/// <summary>
/// 生成指定类型的 Switch 代码块，使用 Hash 匹配算法。
/// </summary>
/// <typeparam name="T">指定类型</typeparam>
/// <param name="ilGen">ILGenerator IL 指令生成器</param>
/// <param name="emitLoadValue">生成加载 Switch 参数的指令的委托</param>
/// <param name="comparer">哈希比较器</param>
/// <param name="cases">case 标签块集合</param>
/// <param name="defaultLabel">默认标签块</param>
/// <param name="emitLoadItem">生成加载指定 Case 块值的指定的委托</param>
public static void HashSwitch <T>(this ILGenerator ilGen,
Action <ILGenerator> emitLoadValue,
Action <ILGenerator, T> emitLoadItem,
IHashComparer <T> comparer,
CaseInfo <T>[] cases,
Label defaultLabel)
{
cases = (CaseInfo <T>[])cases.Clone();
foreach (var item in cases)
{
item.HashCode = comparer.GetHashCode(item.Value);
}
Array.Sort(cases);
var groupedCases = new Dictionary <int, List <CaseInfo <T> > >();
foreach (var item in cases)
{
groupedCases.TryGetValue(item.HashCode, out var items);
if (items is null)
{
items = new List <CaseInfo <T> >
{
item
};
groupedCases.Add(item.HashCode, items);
}
else
{
items.Add(item);
}
}
var hashCodeLocal = ilGen.DeclareLocal(typeof(int));
emitLoadValue(ilGen);
comparer.EmitGetHashCode(ilGen);
ilGen.StoreLocal(hashCodeLocal);
SwitchObject(
ilGen,
emitLoadValue,
il => il.LoadLocal(hashCodeLocal),
emitLoadItem,
comparer,
groupedCases.ToList(),
defaultLabel,
0,
(groupedCases.Count - 1) / 2,
groupedCases.Count - 1);
}
private static void SwitchObject <T>(this ILGenerator ilGen,
Action <ILGenerator> emitLoadValue,
Action <ILGenerator> emitLoadHashCode,
Action <ILGenerator, T> emitLoadItem,
IHashComparer <T> comparer,
List <KeyValuePair <int, List <CaseInfo <T> > > > cases,
Label defaultLabel,
int begin,
int index,
int end)
{
if (begin > end)
{
return;
}
if (begin == end)
{
emitLoadHashCode(ilGen);
ilGen.LoadConstant(cases[begin].Key);
ilGen.BranchIfNotEqualUnsigned(defaultLabel);
if (SwitchDoNotVerify && cases[begin].Value.Count == 1)
{
ilGen.Branch(cases[begin].Value[0].Label);
}
else
{
foreach (var item in cases[begin].Value)
{
emitLoadValue(ilGen);
emitLoadItem(ilGen, item.Value);
comparer.EmitEquals(ilGen);
ilGen.BranchTrue(item.Label);
}
}
ilGen.Branch(defaultLabel);
return;
}
if (begin + 1 == end)
{
var endLabel = ilGen.DefineLabel();
emitLoadHashCode(ilGen);
ilGen.LoadConstant(cases[begin].Key);
ilGen.BranchIfNotEqualUnsigned(endLabel);
if (SwitchDoNotVerify && cases[begin].Value.Count == 1)
{
ilGen.Branch(cases[begin].Value[0].Label);
}
else
{
foreach (var item in cases[begin].Value)
{
emitLoadValue(ilGen);
emitLoadItem(ilGen, item.Value);
comparer.EmitEquals(ilGen);
ilGen.BranchTrue(item.Label);
}
}
ilGen.MarkLabel(endLabel);
emitLoadHashCode(ilGen);
ilGen.LoadConstant(cases[end].Key);
ilGen.BranchIfNotEqualUnsigned(defaultLabel);
if (SwitchDoNotVerify && cases[end].Value.Count == 1)
{
ilGen.Branch(cases[end].Value[0].Label);
}
else
{
foreach (var item in cases[end].Value)
{
emitLoadValue(ilGen);
emitLoadItem(ilGen, item.Value);
comparer.EmitEquals(ilGen);
ilGen.BranchTrue(item.Label);
}
}
ilGen.Branch(defaultLabel);
return;
}
var greaterLabel = ilGen.DefineLabel();
emitLoadHashCode(ilGen);
ilGen.LoadConstant(cases[index].Key);
ilGen.BranchIfGreater(greaterLabel);
SwitchObject(
ilGen,
emitLoadValue,
emitLoadHashCode,
emitLoadItem,
comparer,
cases,
defaultLabel,
begin,
(begin + index) / 2,
index);
ilGen.MarkLabel(greaterLabel);
SwitchObject(
ilGen,
emitLoadValue,
emitLoadHashCode,
emitLoadItem,
comparer,
cases,
defaultLabel,
index + 1,
(index + 1 + end) / 2,
end);
}
