graycode.h

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#ifndef M4RI_GRAYFLEX_H
#define M4RI_GRAYFLEX_H

/******************************************************************************
*
*                 M4RI: Linear Algebra over GF(2)
*
*    Copyright (C) 2007 Gregory Bard <gregory.bard@ieee.org> 
*    Copyright (C) 2007 Martin Albrecht <malb@informatik.uni-bremen.de> 
*
*  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/
******************************************************************************/
 
#define __M4RI_MAXKAY 16

typedef struct {
  int *ord;
  int *inc;
} code;

extern code **m4ri_codebook;

int m4ri_gray_code(int i, int l);

void m4ri_build_code(int *ord, int *inc, int l);

void m4ri_build_all_codes(void);

void m4ri_destroy_all_codes(void);

static inline int log2_floor(int v) {
  static unsigned const int b[] = { 0x2, 0xC, 0xF0, 0xFF00, 0xFFFF0000 };
  static unsigned const int S[] = { 1, 2, 4, 8, 16 };
  unsigned int r = 0;
  for (int i = 4; i >= 0; --i)
  {
    if ((v & b[i]))
    {
      v >>= S[i];
      r |= S[i];
    }
  }
  return r;
}


int m4ri_opt_k(int a,int b,int c);

#endif // M4RI_GRAYFLEX_H