RandomPower2.hpp
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/**
* \file RandomPower2.hpp
* \brief Header for RandomPower2.
*
* Return and multiply by powers of two.
*
* Copyright (c) Charles Karney (2006-2011) <charles@karney.com> and licensed
* under the MIT/X11 License. For more information, see
* http://randomlib.sourceforge.net/
**********************************************************************/
#if !defined(RANDOMLIB_RANDOMPOWER2_HPP)
#define RANDOMLIB_RANDOMPOWER2_HPP 1
#include <cmath> // For std::pow
namespace RandomLib {
/**
* \brief Return or multiply by powers of 2
*
* With some compilers it's fastest to do a table lookup of powers of
* 2. If RANDOMLIB_POWERTABLE is 1, a lookup table is used. If
* RANDOMLIB_POWERTABLE is 0, then std::pow is used.
**********************************************************************/
class RANDOMLIB_EXPORT RandomPower2 {
public:
/**
* Return powers of 2 (either using a lookup table or std::pow)
*
* @param[in] n the integer power.
* @return 2<sup><i>n</i></sup>.
**********************************************************************/
template<typename RealType> static inline RealType pow2(int n) throw() {
#if RANDOMLIB_POWERTABLE
return RealType(power2[n - minpow]);
#else
return std::pow(RealType(2), n);
#endif
}
/**
* Multiply a real by a power of 2
*
* @tparam RealType the type of \e x.
* @param[in] x the real number.
* @param[in] n the power (positive or negative).
* @return \e x 2<sup><i>n</i></sup>.
**********************************************************************/
template<typename RealType>
static inline RealType shiftf(RealType x, int n) throw()
// std::ldexp(x, n); is equivalent, but slower
{ return x * pow2<RealType>(n); }
// Constants
enum {
/**
* Minimum power in RandomPower2::power2
**********************************************************************/
#if RANDOMLIB_LONGDOUBLEPREC > 64
minpow = -120,
#else
minpow = -64,
#endif
maxpow = 64 /**< Maximum power in RandomPower2::power2. */
};
private:
#if RANDOMLIB_POWERTABLE
/**
* Table of powers of two
**********************************************************************/
static const float power2[maxpow - minpow + 1]; // Powers of two
#endif
};
} // namespace RandomLib
#endif // RANDOMLIB_RANDOMPOWER2_HPP