^= *t0++ ^ *t1++ ^ *t2++ ^ *t3++;
      case 7:    *m0++ ^= *t0++ ^ *t1++ ^ *t2++ ^ *t3++;
      case 6:    *m0++ ^= *t0++ ^ *t1++ ^ *t2++ ^ *t3++;
      case 5:    *m0++ ^= *t0++ ^ *t1++ ^ *t2++ ^ *t3++;
      case 4:    *m0++ ^= *t0++ ^ *t1++ ^ *t2++ ^ *t3++;
      case 3:    *m0++ ^= *t0++ ^ *t1++ ^ *t2++ ^ *t3++;
      case 2:    *m0++ ^= *t0++ ^ *t1++ ^ *t2++ ^ *t3++;
      case 1:    *m0++ ^= *t0++ ^ *t1++ ^ *t2++ ^ *t3++;
      } while (--n > 0);
    }
  }
}

void mzd_process_rows5(packedmatrix *M, size_t startrow, size_t stoprow, size_t startcol, int k, 
                       packedmatrix *T0, size_t *L0, packedmatrix *T1, size_t *L1, packedmatrix *T2, size_t *L2, packedmatrix *T3, size_t *L3,
                       packedmatrix *T4, size_t *L4) {
  size_t r;
  const size_t blocknum=startcol/RADIX;
  const size_t wide = M->width - blocknum;
  int rem = k%5;
  
  const int ka = k/5 + ((rem>=4) ? 1 : 0);
  const int kb = k/5 + ((rem>=3) ? 1 : 0);
  const int kc = k/5 + ((rem>=2) ? 1 : 0);
  const int kd = k/5 + ((rem>=1) ? 1 : 0);
  const int ke = k/5;

#ifdef HAVE_OPENMP
#pragma omp parallel for private(r) shared(startrow, stoprow) schedule(dynamic,32) if(stoprow-startrow > 128)
#endif
  for(r=startrow; r<stoprow; r++) {
    
    const int x0 = L0[ (int)mzd_read_bits(M, r, startcol, ka)];
    const int x1 = L1[ (int)mzd_read_bits(M, r, startcol+ka, kb)];
    const int x2 = L2[ (int)mzd_read_bits(M, r, startcol+ka+kb, kc)];
    const int x3 = L3[ (int)mzd_read_bits(M, r, startcol+ka+kb+kc, kd)];
    const int x4 = L4[ (int)mzd_read_bits(M, r, startcol+ka+kb+kc+kd, ke)];

    if(x0 == 0 && x1 == 0 && x2 == 0 && x3 == 0 && x4 == 0) 
      continue;

    word * m0 = M->values + M->rowswap[r] + blocknum;
    const word *t0 = T0->values + T0->rowswap[x0] + blocknum;
    const word *t1 = T1->values + T1->rowswap[x1] + blocknum;
    const word *t2 = T2->values + T2->rowswap[x2] + blocknum;
    const word *t3 = T3->values + T3->rowswap[x3] + blocknum;
    const word *t4 = T4->values + T4->rowswap[x4] + blocknum;
    
    register int n = (wide + 7) / 8;
    switch (wide % 8) {
    case 0: do { *m0++ ^= *t0++ ^ *t1++ ^ *t2++ ^ *t3++ ^ *t4++;
      case 7:    *m0++ ^= *t0++ ^ *t1++ ^ *t2++ ^ *t3++ ^ *t4++;
      case 6:    *m0++ ^= *t0++ ^ *t1++ ^ *t2++ ^ *t3++ ^ *t4++;
      case 5:    *m0++ ^= *t0++ ^ *t1++ ^ *t2++ ^ *t3++ ^ *t4++;
      case 4:    *m0++ ^= *t0++ ^ *t1++ ^ *t2++ ^ *t3++ ^ *t4++;
      case 3:    *m0++ ^= *t0++ ^ *t1++ ^ *t2++ ^ *t3++ ^ *t4++;
      case 2:    *m0++ ^= *t0++ ^ *t1++ ^ *t2++ ^ *t3++ ^ *t4++;
      case 1:    *m0++ ^= *t0++ ^ *t1++ ^ *t2++ ^ *t3++ ^ *t4++;
      } while (--n > 0);
    }
  }
}

void mzd_process_rows6(packedmatrix *M, size_t startrow, size_t stoprow, size_t startcol, int k, 
                       packedmatrix *T0, size_t *L0, packedmatrix *T1, size_t *L1, packedmatrix *T2, size_t *L2, packedmatrix *T3, size_t *L3,
                       packedmatrix *T4, size_t *L4, packedmatrix *T5, size_t *L5) {
  size_t r;
  const size_t blocknum=startcol/RADIX;
  const size_t wide = M->width - blocknum;

  int rem = k%6;
  
  const int ka = k/6 + ((rem>=5) ? 1 : 0);
  const int kb = k/6 + ((rem>=4) ? 1 : 0);
  const int kc = k/6 + ((rem>=3) ? 1 : 0);
  const int kd = k/6 + ((rem>=2) ? 1 : 0);
  const int ke = k/6 + ((rem>=1) ? 1 : 0);;
  const int kf = k/6;

