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Reduced allocations in ArrayBuilder #63

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merged 2 commits into from
Nov 25, 2021
Merged

Reduced allocations in ArrayBuilder #63

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013a89a
Reduced allocations in ArrayBuilder
gfoidl Nov 25, 2021
4da7514
Fixed nullability error
gfoidl Nov 25, 2021
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23 changes: 12 additions & 11 deletions source/gfoidl.DataCompression/Builders/ArrayBuilder.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -17,21 +17,21 @@ internal struct ArrayBuilder<T> : ICollectionBuilder<T>
{
private const int StartCapacity = 4;
private const int ResizeThreshold = 8;
private readonly int _maxCapacity;
private readonly List<T[]> _buffers;
private readonly int _maxCapacity;

private T[] _firstBuffer;
private T[] _currentBuffer;
private int _index;
private int _count;
private List<T[]>? _buffers;
private T[] _firstBuffer;
private T[] _currentBuffer;
private int _index;
private int _count;
//---------------------------------------------------------------------
public ArrayBuilder(bool initialize) : this(int.MaxValue) { }
//---------------------------------------------------------------------
public ArrayBuilder(int maxCapacity) : this()
{
_maxCapacity = maxCapacity;
_firstBuffer = _currentBuffer = new T[StartCapacity];
_buffers = new List<T[]>();
_buffers = null;
}
//---------------------------------------------------------------------
public readonly int Count => _count;
Expand Down Expand Up @@ -104,8 +104,8 @@ private void AddRange(T[] array)
[MethodImpl(MethodImplOptions.NoInlining)]
private void AddWithBufferAllocation(T item, ref T[] destination, ref int index)
{
_count += index - _index;
_index = index;
_count += index - _index;
_index = index;
this.AllocateBuffer();
destination = _currentBuffer;
index = _index;
Expand Down Expand Up @@ -160,7 +160,7 @@ private void AllocateBuffer()
int newCapacity = Math.Min(_count == 0 ? StartCapacity : _count * 2, _maxCapacity);
_currentBuffer = new T[newCapacity];
Array.Copy(_firstBuffer, 0, _currentBuffer, 0, _count);
_firstBuffer = _currentBuffer;
_firstBuffer = _currentBuffer;
}
else
{
Expand All @@ -175,6 +175,7 @@ private void AllocateBuffer()
// doing min(64, 100 - 64). The lhs represents double the last buffer,
// the rhs the limit minus the amount we've already allocated.

_buffers ??= new List<T[]>();
_buffers.Add(_currentBuffer);
newCapacity = Math.Min(_count, _maxCapacity - _count);
}
Expand All @@ -188,7 +189,7 @@ private readonly T[] GetBuffer(int index)
{
return index == 0
? _firstBuffer
: index <= _buffers.Count
: index <= _buffers?.Count
? _buffers[index - 1] // first "buffer" is _firstBuffer resized
: _currentBuffer;
}
Expand Down
6 changes: 3 additions & 3 deletions source/gfoidl.DataCompression/DataPointIndexedIterator.cs
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Expand Up @@ -60,7 +60,7 @@ public override bool MoveNext()
_incomingIndex = 1;
return true;
case 1:
TList source = _list;
TList source = _list!;
int snapShotIndex = _snapShotIndex;
int incomingIndex = _incomingIndex;
int lastArchivedIndex = _lastArchivedIndex;
Expand Down Expand Up @@ -132,7 +132,7 @@ public override DataPoint[] ToArray()
{
Debug.Assert(_list is not null);

TList source = _list;
TList source = _list!;

Debug.Assert(source.Count > 0);
if (source.Count == 1 && 0 < (uint)source.Count)
Expand All @@ -148,7 +148,7 @@ public override List<DataPoint> ToList()
{
Debug.Assert(_list is not null);

TList source = _list;
TList source = _list!;

Debug.Assert(source.Count > 0);
if (source.Count == 1 && 0 < (uint)source.Count)
Expand Down
4 changes: 3 additions & 1 deletion tests/gfoidl.DataCompression.Tests/Builders/ArrayBuilderTests/Add.cs
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Original file line number Diff line number Diff line change
@@ -1,4 +1,4 @@
// (c) gfoidl, all rights reserved
// (c) gfoidl, all rights reserved

using System.Collections.Generic;
using gfoidl.DataCompression.Builders;
Expand Down Expand Up @@ -32,7 +32,9 @@ private static IEnumerable<TestCaseData> Add_items_ToArray___correct_result_Test
yield return new TestCaseData(1);
yield return new TestCaseData(2);
yield return new TestCaseData(4);
yield return new TestCaseData(5); // StartCapacity + 1
yield return new TestCaseData(8);
yield return new TestCaseData(9); // ResizeThreshold + 1
yield return new TestCaseData(16);
yield return new TestCaseData(100);
yield return new TestCaseData(1_000);
Expand Down