private static GrammarNode <T> GetInnerNode(GrammarNode <T> grammarNode, ref RepetitionRange range, Boolean isLazy)
{
if (grammarNode is Repetition <T> repetition && repetition.IsLazy == isLazy)
{
/* expr{α}{β} ≡ expr{α·β} */
if (repetition.Range.IsSingleElement && range.IsSingleElement)
{
var reps = repetition.Range.Minimum * range.Minimum;
range = new RepetitionRange(reps, reps);
return(repetition.InnerNode);
}
/* expr{a, b}{c, d} ≡ expr{a·c, b·d} IF b·c ≥ a·(c + 1) - 1
* Basically checks if each occurrence of the range [n·a, n·b] where n ∈ [c, d]
* overlaps with each other.
* If it does, we then just get the range of [a·c, b·d] (the union of all
* occurrences of the range on the previous sentence) instead of nesting the repetitions.
*/
if (repetition.Range.IsFinite &&
range.IsFinite &&
repetition.Range.Maximum * range.Minimum >= repetition.Range.Minimum * (range.Minimum + 1) - 1)
{
range = new RepetitionRange(
SaturatingMath.Multiply(repetition.Range.Minimum, range.Minimum),
SaturatingMath.Multiply(repetition.Range.Maximum !.Value, range.Maximum !.Value));
return(repetition.InnerNode);
}
}
return(grammarNode);
}
/// <summary>
/// Creates a new repetition node
/// </summary>
/// <param name="grammarNode"></param>
/// <param name="range"></param>
/// <param name="isLazy"></param>
public Repetition(GrammarNode <T> grammarNode, RepetitionRange range, Boolean isLazy)
: base(GetInnerNode(grammarNode, ref range, isLazy))
{
this.Range = range;
this.IsLazy = isLazy;
}