#ifdef HAVE_OPENMP
#pragma omp parallel for private(r) shared(startrow, stoprow) schedule(dynamic,32) if(stoprow-startrow > 128)
#endif
  for(r=startrow; r<stoprow; r++) {
    const int x0 = L0[ (int)mzd_read_bits(M, r, startcol, ka)];
    const int x1 = L1[ (int)mzd_read_bits(M, r, startcol+ka, kb)];
    const int x2 = L2[ (int)mzd_read_bits(M, r, startcol+ka+kb, kc)];
    const int x3 = L3[ (int)mzd_read_bits(M, r, startcol+ka+kb+kc, kd)];
    const int x4 = L4[ (int)mzd_read_bits(M, r, startcol+ka+kb+kc+kd, ke)];
    const int x5 = L5[ (int)mzd_read_bits(M, r, startcol+ka+kb+kc+kd+ke, kf)];
    
    if(x0 == 0 && x1 == 0 && x2 == 0 && x3 == 0 && x4 == 0 && x5 == 0) 
      continue;

    word * m0 = M->values + M->rowswap[r] + blocknum;
    const word *t0 = T0->values + T0->rowswap[x0] + blocknum;
    const word *t1 = T1->values + T1->rowswap[x1] + blocknum;
    const word *t2 = T2->values + T2->rowswap[x2] + blocknum;
    const word *t3 = T3->values + T3->rowswap[x3] + blocknum;
    const word *t4 = T4->values + T4->rowswap[x4] + blocknum;
    const word *t5 = T5->values + T5->rowswap[x5] + blocknum;

    register int n = (wide + 7) / 8;
    switch (wide % 8) {
      case 0: do { *m0++ ^= *t0++ ^ *t1++ ^ *t2++ ^ *t3++ ^ *t4++ ^ *t5++;
      case 7:    *m0++ ^= *t0++ ^ *t1++ ^ *t2++ ^ *t3++ ^ *t4++ ^ *t5++;
      case 6:    *m0++ ^= *t0++ ^ *t1++ ^ *t2++ ^ *t3++ ^ *t4++ ^ *t5++;
      case 5:    *m0++ ^= *t0++ ^ *t1++ ^ *t2++ ^ *t3++ ^ *t4++ ^ *t5++;
      case 4:    *m0++ ^= *t0++ ^ *t1++ ^ *t2++ ^ *t3++ ^ *t4++ ^ *t5++;
      case 3:    *m0++ ^= *t0++ ^ *t1++ ^ *t2++ ^ *t3++ ^ *t4++ ^ *t5++;
      case 2:    *m0++ ^= *t0++ ^ *t1++ ^ *t2++ ^ *t3++ ^ *t4++ ^ *t5++;
      case 1:    *m0++ ^= *t0++ ^ *t1++ ^ *t2++ ^ *t3++ ^ *t4++ ^ *t5++;
      } while (--n > 0);
    }
  }
}

int mzd_reduce_m4ri(packedmatrix *A, int full, int k, packedmatrix *T, size_t *L) {
  /**
   * The algorithm works as follows:
   *
   * Step 1.Denote the first column to be processed in a given
   * iteration as \f$a_i\f$. Then, perform Gaussian elimination on the
   * first \f$3k\f$ rows after and including the \f$i\f$-th row to
   * produce an identity matrix in \f$a_{i,i} ... a_{i+k-1,i+k-1},\f$
   * and zeroes in \f$a_{i+k,i} ... a_{i+3k-1,i+k-1}\f$.
   *
   * Step 2. Construct a table consisting of the \f$2^k\f$ binary strings of
   * length k in a Gray code.  Thus with only \f$2^k\f$ vector
   * additions, all possible linear combinations of these k rows
   * have been precomputed.
   *
   *
   * Step 3. One can rapidly process the remaining rows from \f$i +
   * 3k\f$ until row \f$m\f$ (the last row) by using the table. For
   * example, suppose the \f$j\f$-th row has entries \f$a_{j,i}
   * ... a_{j,i+k-1}\f$ in the columns being processed. Selecting the
   * row of the table associated with this k-bit string, and adding it
   * to row j will force the k columns to zero, and adjust the
   * remaining columns from \f$ i + k\f$ to n in the appropriate way,
   * as if Gaussian elimination had been performed.
   *
   * Step 4. While the above form of the algorithm will reduce a
   * system of boolean linear equations to unit upper triangular form,
   * and thus permit a system to be solved with back substitution, the
   * M4RI algorithm can also be used to invert a matrix, or put the
   * system into reduced row echelon form (RREF). Simply run Step 3
   * on rows \f$0 ... i-1\f$ as well as on rows \f$i + 3k
   * ... m\f$. This only affects the complexity slightly, changing the
   * 2.5 coeffcient to 3
   */

  const size_t ncols = A->ncols; 
  size_t r = 0;
  size_t c = 0;
  int kbar = 0;

  if (k == 0) {
    k = m4ri_opt_k(A->nrows, A->ncols, 0);
    if (k>=7)
      k = 7;
    if ( (6*(1<<k)*A->ncols / 8.0) > CPU_L2_CACHE / 2.0 )
      k -= 1;
  }
  /*printf("k: %d\n",k);*/
  int kk = 6*k;

