public static IComparer <string> For(int startIndex)
{
if (!_comparers.TryGetValue(startIndex, out var comparer))
{
comparer = new StaticStringDictionaryComparer(startIndex);
_comparers.Add(startIndex, comparer);
}
return(comparer);
}
static Expression SwitchOnChar <T>(ParameterExpression keyParameter, Expression defaultExpr, SwitchCase <T>[] switchCases, int index, int lower, int upper)
{
if (lower == upper)
{
return(Expression.Condition(
Expression.Call(_stringEquals, keyParameter, Expression.Constant(switchCases[lower].Key)),
Expression.Convert(Expression.Constant(switchCases[lower].Value), typeof(T)), defaultExpr));
}
if (index == switchCases[upper].Key.Length)
{
return(null);
}
switchCases = switchCases.Skip(lower).Take(upper - lower + 1)
.OrderBy(switchCase => switchCase.Key, StaticStringDictionaryComparer.For(index)).ToArray();
upper = upper - lower;
lower = 0;
var middle = MidPoint(lower, upper);
if (switchCases[lower].Key[index] == switchCases[middle].Key[index])
{
var result = SwitchOnChar(keyParameter, defaultExpr, switchCases, index + 1, lower, upper);
if (result != null)
{
return(result);
}
}
middle = GetIndexOfFirstDifferentCaseFromUp(switchCases, lower, middle, upper, switchCase => switchCase.Key[index]);
if (middle == -1)
{
return(null);
}
var trueBranch = SwitchOnChar(keyParameter, defaultExpr, switchCases, index, lower, middle);
if (trueBranch == null)
{
return(null);
}
var falseBranch = SwitchOnChar(keyParameter, defaultExpr, switchCases, index, middle + 1, upper);
if (falseBranch == null)
{
return(null);
}
return(Expression.Condition(
Expression.LessThan(Expression.Call(keyParameter, _stringIndex, Expression.Constant(index)),
Expression.Constant(switchCases[middle + 1].Key[index])),
trueBranch,
falseBranch));
}
