AggregationMinMaxHelpers.cs

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using System.Collections.Generic;
using System.Linq.Parallel;
 
namespace System.Linq;
 
internal static class AggregationMinMaxHelpers<T>
{
    private static T Reduce(IEnumerable<T> source, int sign)
    {
        Func<Pair<bool, T>, T, Pair<bool, T>> intermediateReduce = MakeIntermediateReduceFunction(sign);
        Func<Pair<bool, T>, Pair<bool, T>, Pair<bool, T>> finalReduce = MakeFinalReduceFunction(sign);
        Func<Pair<bool, T>, T> resultSelector = MakeResultSelectorFunction();
        AssociativeAggregationOperator<T, Pair<bool, T>, T> associativeAggregationOperator = new AssociativeAggregationOperator<T, Pair<bool, T>, T>(source, new Pair<bool, T>(first: false, default(T)), null, seedIsSpecified: true, intermediateReduce, finalReduce, resultSelector, default(T) != null, QueryAggregationOptions.AssociativeCommutative);
        return associativeAggregationOperator.Aggregate();
    }
 
    internal static T ReduceMin(IEnumerable<T> source)
    {
        return Reduce(source, -1);
    }
 
    internal static T ReduceMax(IEnumerable<T> source)
    {
        return Reduce(source, 1);
    }
 
    private static Func<Pair<bool, T>, T, Pair<bool, T>> MakeIntermediateReduceFunction(int sign)
    {
        Comparer<T> comparer = Util.GetDefaultComparer<T>();
        return (Pair<bool, T> accumulator, T element) => ((default(T) != null || element != null) && (!accumulator.First || Util.Sign(comparer.Compare(element, accumulator.Second)) == sign)) ? new Pair<bool, T>(first: true, element) : accumulator;
    }
 
    private static Func<Pair<bool, T>, Pair<bool, T>, Pair<bool, T>> MakeFinalReduceFunction(int sign)
    {
        Comparer<T> comparer = Util.GetDefaultComparer<T>();
        return (Pair<bool, T> accumulator, Pair<bool, T> element) => (element.First && (!accumulator.First || Util.Sign(comparer.Compare(element.Second, accumulator.Second)) == sign)) ? new Pair<bool, T>(first: true, element.Second) : accumulator;
    }
 
    private static Func<Pair<bool, T>, T> MakeResultSelectorFunction()
    {
        return (Pair<bool, T> accumulator) => accumulator.Second;
    }
}