  packedmatrix *U  = mzd_init(kk, A->ncols);
  packedmatrix *T0 = mzd_init(TWOPOW(k), A->ncols);
  packedmatrix *T1 = mzd_init(TWOPOW(k), A->ncols);
  packedmatrix *T2 = mzd_init(TWOPOW(k), A->ncols);
  packedmatrix *T3 = mzd_init(TWOPOW(k), A->ncols);
  packedmatrix *T4 = mzd_init(TWOPOW(k), A->ncols);
  packedmatrix *T5 = mzd_init(TWOPOW(k), A->ncols);
  size_t *L0 = (size_t *)m4ri_mm_calloc(TWOPOW(k), sizeof(size_t));
  size_t *L1 = (size_t *)m4ri_mm_calloc(TWOPOW(k), sizeof(size_t));
  size_t *L2 = (size_t *)m4ri_mm_calloc(TWOPOW(k), sizeof(size_t));
  size_t *L3 = (size_t *)m4ri_mm_calloc(TWOPOW(k), sizeof(size_t));
  size_t *L4 = (size_t *)m4ri_mm_calloc(TWOPOW(k), sizeof(size_t));
  size_t *L5 = (size_t *)m4ri_mm_calloc(TWOPOW(k), sizeof(size_t));

  while(c<ncols) {
    if(c+kk > A->ncols) {
      kk = ncols - c;
    }
    if (full) {
      kbar = _mzd_gauss_submatrix_full(A, r, c, A->nrows, kk);
    } else {
      kbar = _mzd_gauss_submatrix(A, r, c, A->nrows, kk);
      /* this isn't necessary, adapt make_table */
      U = mzd_submatrix(U, A, r, 0, r+kbar, A->ncols);
      _mzd_gauss_submatrix_top(A, r, c, kbar);
    }

    if (kbar>5*k) {
      const int rem = kbar%6;
      const int ka = kbar/6 + ((rem>=5) ? 1 : 0);
      const int kb = kbar/6 + ((rem>=4) ? 1 : 0);
      const int kc = kbar/6 + ((rem>=3) ? 1 : 0);
      const int kd = kbar/6 + ((rem>=2) ? 1 : 0);
      const int ke = kbar/6 + ((rem>=1) ? 1 : 0);;
      const int kf = kbar/6;

      if(full || kbar==kk) {
        mzd_make_table(A, r, c, ka, T0, L0);
        mzd_make_table(A, r+ka, c, kb, T1, L1);
        mzd_make_table(A, r+ka+kb, c, kc, T2, L2);
        mzd_make_table(A, r+ka+kb+kc, c, kd, T3, L3);
        mzd_make_table(A, r+ka+kb+kc+kd, c, ke, T4, L4);
        mzd_make_table(A, r+ka+kb+kc+kd+ke, c, kf, T5, L5);
      }
      if(kbar==kk)
        mzd_process_rows6(A, r+kbar, A->nrows, c, kbar, T0, L0, T1, L1, T2, L2, T3, L3, T4, L4, T5, L5);
      if(full)
        mzd_process_rows6(A, 0, r, c, kbar, T0, L0, T1, L1, T2, L2, T3, L3, T4, L4, T5, L5);

  } else if (kbar>4*k) { 
      const int rem = kbar%5;
      const int ka = kbar/5 + ((rem>=4) ? 1 : 0);
      const int kb = kbar/5 + ((rem>=3) ? 1 : 0);
      const int kc = kbar/5 + ((rem>=2) ? 1 : 0);
      const int kd = kbar/5 + ((rem>=1) ? 1 : 0);
      const int ke = kbar/5;
      if(full || kbar==kk) {
        mzd_make_table(A, r, c, ka, T0, L0);
        mzd_make_table(A, r+ka, c, kb, T1, L1);
        mzd_make_table(A, r+ka+kb, c, kc, T2, L2);
        mzd_make_table(A, r+ka+kb+kc, c, kd, T3, L3);
        mzd_make_table(A, r+ka+kb+kc+kd, c, ke, T4, L4);
      }
      if(kbar==kk)
        mzd_process_rows5(A, r+kbar, A->nrows, c, kbar, T0, L0, T1, L1, T2, L2, T3, L3, T4, L4);
      if(full)
        mzd_process_rows5(A, 0, r, c, kbar, T0, L0, T1, L1, T2, L2, T3, L3, T4, L4);
      
    } else if (kbar>3*k) {
      const int rem = kbar%4;
      const int ka = kbar/4 + ((rem>=3) ? 1 : 0);
      const int kb = kbar/4 + ((rem>=2) ? 1 : 0);
      const int kc = kbar/4 + ((rem>=1) ? 1 : 0);
      const int kd = kbar/4;
      if(full || kbar==kk) {
        mzd_make_table(A, r, c, ka, T0, L0);
        mzd_make_table(A, r+ka, c, kb, T1, L1);
        mzd_make_table(A, r+ka+kb, c, kc, T2, L2);
        mzd_make_table(A, r+ka+kb+kc, c, kd, T3, L3);
      }
      if(kbar==kk)
        mzd_process_rows4(A, r+kbar, A->nrows, c, kbar, T0, L0, T1, L1, T2, L2, T3, L3);
      if(full)
        mzd_process_rows4(A, 0, r, c, kbar, T0, L0, T1, L1, T2, L2, T3, L3);
      
