fast_exp.hpp

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//=======================================================================
// Copyright (c) 2013 Piotr Wygocki
//
// Distributed under the Boost Software License, Version 1.0. (See
// accompanying file LICENSE_1_0.txt or copy at
// http://www.boost.org/LICENSE_1_0.txt)
//=======================================================================
#ifndef PAAL_FAST_EXP_HPP
#define PAAL_FAST_EXP_HPP

#include <cstdint>
#include <cmath>

namespace paal {

inline float fast_pow2(float p) {
    float clipp = (p < -126) ? -126.0f : p;
    union {
        uint32_t i;
        float f;
    } v = { static_cast<uint32_t>((1 << 23) * (clipp + 126.94269504f)) };
    return v.f;
}

inline float fast_exp(float p) {
    static const float multiplier = 1 / std::log(2);
    return fast_pow2(multiplier * p);
}
} 

#endif // PAAL_FAST_EXP_HPP