dox/Common/vtkFastNumericConversion.h

Go to the documentation of this file.

/*=========================================================================

  Program:   Visualization Toolkit
  Module:    vtkFastNumericConversion.h

  Copyright (c) Ken Martin, Will Schroeder, Bill Lorensen
  All rights reserved.
  See Copyright.txt or http://www.kitware.com/Copyright.htm for details.

     This software is distributed WITHOUT ANY WARRANTY; without even
     the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR
     PURPOSE.  See the above copyright notice for more information.

=========================================================================*/
#ifndef __vtkFastNumericConversion_h
#define __vtkFastNumericConversion_h

#include "vtkObject.h"

// Use the bit-representation trick only on X86, and only when producing
// optimized code
#if defined(NDEBUG) && (defined i386 || defined _M_IX86)
#define VTK_USE_TRICK
#endif

// Linux puts the FPU in extended precision. Windows and FreeBSD keep it in
// double precision.  If other operating systems for i386 (Solaris?) behave
// like Linux, add them below.  Special care needs to be taken when dealing
// with extended precision mode because even though we are eventually writing
// out to a double-precision variable to capture the fixed-point or integer
// results, the extra bits maintained in the internal computations disrupt
// the bit-playing that we're doing here.
#if defined(__linux__)
#define VTK_EXT_PREC
#endif

//#define VTK_TEST_HACK_TO_EMULATE_LINUX_UNDER_WINDOWS
#ifdef VTK_TEST_HACK_TO_EMULATE_LINUX_UNDER_WINDOWS
#define VTK_EXT_PREC
#endif


class VTK_COMMON_EXPORT vtkFastNumericConversion : public vtkObject
{
public:
  static vtkFastNumericConversion *New();
  vtkTypeMacro(vtkFastNumericConversion, vtkObject);
  void PrintSelf(ostream& os, vtkIndent indent);

  int TestQuickFloor(double val)
    {
    return vtkFastNumericConversion::QuickFloor(val);
    }

  int TestSafeFloor(double val)
    {
    return vtkFastNumericConversion::SafeFloor(val);
    }

  int TestRound(double val)
    {
    return vtkFastNumericConversion::Round(val);
    }

  int TestConvertFixedPointIntPart(double val)
    {
    int frac;
    return ConvertFixedPoint(val, frac);
    }

  int TestConvertFixedPointFracPart(double val)
    {
    int frac;
    ConvertFixedPoint(val, frac);
    return frac;
    }

protected:
  //BTX
  static inline double BorrowBit() { return 1.5;};


  static inline double two30()
    {
      return static_cast<double>(static_cast<unsigned long>(1) << 30);
    }


  static inline double two52()
    {
      return (static_cast<unsigned long>(1) << (52-30)) * two30();
    }


  static inline double two51()
    {
      return (static_cast<unsigned long>(1) << (51-30)) * two30();
    }


  static inline double two63()
    {
      return (static_cast<unsigned long>(1) << (63-60)) * two30() * two30();
    }


  static inline double two62()
    {
      return (static_cast<unsigned long>(1) << (62-60)) * two30() * two30();
    }

  // Define number of bits of precision for various data types.
  // Note: INT_BITS is really 31, (rather than 32, since one of the bits is
  // just used for the two's-complement sign), but we say 30 because we don't
  // need to be able to handle 31-bit magnitudes correctly. I say that
  // because this is used for the QuickFloor code, and the SafeFloor code
  // retains an extra bit of fixed point precision which it shifts-out at the
  // end, thus reducing the magnitude of integers that it can handle. That's
  // an inherent limitation of using SafeFloor to prevent round-ups under any
  // circumstances, and there's no need to make QuickFloor handle a wider
  // range of numbers than SafeFloor.
#define INT_BITS 30
#define EXT_BITS 64
#define DBL_BITS 53


public:
#ifdef VTK_EXT_PREC
  // Compute (0.5 ^ (EXT_BITS-INT_BITS)) as a compile-time constant
  static inline double RoundingTieBreaker()
    {
      return 1.0 / (two30() * (static_cast<unsigned long>(1) << (EXT_BITS - INT_BITS - 30)));
    }
#else
  // Compute (0.5 ^ (DBL_BITS-INT_BITS)) as a compile-time constant
  static inline double RoundingTieBreaker()
    {
      return 1.0 / (static_cast<unsigned long>(1) << (DBL_BITS - INT_BITS));
    }
#endif


protected:

  static inline double QuickFloorDenormalizer()
    {return two52() * BorrowBit(); };


  static inline double SafeFloorDenormalizer()
    { return two51() * BorrowBit(); };


  static inline double QuickExtPrecTempDenormalizer()
    {return two63() * BorrowBit(); };


  static inline double SafeExtPrecTempDenormalizer()
    {return two62() * BorrowBit(); };

  static inline double QuickRoundAdjust() {return 0.5;};
  static inline double SafeRoundAdjust() {return 0.25;};
  static inline int SafeFinalShift() {return 1;};