    } else if (kbar>2*k) {
      int rem = kbar%3;
      int ka = kbar/3 + ((rem>=2) ? 1 : 0);
      int kb = kbar/3 + ((rem>=1) ? 1 : 0);
      int kc = kbar/3;
      if(full || kbar==kk) {
        mzd_make_table(A, r, c, ka, T0, L0);
        mzd_make_table(A, r+ka, c, kb, T1, L1);
        mzd_make_table(A, r+ka+kb, c, kc, T2, L2);
      }
      if(kbar==kk)
        mzd_process_rows3(A, r+kbar, A->nrows, c, kbar, T0, L0, T1, L1, T2, L2);
      if(full)
        mzd_process_rows3(A, 0, r, c, kbar, T0, L0, T1, L1, T2, L2);
      
    } else if (kbar>k) {
      const int ka = kbar/2;
      const int kb = kbar - ka;
      if(full || kbar==kk) {
        mzd_make_table(A, r, c, ka, T0, L0);
        mzd_make_table(A, r+ka, c, kb, T1, L1);
      }
      if(kbar==kk)
        mzd_process_rows2(A, r+kbar, A->nrows, c, kbar, T0, L0, T1, L1);
      if(full)
        mzd_process_rows2(A, 0, r, c, kbar, T0, L0, T1, L1);
      
    } else if(kbar > 0) {
      if(full || kbar==kk) {
        mzd_make_table(A, r, c, kbar, T0, L0);
      }
      if(kbar==kk)
        mzd_process_rows(A, r+kbar, A->nrows, c, kbar, T0, L0);
      if(full)
        mzd_process_rows(A, 0, r, c, kbar, T0, L0);
    }

    if (!full) {
      _mzd_copy_back_rows(A, U, r, c, kbar);
    }

    r += kbar;
    c += kbar;
    if(kk!=kbar) {
      size_t cbar;
      size_t rbar;
      if (mzd_find_pivot(A, r, c, &rbar, &cbar)) {
        c = cbar;
        mzd_row_swap(A, r, rbar);
      } else {
        break;
      }
      //c++;
    }
  }

  mzd_free(T0);
  m4ri_mm_free(L0);
  mzd_free(T1);
  m4ri_mm_free(L1);
  mzd_free(T2);
  m4ri_mm_free(L2);
  mzd_free(T3);
  m4ri_mm_free(L3);
  mzd_free(T4);
  m4ri_mm_free(L4);
  mzd_free(T5);
  m4ri_mm_free(L5);
  mzd_free(U);
  return r;
}

void mzd_top_reduce_m4ri(packedmatrix *A, int k, packedmatrix *T, size_t *L) {
  const size_t ncols = A->ncols; 
  size_t r = 0;
  size_t c = 0;
  int kbar = 0;

  if (k == 0) {
    k = m4ri_opt_k(A->nrows, A->ncols, 0);
    if (k>5) {
      k -= 4;
    }
  }
  int kk = 4*k;

  packedmatrix *T0 = mzd_init(TWOPOW(k), A->ncols);
  packedmatrix *T1 = mzd_init(TWOPOW(k), A->ncols);
  packedmatrix *T2 = mzd_init(TWOPOW(k), A->ncols);
  packedmatrix *T3 = mzd_init(TWOPOW(k), A->ncols);
  size_t *L0 = (size_t *)m4ri_mm_calloc(TWOPOW(k), sizeof(size_t));
  size_t *L1 = (size_t *)m4ri_mm_calloc(TWOPOW(k), sizeof(size_t));
  size_t *L2 = (size_t *)m4ri_mm_calloc(TWOPOW(k), sizeof(size_t));
  size_t *L3 = (size_t *)m4ri_mm_calloc(TWOPOW(k), sizeof(size_t));

  while(c<ncols) {
    if(c+kk > A->ncols) {
      kk = ncols - c;
    }
    kbar = _mzd_gauss_submatrix_full(A, r, c, A->nrows, kk);

    if (kbar>3*k) {
      const int rem = kbar%4;
      const int ka = kbar/4 + ((rem>=3) ? 1 : 0);
      const int kb = kbar/4 + ((rem>=2) ? 1 : 0);
      const int kc = kbar/4 + ((rem>=1) ? 1 : 0);
      const int kd = kbar/4;
      mzd_make_table(A, r, c, ka, T0, L0);
      mzd_make_table(A, r+ka, c, kb, T1, L1);
      mzd_make_table(A, r+ka+kb, c, kc, T2, L2);
      mzd_make_table(A, r+ka+kb+kc, c, kd, T3, L3);
      mzd_process_rows4(A, 0, r, c, kbar, T0, L0, T1, L1, T2, L2, T3, L3);
      
