uniform.hpp

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/*
Copyright 2010-2011, D. E. Shaw Research.
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  contributors may be used to endorse or promote products derived from
  this software without specific prior written permission.

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#ifndef __r123_uniform_dot_hpp
#define __r123_uniform_dot_hpp

#include <Random123/features/compilerfeatures.h>
#include <limits>
#if R123_USE_CXX11_TYPE_TRAITS
#include <type_traits>
#endif
#if __cplusplus >= 201103L
#include <array>
#endif

namespace r123{
#if R123_USE_CXX11_TYPE_TRAITS
using std::make_signed;
using std::make_unsigned;
#else
// Sigh... We could try to find another <type_traits>, e.g., from
// boost or TR1.  Or we can do it ourselves in the r123 namespace.
// It's not clear which will cause less headache...
template <typename T> struct make_signed{};
template <typename T> struct make_unsigned{};
#define R123_MK_SIGNED_UNSIGNED(ST, UT)                 \
template<> struct make_signed<ST>{ typedef ST type; }; \
template<> struct make_signed<UT>{ typedef ST type; }; \
template<> struct make_unsigned<ST>{ typedef UT type; }; \
template<> struct make_unsigned<UT>{ typedef UT type; }

R123_MK_SIGNED_UNSIGNED(int8_t, uint8_t);
R123_MK_SIGNED_UNSIGNED(int16_t, uint16_t);
R123_MK_SIGNED_UNSIGNED(int32_t, uint32_t);
R123_MK_SIGNED_UNSIGNED(int64_t, uint64_t);
#if R123_USE_GNU_UINT128
R123_MK_SIGNED_UNSIGNED(__int128_t, __uint128_t);
#endif
#undef R123_MK_SIGNED_UNSIGNED
#endif

#if defined(__CUDACC__) || defined(_LIBCPP_HAS_NO_CONSTEXPR)
// Amazing! cuda thinks numeric_limits::max() is a __host__ function, so
// we can't use it in a device function.  
//
// The LIBCPP_HAS_NO_CONSTEXP test catches situations where the libc++
// library thinks that the compiler doesn't support constexpr, but we
// think it does.  As a consequence, the library declares
// numeric_limits::max without constexpr.  This workaround should only
// affect a narrow range of compiler/library pairings.
// 
// In both cases, we find max() by computing ~(unsigned)0 right-shifted
// by is_signed.
template <typename T>
R123_CONSTEXPR R123_STATIC_INLINE R123_CUDA_DEVICE T maxTvalue(){
    typedef typename make_unsigned<T>::type uT;
    return (~uT(0)) >> std::numeric_limits<T>::is_signed;
 }
#else
template <typename T>
R123_CONSTEXPR R123_STATIC_INLINE T maxTvalue(){
    return std::numeric_limits<T>::max();
}
#endif


template <typename Ftype, typename Itype>
R123_CUDA_DEVICE R123_STATIC_INLINE Ftype u01(Itype in){
    typedef typename make_unsigned<Itype>::type Utype;
    R123_CONSTEXPR Ftype factor = Ftype(1.)/(maxTvalue<Utype>() + Ftype(1.));
    R123_CONSTEXPR Ftype halffactor = Ftype(0.5)*factor;
#if R123_UNIFORM_FLOAT_STORE
    volatile Ftype x = Utype(in)*factor; return x+halffactor;
#else
    return Utype(in)*factor + halffactor;
#endif
}


template <typename Ftype, typename Itype>
R123_CUDA_DEVICE R123_STATIC_INLINE Ftype uneg11(Itype in){
    typedef typename make_signed<Itype>::type Stype;
    R123_CONSTEXPR Ftype factor = Ftype(1.)/(maxTvalue<Stype>() + Ftype(1.));
    R123_CONSTEXPR Ftype halffactor = Ftype(0.5)*factor;
#if R123_UNIFORM_FLOAT_STORE
    volatile Ftype x = Stype(in)*factor; return x+halffactor;
#else
    return Stype(in)*factor + halffactor;
#endif
}


template <typename Ftype, typename Itype>
R123_CUDA_DEVICE R123_STATIC_INLINE Ftype u01fixedpt(Itype in){
    typedef typename make_unsigned<Itype>::type Utype;
    R123_CONSTEXPR int excess = std::numeric_limits<Utype>::digits - std::numeric_limits<Ftype>::digits;
    if(excess>=0){
        R123_CONSTEXPR int ex_nowarn = (excess>=0) ? excess : 0;
        R123_CONSTEXPR Ftype factor = Ftype(1.)/(Ftype(1.) + ((maxTvalue<Utype>()>>ex_nowarn)));
        return (1 | (Utype(in)>>ex_nowarn)) * factor;
    }else
        return u01<Ftype>(in);
}

#if R123_USE_CXX11_STD_ARRAY


template <typename Ftype, typename CollType>
static inline
std::array<Ftype, CollType::static_size> u01all(CollType in)
{
    std::array<Ftype, CollType::static_size> ret;
    size_t i=0;
    for(auto e : in){
        ret[i++] = u01<Ftype>(e);
    }
    return ret;
}


template <typename Ftype, typename CollType>
static inline
std::array<Ftype, CollType::static_size> uneg11all(CollType in)
{
    std::array<Ftype, CollType::static_size> ret;
    size_t i=0;
    for(auto e : in){
        ret[i++] = uneg11<Ftype>(e);
    }
    return ret;
}


template <typename Ftype, typename CollType>
static inline
std::array<Ftype, CollType::static_size> u01fixedptall(CollType in)
{
    std::array<Ftype, CollType::static_size> ret;
    size_t i=0;
    for(auto e : in){
        ret[i++] = u01fixedpt<Ftype>(e);
    }
    return ret;
}
#endif // __cplusplus >= 201103L

} // namespace r123

#endif