138 lines
4.5 KiB
C++
138 lines
4.5 KiB
C++
/// @ref gtx_fast_exponential
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/// @file glm/gtx/fast_exponential.inl
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namespace glm
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{
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// fastPow:
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template <typename genType>
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GLM_FUNC_QUALIFIER genType fastPow(genType x, genType y)
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{
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return exp(y * log(x));
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}
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template <typename T, precision P, template <typename, precision> class vecType>
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GLM_FUNC_QUALIFIER vecType<T, P> fastPow(vecType<T, P> const & x, vecType<T, P> const & y)
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{
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return exp(y * log(x));
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}
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template <typename T>
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GLM_FUNC_QUALIFIER T fastPow(T x, int y)
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{
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T f = static_cast<T>(1);
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for(int i = 0; i < y; ++i)
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f *= x;
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return f;
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}
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template <typename T, precision P, template <typename, precision> class vecType>
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GLM_FUNC_QUALIFIER vecType<T, P> fastPow(vecType<T, P> const & x, vecType<int, P> const & y)
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{
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vecType<T, P> Result(uninitialize);
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for(length_t i = 0, n = x.length(); i < n; ++i)
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Result[i] = fastPow(x[i], y[i]);
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return Result;
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}
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// fastExp
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// Note: This function provides accurate results only for value between -1 and 1, else avoid it.
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template <typename T>
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GLM_FUNC_QUALIFIER T fastExp(T x)
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{
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// This has a better looking and same performance in release mode than the following code. However, in debug mode it's slower.
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// return 1.0f + x * (1.0f + x * 0.5f * (1.0f + x * 0.3333333333f * (1.0f + x * 0.25 * (1.0f + x * 0.2f))));
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T x2 = x * x;
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T x3 = x2 * x;
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T x4 = x3 * x;
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T x5 = x4 * x;
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return T(1) + x + (x2 * T(0.5)) + (x3 * T(0.1666666667)) + (x4 * T(0.041666667)) + (x5 * T(0.008333333333));
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}
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/* // Try to handle all values of float... but often shower than std::exp, glm::floor and the loop kill the performance
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GLM_FUNC_QUALIFIER float fastExp(float x)
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{
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const float e = 2.718281828f;
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const float IntegerPart = floor(x);
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const float FloatPart = x - IntegerPart;
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float z = 1.f;
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for(int i = 0; i < int(IntegerPart); ++i)
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z *= e;
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const float x2 = FloatPart * FloatPart;
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const float x3 = x2 * FloatPart;
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const float x4 = x3 * FloatPart;
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const float x5 = x4 * FloatPart;
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return z * (1.0f + FloatPart + (x2 * 0.5f) + (x3 * 0.1666666667f) + (x4 * 0.041666667f) + (x5 * 0.008333333333f));
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}
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// Increase accuracy on number bigger that 1 and smaller than -1 but it's not enough for high and negative numbers
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GLM_FUNC_QUALIFIER float fastExp(float x)
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{
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// This has a better looking and same performance in release mode than the following code. However, in debug mode it's slower.
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// return 1.0f + x * (1.0f + x * 0.5f * (1.0f + x * 0.3333333333f * (1.0f + x * 0.25 * (1.0f + x * 0.2f))));
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float x2 = x * x;
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float x3 = x2 * x;
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float x4 = x3 * x;
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float x5 = x4 * x;
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float x6 = x5 * x;
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float x7 = x6 * x;
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float x8 = x7 * x;
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return 1.0f + x + (x2 * 0.5f) + (x3 * 0.1666666667f) + (x4 * 0.041666667f) + (x5 * 0.008333333333f)+ (x6 * 0.00138888888888f) + (x7 * 0.000198412698f) + (x8 * 0.0000248015873f);;
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}
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*/
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template <typename T, precision P, template <typename, precision> class vecType>
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GLM_FUNC_QUALIFIER vecType<T, P> fastExp(vecType<T, P> const & x)
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{
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return detail::functor1<T, T, P, vecType>::call(fastExp, x);
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}
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// fastLog
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template <typename genType>
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GLM_FUNC_QUALIFIER genType fastLog(genType x)
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{
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return std::log(x);
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}
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/* Slower than the VC7.1 function...
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GLM_FUNC_QUALIFIER float fastLog(float x)
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{
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float y1 = (x - 1.0f) / (x + 1.0f);
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float y2 = y1 * y1;
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return 2.0f * y1 * (1.0f + y2 * (0.3333333333f + y2 * (0.2f + y2 * 0.1428571429f)));
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}
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*/
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template <typename T, precision P, template <typename, precision> class vecType>
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GLM_FUNC_QUALIFIER vecType<T, P> fastLog(vecType<T, P> const & x)
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{
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return detail::functor1<T, T, P, vecType>::call(fastLog, x);
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}
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//fastExp2, ln2 = 0.69314718055994530941723212145818f
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template <typename genType>
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GLM_FUNC_QUALIFIER genType fastExp2(genType x)
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{
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return fastExp(0.69314718055994530941723212145818f * x);
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}
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template <typename T, precision P, template <typename, precision> class vecType>
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GLM_FUNC_QUALIFIER vecType<T, P> fastExp2(vecType<T, P> const & x)
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{
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return detail::functor1<T, T, P, vecType>::call(fastExp2, x);
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}
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// fastLog2, ln2 = 0.69314718055994530941723212145818f
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template <typename genType>
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GLM_FUNC_QUALIFIER genType fastLog2(genType x)
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{
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return fastLog(x) / 0.69314718055994530941723212145818f;
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}
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template <typename T, precision P, template <typename, precision> class vecType>
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GLM_FUNC_QUALIFIER vecType<T, P> fastLog2(vecType<T, P> const & x)
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{
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return detail::functor1<T, T, P, vecType>::call(fastLog2, x);
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}
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}//namespace glm
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