    } else if (kbar>2*k) {
      int rem = kbar%3;
      int ka = kbar/3 + ((rem>=2) ? 1 : 0);
      int kb = kbar/3 + ((rem>=1) ? 1 : 0);
      int kc = kbar/3;
      mzd_make_table(A, r, c, ka, T0, L0);
      mzd_make_table(A, r+ka, c, kb, T1, L1);
      mzd_make_table(A, r+ka+kb, c, kc, T2, L2);
      mzd_process_rows3(A, 0, r, c, kbar, T0, L0, T1, L1, T2, L2);
      
    } else if (kbar>k) {
      const int ka = kbar/2;
      const int kb = kbar - ka;
      mzd_make_table(A, r, c, ka, T0, L0);
      mzd_make_table(A, r+ka, c, kb, T1, L1);
      mzd_process_rows2(A, 0, r, c, kbar, T0, L0, T1, L1);
      
    } else if(kbar > 0) {
      mzd_make_table(A, r, c, kbar, T0, L0);
      mzd_process_rows(A, 0, r, c, kbar, T0, L0);
    }
    r += kbar;
    c += kbar;
    if(kk!=kbar) {
      c++;
    }
  }

  mzd_free(T0);
  m4ri_mm_free(L0);
  mzd_free(T1);
  m4ri_mm_free(L1);
  mzd_free(T2);
  m4ri_mm_free(L2);
  mzd_free(T3);
  m4ri_mm_free(L3);
}

packedmatrix *mzd_invert_m4ri(packedmatrix *m, packedmatrix *I, int k) {
  packedmatrix *big = mzd_concat(NULL, m, I);
  size_t size=m->ncols;
  if (k == 0) {
    k = m4ri_opt_k(m->nrows, m->ncols, 0);
  }
  size_t twokay=TWOPOW(k);
  size_t i;
  packedmatrix *T=mzd_init(twokay, size*2);
  size_t *L=(size_t *)m4ri_mm_malloc(twokay * sizeof(size_t));
  packedmatrix *answer;
  
  mzd_reduce_m4ri(big, TRUE, k, T, L);
  
  for(i=0; i < size; i++) {
    if (!mzd_read_bit(big, i,i )) {
      answer = NULL;
      break;
    }
  }
  if (i == size)
    answer=mzd_submatrix(NULL, big, 0, size, size, size*2);
  
  m4ri_mm_free(L);
  mzd_free(T);
  mzd_free(big);
  
  return answer;
}

packedmatrix *mzd_mul_m4rm_t(packedmatrix *C, packedmatrix *A, packedmatrix *B, int k) {
  packedmatrix *AT, *BT, *CT;
  
  if(A->ncols != B->nrows) 
    m4ri_die("mzd_mul_m4rm_t: A ncols (%d) need to match B nrows (%d).\n", A->ncols, B->nrows);
  
  AT = mzd_transpose(NULL, A);
  BT = mzd_transpose(NULL, B);
  
  CT = mzd_init(B->ncols, A->nrows);
  CT = _mzd_mul_m4rm(CT, BT, AT, k, 0);
  
  mzd_free(AT);
  mzd_free(BT);

  C = mzd_transpose(C, CT);
  mzd_free(CT);
  return C;
}

packedmatrix *mzd_mul_m4rm(packedmatrix *C, packedmatrix *A, packedmatrix *B, int k) {
  size_t a = A->nrows;
  size_t c = B->ncols;

  if(A->ncols != B->nrows) 
    m4ri_die("mzd_mul_m4rm: A ncols (%d) need to match B nrows (%d).\n", A->ncols, B->nrows);
  if (C == NULL) {
    C = mzd_init(a, c);
  } else {
    if (C->nrows != a || C->ncols != c)
      m4ri_die("mzd_mul_m4rm: C (%d x %d) has wrong dimensions.\n", C->nrows, C->ncols);
  }
  return _mzd_mul_m4rm(C, A, B, k, TRUE);
}

packedmatrix *mzd_addmul_m4rm(packedmatrix *C, packedmatrix *A, packedmatrix *B, int k) {
  size_t a = A->nrows;
  size_t c = B->ncols;

  if(A->ncols != B->nrows) 
    m4ri_die("mzd_mul_m4rm A ncols (%d) need to match B nrows (%d) .\n", A->ncols, B->nrows);
  if (C == NULL) {
    C = mzd_init(a, c);
  } else {
    if (C->nrows != a || C->ncols != c)
      m4ri_die("mzd_mul_m4rm: C has wrong dimensions.\n");
  }
  return _mzd_mul_m4rm(C, A, B, k, FALSE);
}

#ifdef HAVE_SSE2
static inline void _mzd_combine8(word *c, word *t1, word *t2, word *t3, word *t4, word *t5, word *t6, word *t7, word *t8, int wide) {
  size_t i;
  /* assuming t1 ... t8 are aligned, but c might not be */
  if (ALIGNMENT(c,16)==0) {
    __m128i *__c = (__m128i*)c;
    __m128i *__t1 = (__m128i*)t1;
    __m128i *__t2 = (__m128i*)t2;
    __m128i *__t3 = (__m128i*)t3;
    __m128i *__t4 = (__m128i*)t4;
    __m128i *__t5 = (__m128i*)t5;
    __m128i *__t6 = (__m128i*)t6;
    __m128i *__t7 = (__m128i*)t7;
    __m128i *__t8 = (__m128i*)t8;
    const __m128i *eof = (__m128i*)((unsigned long)(c + wide) & ~0xF);
    __m128i xmm1;
    
