protected virtual void _Generate(AstNodeStmSwitch Switch)
{
var allCaseValues = Switch.Cases.Select(Case => Case.CaseValue);
var caseValues = allCaseValues as IList <object> ?? allCaseValues.ToList();
if (caseValues.Count != caseValues.Distinct().Count())
{
throw new Exception("Repeated case in switch!");
}
// Check types and unique values.
var endCasesLabel = AstLabel.CreateLabel("EndCasesLabel");
var defaultLabel = AstLabel.CreateLabel("DefaultLabel");
if (Switch.Cases.Length > 0)
{
var commonType = Switch.Cases.First().CaseValue.GetType();
if (Switch.Cases.Any(Case => Case.CaseValue.GetType() != commonType))
{
throw new Exception("All cases should have the same type");
}
var doneSpecialized = false;
// Specialized constant-time integer switch (if possible)
if (AstUtils.IsIntegerType(commonType))
{
var commonMin = Switch.Cases.Min(Case => AstUtils.CastType <long>(Case.CaseValue));
var commonMax = Switch.Cases.Max(Case => AstUtils.CastType <long>(Case.CaseValue));
var casesLength = commonMax - commonMin + 1;
// No processing tables greater than 4096 elements.
if (casesLength <= 4096)
{
var labels = new AstLabel[casesLength];
for (var n = 0; n < casesLength; n++)
{
labels[n] = defaultLabel;
}
foreach (var Case in Switch.Cases)
{
var realValue = AstUtils.CastType <long>(Case.CaseValue);
var offset = realValue - commonMin;
labels[offset] = AstLabel.CreateLabel("Case_" + realValue);
}
/*
* //var SwitchVarLocal = AstLocal.Create(AllCaseValues.First().GetType(), "SwitchVarLocal" + SwitchVarCount++);
* //Generate(new AstNodeStmAssign(new AstNodeExprLocal(SwitchVarLocal), Switch.SwitchValue - new AstNodeExprCast(CommonType, CommonMin)));
* //Generate(new AstNodeStmIfElse(new AstNodeExprBinop(new AstNodeExprLocal(SwitchVarLocal), "<", 0), new AstNodeStmGotoAlways(DefaultLabel)));
* //Generate(new AstNodeStmIfElse(new AstNodeExprBinop(new AstNodeExprLocal(SwitchVarLocal), ">=", CasesLength), new AstNodeStmGotoAlways(DefaultLabel)));
* //Generate(new AstNodeExprLocal(SwitchVarLocal));
*/
Generate(Switch.SwitchValue - new AstNodeExprCast(commonType, commonMin));
Emit(OpCodes.Switch, labels);
Generate(new AstNodeStmGotoAlways(defaultLabel));
foreach (var Case in Switch.Cases)
{
var realValue = AstUtils.CastType <long>(Case.CaseValue);
var offset = realValue - commonMin;
Generate(new AstNodeStmLabel(labels[offset]));
{
Generate(Case.Code);
}
Generate(new AstNodeStmGotoAlways(endCasesLabel));
}
doneSpecialized = true;
}
else
{
// TODO: find a common shift and masks for all the values to reduce CasesLength.
// TODO: On too large test cases, split them recursively in:
// if (Var < Half) { switch(Var - LowerPartMin) { ... } } else { switch(Var - Half - UpperPartMin) { ... } }
}
}
// Specialized switch for strings (checking length, then hash, then contents)
else if (commonType == typeof(string))
{
// TODO!
}
// Generic if/else
if (!doneSpecialized)
{
var switchVarLocal =
AstLocal.Create(caseValues.First().GetType(), "SwitchVarLocal" + _switchVarCount++);
Generate(new AstNodeStmAssign(new AstNodeExprLocal(switchVarLocal), Switch.SwitchValue));
//Switch.Cases
foreach (var Case in Switch.Cases)
{
var labelSkipThisCase = AstLabel.CreateLabel("LabelCase" + Case.CaseValue);
Generate(new AstNodeStmGotoIfFalse(labelSkipThisCase,
new AstNodeExprBinop(new AstNodeExprLocal(switchVarLocal), "==",
new AstNodeExprImm(Case.CaseValue))));
Generate(Case.Code);
Generate(new AstNodeStmGotoAlways(endCasesLabel));
Generate(new AstNodeStmLabel(labelSkipThisCase));
}
}
}
Generate(new AstNodeStmLabel(defaultLabel));
if (Switch.CaseDefault != null)
{
Generate(Switch.CaseDefault.Code);
}
Generate(new AstNodeStmLabel(endCasesLabel));
}