gammaLog2_inl.h

Go to the documentation of this file.

namespace gum {

  ALWAYS_INLINE double GammaLog2::gammaLog2(double x) const {
    if (x <= 0)
      GUM_ERROR(OutOfBounds,
                "log2(gamma()) should be called with a positive argument");

    // if x is small, use precomputed values
    if (x < 50) {
      if (__requires_precision) {
        Idx index = int(x * 100);
        return __small_values[index]
               + (__small_values[index + 1] - __small_values[index])
                    * double(x * 100 - index);
      } else {
        Idx index = int(x * 100 + 0.5);
        return __small_values[index];
      }
    }

    // returns the approximation by the stirling formula
    return (__log_sqrt_2pi + (x - 0.5f) * log(x) - x + log(1.0 + 1.0 / (12 * x)))
           * __1log2;
  }

  ALWAYS_INLINE double GammaLog2::operator()(double x) const {
    return gammaLog2(x);
  }

  INLINE void GammaLog2::setPrecision(bool prec) { __requires_precision = prec; }

} /* namespace gum */