    while(__c < eof) {
      xmm1 = _mm_xor_si128(*__c, *__t1++);
      xmm1 = _mm_xor_si128(xmm1, *__t2++);
      xmm1 = _mm_xor_si128(xmm1, *__t3++);
      xmm1 = _mm_xor_si128(xmm1, *__t4++);
      xmm1 = _mm_xor_si128(xmm1, *__t5++);
      xmm1 = _mm_xor_si128(xmm1, *__t6++);
      xmm1 = _mm_xor_si128(xmm1, *__t7++);
      xmm1 = _mm_xor_si128(xmm1, *__t8++);
      *__c++ = xmm1;
    }
    c  = (word*)__c;
    t1 = (word*)__t1;
    t2 = (word*)__t2;
    t3 = (word*)__t3;
    t4 = (word*)__t4;
    t5 = (word*)__t5;
    t6 = (word*)__t6;
    t7 = (word*)__t7;
    t8 = (word*)__t8;
    wide = ((sizeof(word)*wide)%16)/sizeof(word);
  }
  for(i=0; i<wide; i++) {
    c[i] ^= t1[i] ^ t2[i] ^ t3[i] ^ t4[i] ^ t5[i] ^ t6[i] ^ t7[i] ^ t8[i];
  }
}
#else

#define _mzd_combine8(c,t1,t2,t3,t4,t5,t6,t7,t8,wide) for(ii=0; ii<wide ; ii++) c[ii] ^= t1[ii] ^ t2[ii] ^ t3[ii] ^ t4[ii] ^ t5[ii] ^ t6[ii] ^ t7[ii] ^ t8[ii]

#endif

#ifdef HAVE_SSE2
static inline void _mzd_combine4(word *c, word *t1, word *t2, word *t3, word *t4, size_t wide) {
  size_t i;
  /* assuming t1 ... t4 are aligned, but c might not be */
  if (ALIGNMENT(c,16)==0) {
    __m128i *__c = (__m128i*)c;
    __m128i *__t1 = (__m128i*)t1;
    __m128i *__t2 = (__m128i*)t2;
    __m128i *__t3 = (__m128i*)t3;
    __m128i *__t4 = (__m128i*)t4;
    const __m128i *eof = (__m128i*)((unsigned long)(c + wide) & ~0xF);
    __m128i xmm1;
    
    while(__c < eof) {
      xmm1 = _mm_xor_si128(*__c, *__t1++);
      xmm1 = _mm_xor_si128(xmm1, *__t2++);
      xmm1 = _mm_xor_si128(xmm1, *__t3++);
      xmm1 = _mm_xor_si128(xmm1, *__t4++);
      *__c++ = xmm1;
    }
    c  = (word*)__c;
    t1 = (word*)__t1;
    t2 = (word*)__t2;
    t3 = (word*)__t3;
    t4 = (word*)__t4;
    wide = ((sizeof(word)*wide)%16)/sizeof(word);
  }
  for(i=0; i<wide; i++) {
    c[i] ^= t1[i] ^ t2[i] ^ t3[i] ^ t4[i];
  }
}
#else

#define _mzd_combine4(c, t1, t2, t3, t4, wide) for(ii=0; ii<wide ; ii++) c[ii] ^= t1[ii] ^ t2[ii] ^ t3[ii] ^ t4[ii]

#endif //HAVE_SSE2

#ifdef HAVE_SSE2
static inline void _mzd_combine2(word *c, word *t1, word *t2, size_t wide) {
  size_t i;
  /* assuming t1 ... t2 are aligned, but c might not be */
  if (ALIGNMENT(c,16)==0) {
    __m128i *__c = (__m128i*)c;
    __m128i *__t1 = (__m128i*)t1;
    __m128i *__t2 = (__m128i*)t2;
    const __m128i *eof = (__m128i*)((unsigned long)(c + wide) & ~0xF);
    __m128i xmm1;
    
    while(__c < eof) {
      xmm1 = _mm_xor_si128(*__c, *__t1++);
      xmm1 = _mm_xor_si128(xmm1, *__t2++);
      *__c++ = xmm1;
    }
    c  = (word*)__c;
    t1 = (word*)__t1;
    t2 = (word*)__t2;
    wide = ((sizeof(word)*wide)%16)/sizeof(word);
  }
  for(i=0; i<wide; i++) {
    c[i] ^= t1[i] ^ t2[i];
  }
}
#else

#define _mzd_combine2(c, t1, t2, wide) for(ii=0; ii<wide ; ii++) c[ii] ^= t1[ii] ^ t2[ii]

