NullableDoubleMinMaxAggregationOperator.cs source code in C# .NET

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                         / 4.0 / 4.0 / untmp / DEVDIV_TFS / Dev10 / Releases / RTMRel / ndp / fx / src / Core / System / Linq / Parallel / QueryOperators / Inlined / NullableDoubleMinMaxAggregationOperator.cs / 1305376 / NullableDoubleMinMaxAggregationOperator.cs
                        
                        
                            // ==++== 
//
//   Copyright (c) Microsoft Corporation.  All rights reserved.
//
// ==--== 
// =+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+
// 
// NullableDoubleMinMaxAggregationOperator.cs 
//
// [....] 
//
// =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-

using System.Collections.Generic; 
using System.Diagnostics.Contracts;
using System.Threading; 
 
namespace System.Linq.Parallel
{ 
    /// 
    /// An inlined min/max aggregation and its enumerator, for Nullable{Double}s.
    ///
    /// Notes: 
    ///     Note that normally double.NaN < anything is false, as is anything < NaN.  This would
    ///     lead to some strangeness in Min and Max, e.g. Min({ NaN, 5.0 } == NaN, yet 
    ///     Min({ 5.0, NaN }) == 5.0!  We impose a total ordering so that NaN is smaller than 
    ///     everything, including -infinity, which is consistent with Comparer_T.
    ///  
    internal sealed class NullableDoubleMinMaxAggregationOperator : InlinedAggregationOperator
    {
        private readonly int m_sign; // The sign (-1 for min, 1 for max).
 
        //----------------------------------------------------------------------------------------
        // Constructs a new instance of a min/max associative operator. 
        // 

        internal NullableDoubleMinMaxAggregationOperator(IEnumerable child, int sign) : base(child) 
        {
            Contract.Assert(sign == -1 || sign == 1, "invalid sign");
            m_sign = sign;
        } 

        //--------------------------------------------------------------------------------------- 
        // Executes the entire query tree, and aggregates the intermediate results into the 
        // final result based on the binary operators and final reduction.
        // 
        // Return Value:
        //     The single result of aggregation.
        //
 
        protected override double? InternalAggregate(ref Exception singularExceptionToThrow)
        { 
            // Because the final reduction is typically much cheaper than the intermediate 
            // reductions over the individual partitions, and because each parallel partition
            // will do a lot of work to produce a single output element, we prefer to turn off 
            // pipelining, and process the final reductions serially.
            using (IEnumerator enumerator = GetEnumerator(ParallelMergeOptions.FullyBuffered, true))
            {
                // Just return null right away for empty results. 
                if (!enumerator.MoveNext())
                { 
                    return null; 
                }
 
                double? best = enumerator.Current;

                // Based on the sign, do either a min or max reduction.
                if (m_sign == -1) 
                {
                    while (enumerator.MoveNext()) 
                    { 
                        double? current = enumerator.Current;
                        if (current == null) continue; 
                        if (best == null || current < best || double.IsNaN(current.GetValueOrDefault()))
                        {
                            best = current;
                        } 
                    }
                } 
                else 
                {
                    while (enumerator.MoveNext()) 
                    {
                        double? current = enumerator.Current;
                        if (current == null) continue;
                        if (best == null || current > best || double.IsNaN(best.GetValueOrDefault())) 
                        {
                            best = current; 
                        } 
                    }
                } 

                return best;
            }
        } 

        //--------------------------------------------------------------------------------------- 
        // Creates an enumerator that is used internally for the final aggregation step. 
        //
 
        protected override QueryOperatorEnumerator CreateEnumerator(
            int index, int count, QueryOperatorEnumerator source, object sharedData, CancellationToken cancellationToken)
        {
            return new NullableDoubleMinMaxAggregationOperatorEnumerator(source, index, m_sign, cancellationToken); 
        }
 
        //--------------------------------------------------------------------------------------- 
        // This enumerator type encapsulates the intermediary aggregation over the underlying
        // (possibly partitioned) data source. 
        //

        private class NullableDoubleMinMaxAggregationOperatorEnumerator : InlinedAggregationOperatorEnumerator
        { 
            private QueryOperatorEnumerator m_source; // The source data.
            private int m_sign; // The sign for comparisons (-1 means min, 1 means max). 
 
            //----------------------------------------------------------------------------------------
            // Instantiates a new aggregation operator. 
            //

            internal NullableDoubleMinMaxAggregationOperatorEnumerator(QueryOperatorEnumerator source, int partitionIndex, int sign,
                CancellationToken cancellationToken) : 
                base(partitionIndex, cancellationToken)
            { 
                Contract.Assert(source != null); 
                m_source = source;
                m_sign = sign; 
            }

            //---------------------------------------------------------------------------------------
            // Tallies up the min/max of the underlying data source, walking the entire thing the first 
            // time MoveNext is called on this object.
            // 
 
            protected override bool MoveNextCore(ref double? currentElement)
            { 
                // Based on the sign, do either a min or max reduction.
                QueryOperatorEnumerator source = m_source;
                TKey keyUnused = default(TKey);
 
                if (source.MoveNext(ref currentElement, ref keyUnused))
                { 
                    int i = 0; 
                    // We just scroll through the enumerator and find the min or max.
                    if (m_sign == -1) 
                    {
                        double? elem = default(double?);
                        while (source.MoveNext(ref elem, ref keyUnused))
                        { 
                            if ((i++ & CancellationState.POLL_INTERVAL) == 0)
                                CancellationState.ThrowIfCanceled(m_cancellationToken); 
 
                            if (elem == null) continue;
                            if (currentElement == null || elem < currentElement || double.IsNaN(elem.GetValueOrDefault())) 
                            {
                                currentElement = elem;
                            }
                        } 
                    }
                    else 
                    { 
                        double? elem = default(double?);
                        while (source.MoveNext(ref elem, ref keyUnused)) 
                        {
                            if ((i++ & CancellationState.POLL_INTERVAL) == 0)
                                CancellationState.ThrowIfCanceled(m_cancellationToken);
 
                            if (elem == null) continue;
                            if (currentElement == null || elem > currentElement || double.IsNaN(currentElement.GetValueOrDefault())) 
                            { 
                                currentElement = elem;
                            } 
                        }
                    }

                    // The sum has been calculated. Now just return. 
                    return true;
                } 
 
                return false;
            } 

            //----------------------------------------------------------------------------------------
            // Dispose of resources associated with the underlying enumerator.
            // 

            protected override void Dispose(bool disposing) 
            { 
                Contract.Assert(m_source != null);
                m_source.Dispose(); 
            }
        }
    }
} 

// File provided for Reference Use Only by Microsoft Corporation (c) 2007.
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NullableDoubleMinMaxAggregationOperator.cs source code in C# .NET

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