#ifdef VTK_WORDS_BIGENDIAN
  enum {exponent_pos = 0, mantissa_pos = 1};
#else
  enum {exponent_pos = 1, mantissa_pos = 0};
#endif
  //ETX

public:


  void SetReservedFracBits(int bits)
    {
    // Add one to the requested number of fractional bits, to make
    // the conversion safe with respect to rounding mode. This is the
    // same as the difference between QuickFloor and SafeFloor.
    bits++;
    unsigned long mtime = this->GetMTime();
    this->SetinternalReservedFracBits(bits);
    if (mtime != this->GetMTime())
      {
      this->InternalRebuild();
      }
    };

  //BTX

  inline static int QuickFloor(const double &val)
    {
#ifdef VTK_USE_TRICK
      union { int i[2]; double d; } u;
#ifdef VTK_EXT_PREC
      u.d = (((val - (QuickRoundAdjust() - RoundingTieBreaker()))
              // Push off those extended precision bits
              + QuickExtPrecTempDenormalizer())
             // Pull back the wanted bits into double range
             - QuickExtPrecTempDenormalizer())
        + QuickFloorDenormalizer();
#else // ! VTK_EXT_PREC
      u.d = (val - (QuickRoundAdjust() - RoundingTieBreaker()))
        + QuickFloorDenormalizer();
#endif // VTK_EXT_PREC
      return u.i[mantissa_pos];
#else // ! VTK_USE_TRICK
      return static_cast<int>(val);
#endif // VTK_USE_TRICK
    }


  inline static int SafeFloor(const double &val)
    {
#ifdef VTK_USE_TRICK
      union { int i[2]; double d; } u;
#ifdef VTK_EXT_PREC
      u.d = (((val - SafeRoundAdjust())
              + SafeExtPrecTempDenormalizer())
             - SafeExtPrecTempDenormalizer())
        + SafeFloorDenormalizer();
#else // ! VTK_EXT_PREC
      u.d = (val - SafeRoundAdjust())
        + SafeFloorDenormalizer();
#endif // VTK_EXT_PREC
      return u.i[mantissa_pos] >> SafeFinalShift();
#else // ! VTK_USE_TRICK
      return static_cast<int>(val);
#endif // VTK_USE_TRICK
    }


  inline static int Round(const double &val)
    {
#ifdef VTK_USE_TRICK
      union { int i[2]; double d; } u;
#ifdef VTK_EXT_PREC
      u.d = ((val
              + QuickExtPrecTempDenormalizer())
             - QuickExtPrecTempDenormalizer())
        + QuickFloorDenormalizer();
#else // ! VTK_EXT_PREC
      u.d = val
        + QuickFloorDenormalizer();
#endif // VTK_EXT_PREC
    return u.i[mantissa_pos];
#else // ! VTK_USE_TRICK
    if (val>=0)
      {
      return static_cast<int>(val + 0.5);
      }
    else
      {
      return static_cast<int>(val - 0.5);
      }
#endif // VTK_USE_TRICK
    }


  inline int ConvertFixedPoint(const double &val, int &fracPart)
    {
      union { int i[2]; double d; } u;
#ifdef VTK_EXT_PREC
      u.d = (((val - fixRound)
              + this->epTempDenormalizer)
             - this->epTempDenormalizer)
        + this->fpDenormalizer;
#else // ! VTK_EXT_PREC
      u.d = (val - fixRound)
        + this->fpDenormalizer;
#endif // VTK_EXT_PREC
    fracPart = (u.i[mantissa_pos] & fracMask) >> 1;
    return u.i[mantissa_pos] >> this->internalReservedFracBits;
    }
  //ETX


protected:
  //BTX
  vtkFastNumericConversion()
    {
#ifdef VTK_TEST_HACK_TO_EMULATE_LINUX_UNDER_WINDOWS
    _controlfp( _PC_64, MCW_PC );
#endif

    this->fixRound = 0;
    this->internalReservedFracBits = 0;
    this->fracMask = 0;
    this->fpDenormalizer = 0;
    };
  ~vtkFastNumericConversion() {};
  void InternalRebuild(void);

private:
  vtkSetMacro(internalReservedFracBits, int);
  vtkGetMacro(internalReservedFracBits, int);
  int internalReservedFracBits;
  int fracMask;

  // Used when doing fixed point conversions with a certain number of bits
  // remaining for the fractional part, as opposed to the pure integer
  // flooring
  double fpDenormalizer;

  // Used when doing fixed point conversions in extended precision mode
  double epTempDenormalizer;

  // Adjustment for rounding based on the number of bits reserved for
  // fractional representation
  double fixRound;
  //ETX

  vtkFastNumericConversion(const vtkFastNumericConversion&); // Not implemented
  void operator=(const vtkFastNumericConversion&); // Not implemented
};

#endif