#endif //HAVE_SSE2


#ifdef M4RM_GRAY8
#define _MZD_COMBINE _mzd_combine8(c, t1, t2, t3, t4, t5, t6, t7, t8, wide)
#else //M4RM_GRAY8
#define _MZD_COMBINE _mzd_combine4(c, t1, t2, t3, t4, wide)
#endif //M4RM_GRAY8

packedmatrix *_mzd_mul_m4rm(packedmatrix *C, packedmatrix *A, packedmatrix *B, int k, int clear) {
  /**
   * The algorithm proceeds as follows:
   * 
   * Step 1. Make a Gray code table of all the \f$2^k\f$ linear combinations
   * of the \f$k\f$ rows of \f$B_i\f$.  Call the \f$x\f$-th row
   * \f$T_x\f$.
   *
   * Step 2. Read the entries 
   *    \f$a_{j,(i-1)k+1}, a_{j,(i-1)k+2} , ... , a_{j,(i-1)k+k}.\f$
   *
   * Let \f$x\f$ be the \f$k\f$ bit binary number formed by the
   * concatenation of \f$a_{j,(i-1)k+1}, ... , a_{j,ik}\f$.
   *
   * Step 3. for \f$h = 1,2, ... , c\f$ do
   *   calculate \f$C_{jh} = C_{jh} + T_{xh}\f$.
   */
  assert(C->offset==0);
  size_t i,j;
  size_t ii;
  unsigned int x1, x2, x3, x4;
  word *t1, *t2, *t3, *t4;

#ifdef M4RM_GRAY8
  unsigned int x5, x6, x7, x8;
  word *t5, *t6, *t7, *t8;
#endif

  word *c;

  size_t a_nr = A->nrows;
  size_t a_nc = A->ncols;
  size_t b_nc = B->ncols;

  if (b_nc < RADIX-10) {
    if(clear)
      return mzd_mul_naive(C, A, B);
    else
      return mzd_addmul_naive(C, A, B);
  } else if (a_nr < 16) {
    return _mzd_mul_va(C, A, B, clear);
  }

  size_t wide = C->width;

  /* clear first */
  if (clear) {
    mzd_set_ui(C, 0);
  }

  const size_t blocksize = MZD_MUL_BLOCKSIZE;

  if (k == 0) {
    k = m4ri_opt_k(blocksize, a_nc, b_nc);
#ifdef M4RM_GRAY8
    if (k>3)
      k -= 2;
    /* reduce k further if that has a chance of hitting L1 */
    const size_t tsize = (int)(0.8*(TWOPOW(k) * b_nc));
    if(tsize > CPU_L1_CACHE && tsize/2 <= CPU_L1_CACHE)
      k -= 1;
#else
    if (k>2)
      k -= 1;
#endif
  }

#ifndef M4RM_GRAY8
  size_t *buffer = (size_t*)m4ri_mm_malloc(4 * TWOPOW(k) * sizeof(size_t));
#else
  size_t *buffer = (size_t*)m4ri_mm_malloc(8 * TWOPOW(k) * sizeof(size_t));
#endif

  packedmatrix *T1 = mzd_init(TWOPOW(k), b_nc);
  size_t *L1 = buffer;
  packedmatrix *T2 = mzd_init(TWOPOW(k), b_nc);
  size_t *L2 = buffer + 1*TWOPOW(k);
  packedmatrix *T3 = mzd_init(TWOPOW(k), b_nc);
  size_t *L3 = buffer + 2*TWOPOW(k);
  packedmatrix *T4 = mzd_init(TWOPOW(k), b_nc);
  size_t *L4 = buffer + 3*TWOPOW(k);

#ifdef M4RM_GRAY8
  packedmatrix *T5 = mzd_init(TWOPOW(k), b_nc);
  size_t *L5 = buffer + 4*TWOPOW(k);
  packedmatrix *T6 = mzd_init(TWOPOW(k), b_nc);
  size_t *L6 = buffer + 5*TWOPOW(k);
  packedmatrix *T7 = mzd_init(TWOPOW(k), b_nc);
  size_t *L7 = buffer + 6*TWOPOW(k);
  packedmatrix *T8 = mzd_init(TWOPOW(k), b_nc);
  size_t *L8 = buffer + 7*TWOPOW(k);
#endif

  /* process stuff that fits into multiple of k first, but blockwise (babystep-giantstep)*/
  size_t babystep, giantstep;
#ifdef M4RM_GRAY8
  const int kk = 8*k;
#else
  const int kk = 4*k;
#endif
  const size_t end = a_nc/kk;

  for (giantstep=0; giantstep + blocksize <= a_nr; giantstep += blocksize) {
    for(i=0; i < end; i++) {
      mzd_make_table( B, i*kk, 0, k, T1, L1);
      mzd_make_table( B, i*kk+k, 0, k, T2, L2);
      mzd_make_table( B, i*kk+k+k, 0, k, T3, L3);
      mzd_make_table( B, i*kk+k+k+k, 0, k, T4, L4);
#ifdef M4RM_GRAY8
      mzd_make_table( B, i*kk+k+k+k+k, 0, k, T5, L5);
      mzd_make_table( B, i*kk+k+k+k+k+k, 0, k, T6, L6);
      mzd_make_table( B, i*kk+k+k+k+k+k+k, 0, k, T7, L7);
      mzd_make_table( B, i*kk+k+k+k+k+k+k+k, 0, k, T8, L8);
#endif   

