aGrUM  0.13.2
gammaLog2_inl.h
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27 namespace gum {
28 
29  ALWAYS_INLINE double GammaLog2::gammaLog2(double x) const {
30  if (x <= 0)
32  "log2(gamma()) should be called with a positive argument");
33 
34  // if x is small, use precomputed values
35  if (x < 50) {
37  Idx index = int(x * 100);
38  return __small_values[index]
39  + (__small_values[index + 1] - __small_values[index])
40  * double(x * 100 - index);
41  } else {
42  Idx index = int(x * 100 + 0.5);
43  return __small_values[index];
44  }
45  }
46 
47  // returns the approximation by the stirling formula
48  return (__log_sqrt_2pi + (x - 0.5f) * log(x) - x + log(1.0 + 1.0 / (12 * x)))
49  * __1log2;
50  }
51 
52  ALWAYS_INLINE double GammaLog2::operator()(double x) const {
53  return gammaLog2(x);
54  }
55 
56  INLINE void GammaLog2::setPrecision(bool prec) { __requires_precision = prec; }
57 
58 } /* namespace gum */
double operator()(double x) const
Returns log2 ( gamma (x) ) for x > 0.
Definition: gammaLog2_inl.h:52
double gammaLog2(double x) const
Returns log2 ( gamma (x) ) for x >= 0.
Definition: gammaLog2_inl.h:29
void setPrecision(bool p)
Sets whether we need more precision for small values.
Definition: gammaLog2_inl.h:56
gum is the global namespace for all aGrUM entities
Definition: agrum.h:25
static constexpr double __log_sqrt_2pi
The value of std::log ( std::sqrt(2pi) ).
Definition: gammaLog2.h:118
bool __requires_precision
Indicates whether we need more precision for small values.
Definition: gammaLog2.h:112
static const std::vector< double > __small_values
The 5000 values from 0 to 50 by step of 1/100.
Definition: gammaLog2.h:121
unsigned long Idx
Type for indexes.
Definition: types.h:43
#define GUM_ERROR(type, msg)
Definition: exceptions.h:66
static constexpr double __1log2
The value of 1 / std::log(2).
Definition: gammaLog2.h:115