private double EntropyOfCond(ArraySlice <DecisionTest> S)
{
double p1;
int index = Split(S, out p1);
double p2 = 1.0 - p1;
double result = (Functions.Entropy(p1) + Functions.Entropy(1 - p1)) / platform.BranchCost;
return(result);
}
private double EntropyOfSwitch(ArraySlice <DecisionTest> S)
{
double result = 0;
foreach (var test in S)
{
result += Functions.Entropy(test.Probability);
}
result /= platform.SwitchCost;
return(result);
}
private void Normalize(ArraySlice <DecisionTest> S)
{
var tests = S.Array;
double sum = 0;
foreach (var test in S)
{
sum += test.Probability;
}
foreach (var test in S)
{
test.Probability /= sum;
}
}
private bool IsSwitchable(ArraySlice <DecisionTest> S)
{
long elementCount = S.Sum(test => test.Interval.LongSize);
if (elementCount > platform.MaxSwitchElementCount)
{
return(false);
}
var rangeSize = S[S.Count - 1].Interval.Last
- S[0].Interval.First
+ 1;
double density = elementCount / (double)rangeSize;
return(density > platform.MinSwitchDensity);
}
private Decision GenTree(ArraySlice <DecisionTest> S)
{
if (S.Count == 1)
{
return(GetActionDecision(S[0].Action));
}
Normalize(S);
if (IsSwitchable(S) && EntropyOfSwitch(S) > EntropyOfCond(S))
{
return(GenSwitch(S));
}
else
{
return(GenCond(S));
}
}
internal JumpTableDecision(ArraySlice <DecisionTest> tests, Func <int, ActionDecision> idToAction)
{
this.tests = tests;
this.startElement = tests.Array[tests.Offset].Interval.First;
int elementCount = tests.Array[tests.Offset + tests.Count - 1].Interval.Last - startElement + 1;
this.elementToAction = new Decision[elementCount];
foreach (var test in tests)
{
var action = idToAction(test.Action);
if (!leafDecisions.Contains(action))
{
leafDecisions.Add(action);
}
for (int i = test.Interval.First; i <= test.Interval.Last; ++i)
{
elementToAction[i - startElement] = action;
}
}
}
private Decision GenSwitch(ArraySlice <DecisionTest> S)
{
var result = new JumpTableDecision(S, GetActionDecision);
return(result);
}