bitsubsetgray.h

the FXT library: fast transforms and low level algorithms. The package contains many algorithms for

#if !defined HAVE_BITSUBSETGRAY_H__
#define      HAVE_BITSUBSETGRAY_H__

#include "bits/graycode.h"
#include "fxttypes.h"


class bit_subset_gray
// generate all all subsets of bits of  a given word
// in minimal-change (Gray code) order.
//
// e.g. for the word ('.' printed for unset bits)
//   ...11.1.
// these words are produced by subsequent next()-calls:
//   ......1.
//   ....1...
//   ....1.1.  *** NOT a Gray code in geenral ***
//   ...11...
//   ...11.1.
//   ...1....
//   ...1..1.
//   ........
//
{
public:
    ulong u_, v_;

public:
    bit_subset_gray(ulong v) : u_(0), v_(v)  { ; }
    ~bit_subset_gray() { ; }
    ulong current()  const { return u_; }
    ulong out(ulong x)  { return gray_code(x) & v_; }
    ulong next()  { u_ = (u_ - v_) & v_;  return out(u_); }
    ulong prev()  { u_ = (u_ - 1 ) & v_;  return out(u_); }
};
// -------------------------


#endif  // !defined HAVE_BITSUBSETGRAY_H__