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