      for(babystep = 0; babystep < blocksize; babystep++) {
        j = giantstep + babystep;
        x1 = L1[ (int)mzd_read_bits(A, j, i*kk, k) ];
        x2 = L2[ (int)mzd_read_bits(A, j, i*kk+k, k) ];
        x3 = L3[ (int)mzd_read_bits(A, j, i*kk+k+k, k) ];
        x4 = L4[ (int)mzd_read_bits(A, j, i*kk+k+k+k, k) ];
#ifdef M4RM_GRAY8
        x5 = L5[ (int)mzd_read_bits(A, j, i*kk+k+k+k+k, k) ];
        x6 = L6[ (int)mzd_read_bits(A, j, i*kk+k+k+k+k+k, k) ];
        x7 = L7[ (int)mzd_read_bits(A, j, i*kk+k+k+k+k+k+k, k) ];
        x8 = L8[ (int)mzd_read_bits(A, j, i*kk+k+k+k+k+k+k+k, k) ];
#endif
        c = C->values + C->rowswap[j];
        t1 = T1->values + T1->rowswap[x1];
        t2 = T2->values + T2->rowswap[x2];
        t3 = T3->values + T3->rowswap[x3];
        t4 = T4->values + T4->rowswap[x4];
#ifdef M4RM_GRAY8
        t5 = T5->values + T5->rowswap[x5];
        t6 = T6->values + T6->rowswap[x6];
        t7 = T7->values + T7->rowswap[x7];
        t8 = T8->values + T8->rowswap[x8];
#endif
        _MZD_COMBINE;
      }
    }
  }
  
  for(i=0; i < end; i++) {
    mzd_make_table( B, i*kk, 0, k, T1, L1);
    mzd_make_table( B, i*kk+k, 0, k, T2, L2);
    mzd_make_table( B, i*kk+k+k, 0, k, T3, L3);
    mzd_make_table( B, i*kk+k+k+k, 0, k, T4, L4);
#ifdef M4RM_GRAY8
    mzd_make_table( B, i*kk+k+k+k+k, 0, k, T5, L5);
    mzd_make_table( B, i*kk+k+k+k+k+k, 0, k, T6, L6);
    mzd_make_table( B, i*kk+k+k+k+k+k+k, 0, k, T7, L7);
    mzd_make_table( B, i*kk+k+k+k+k+k+k+k, 0, k, T8, L8);
#endif
    for(babystep = 0; babystep < a_nr - giantstep; babystep++) {
      j = giantstep + babystep;
      x1 = L1[ (int)mzd_read_bits(A, j, i*kk, k) ];
      x2 = L2[ (int)mzd_read_bits(A, j, i*kk+k, k) ];
      x3 = L3[ (int)mzd_read_bits(A, j, i*kk+k+k, k) ];
      x4 = L4[ (int)mzd_read_bits(A, j, i*kk+k+k+k, k) ];
#ifdef M4RM_GRAY8
      x5 = L5[ (int)mzd_read_bits(A, j, i*kk+k+k+k+k, k) ];
      x6 = L6[ (int)mzd_read_bits(A, j, i*kk+k+k+k+k+k, k) ];
      x7 = L7[ (int)mzd_read_bits(A, j, i*kk+k+k+k+k+k+k, k) ];
      x8 = L8[ (int)mzd_read_bits(A, j, i*kk+k+k+k+k+k+k+k, k) ];
#endif
      c = C->values + C->rowswap[j];
      t1 = T1->values + T1->rowswap[x1];
      t2 = T2->values + T2->rowswap[x2];
      t3 = T3->values + T3->rowswap[x3];
      t4 = T4->values + T4->rowswap[x4];
#ifdef M4RM_GRAY8
      t5 = T5->values + T5->rowswap[x5];
      t6 = T6->values + T6->rowswap[x6];
      t7 = T7->values + T7->rowswap[x7];
      t8 = T8->values + T8->rowswap[x8];
#endif
      _MZD_COMBINE;
    }
  }

  /* handle stuff that doesn't fit into multiple of kk */
  if (a_nc%kk) {
    for (i=end*kk/k; i < (a_nc)/k; i++) {
      mzd_make_table( B, i*k, 0, k, T1, L1);
      for(j = 0; j<a_nr; j++) {
        x1 = L1[ (int)mzd_read_bits(A, j, i*k, k) ];
        c = C->values + C->rowswap[j];
        t1 = T1->values + T1->rowswap[x1];
        for(ii=0; ii<wide; ii++) {
          c[ii] ^= t1[ii];
        }
      }
    }
    /* handle stuff that doesn't fit into multiple of k */
    if (a_nc%k) {
      mzd_make_table( B, a_nc/k * k , 0, a_nc%k, T1, L1);
      for(j = 0; j<a_nr; j++) {
        x1 = L1[ (int)mzd_read_bits(A, j, i*k, a_nc%k) ];
        c = C->values + C->rowswap[j];
        t1 = T1->values + T1->rowswap[x1];
        for(ii=0; ii<wide; ii++) {
          c[ii] ^= t1[ii];
        }
      }
    }
  }

  mzd_free(T1);
  mzd_free(T2);
  mzd_free(T3);
  mzd_free(T4);
#ifdef M4RM_GRAY8
  mzd_free(T5);
  mzd_free(T6);
  mzd_free(T7);
  mzd_free(T8);
#endif
  m4ri_mm_free(buffer);
  return C;
}