IeeeHalf.hpp

// Copyright (c) 2018 Graphcore Ltd. All rights reserved.
 
/*********************************************************************
 * Half-precision floating-point abstraction for Colossus
 * Instruction Set Simulator
 *
 * Notes:
 *   Most operations are performed by:
 *     1 Converting the half-precision value to single-precision (float)
 *     2 Performing the operation at single-precision accuracy
 *     3 Converting the result back to half-precision
 *
 *********************************************************************/
 
#ifndef poplar_IeeeHalf_hpp
#define poplar_IeeeHalf_hpp
 
#include <stdint.h>
 
namespace poplar {
 
class IeeeHalf {
 
public:
  IeeeHalf() = default;
 
  IeeeHalf(float value);
 
  static IeeeHalf fromBits(uint16_t bitPattern);
 
  operator float() const;
 
  uint16_t bit16() const { return ihalf; }
 
  uint32_t bitz32() const { return (uint32_t)ihalf; }
 
  // Destructive operators
  IeeeHalf &operator=(const IeeeHalf &other) = default;
  IeeeHalf &operator+=(float other);
  IeeeHalf &operator-=(float other);
  IeeeHalf &operator*=(float other);
  IeeeHalf &operator/=(float other);
 
  // Comparison operators.
  bool operator<(float other) const;
  bool operator>(float other) const;
  bool operator<=(float other) const;
  bool operator>=(float other) const;
  bool operator==(IeeeHalf other) const;
  bool operator!=(IeeeHalf other) const;
 
  // These are necessary to avoid ambiguous comparisons when doing
  // `IeeeHalf == float`, because we could either convert the first parameter
  // to a float, or the second to an IeeeHalf. To avoid the ambiguity we provide
  // functions that require no conversion (internally they convert *this
  // to a float and then compare). The same is true for double.
  bool operator==(float other) const;
  bool operator!=(float other) const;
 
  // Unary negation.
  IeeeHalf operator-() const;
 
  // Basic arithmetic operators.
  IeeeHalf operator+(float other);
  IeeeHalf operator-(float other);
  IeeeHalf operator*(float other);
  IeeeHalf operator/(float other);
 
  bool isqNaN() const;
  bool issNaN() const;
  bool isNaN() const;
  bool isInf() const;
  bool isNorm() const;
  bool isZero() const;
 
private:
  uint16_t ihalf;
};
 
} // namespace poplar
 
#endif // poplar_IeeeHalf_hpp