131 lines
5.1 KiB
C#
131 lines
5.1 KiB
C#
// Licensed to the .NET Foundation under one or more agreements.
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// The .NET Foundation licenses this file to you under the MIT license.
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// See the LICENSE file in the project root for more information.
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using System;
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using System.Buffers;
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using System.Runtime.CompilerServices;
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using System.Runtime.InteropServices;
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using CommunityToolkit.HighPerformance.Buffers.Internals.Interfaces;
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using RuntimeHelpers = CommunityToolkit.HighPerformance.Helpers.Internals.RuntimeHelpers;
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namespace CommunityToolkit.HighPerformance.Buffers.Internals;
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/// <summary>
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/// A custom <see cref="MemoryManager{T}"/> that casts data from a <typeparamref name="TFrom"/> array, to <typeparamref name="TTo"/> values.
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/// </summary>
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/// <typeparam name="TFrom">The source type of items to read.</typeparam>
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/// <typeparam name="TTo">The target type to cast the source items to.</typeparam>
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internal sealed class ArrayMemoryManager<TFrom, TTo> : MemoryManager<TTo>, IMemoryManager
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where TFrom : unmanaged
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where TTo : unmanaged
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{
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/// <summary>
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/// The source <typeparamref name="TFrom"/> array to read data from.
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/// </summary>
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private readonly TFrom[] array;
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/// <summary>
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/// The starting offset within <see name="array"/>.
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/// </summary>
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private readonly int offset;
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/// <summary>
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/// The original used length for <see name="array"/>.
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/// </summary>
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private readonly int length;
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/// <summary>
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/// Initializes a new instance of the <see cref="ArrayMemoryManager{TFrom, TTo}"/> class.
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/// </summary>
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/// <param name="array">The source <typeparamref name="TFrom"/> array to read data from.</param>
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/// <param name="offset">The starting offset within <paramref name="array"/>.</param>
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/// <param name="length">The original used length for <paramref name="array"/>.</param>
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public ArrayMemoryManager(TFrom[] array, int offset, int length)
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{
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this.array = array;
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this.offset = offset;
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this.length = length;
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}
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/// <inheritdoc/>
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public override Span<TTo> GetSpan()
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{
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#if NETSTANDARD2_1_OR_GREATER
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ref TFrom r0 = ref this.array.DangerousGetReferenceAt(this.offset);
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ref TTo r1 = ref Unsafe.As<TFrom, TTo>(ref r0);
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int length = RuntimeHelpers.ConvertLength<TFrom, TTo>(this.length);
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return MemoryMarshal.CreateSpan(ref r1, length);
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#else
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Span<TFrom> span = this.array.AsSpan(this.offset, this.length);
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// We rely on MemoryMarshal.Cast here to deal with calculating the effective
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// size of the new span to return. This will also make the behavior consistent
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// for users that are both using this type as well as casting spans directly.
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return MemoryMarshal.Cast<TFrom, TTo>(span);
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#endif
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}
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/// <inheritdoc/>
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public override unsafe MemoryHandle Pin(int elementIndex = 0)
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{
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if ((uint)elementIndex >= (uint)(this.length * Unsafe.SizeOf<TFrom>() / Unsafe.SizeOf<TTo>()))
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{
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ThrowArgumentOutOfRangeExceptionForInvalidIndex();
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}
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int bytePrefix = this.offset * Unsafe.SizeOf<TFrom>();
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int byteSuffix = elementIndex * Unsafe.SizeOf<TTo>();
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int byteOffset = bytePrefix + byteSuffix;
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GCHandle handle = GCHandle.Alloc(this.array, GCHandleType.Pinned);
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ref TFrom r0 = ref this.array.DangerousGetReference();
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ref byte r1 = ref Unsafe.As<TFrom, byte>(ref r0);
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ref byte r2 = ref Unsafe.Add(ref r1, byteOffset);
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void* pi = Unsafe.AsPointer(ref r2);
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return new(pi, handle);
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}
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/// <inheritdoc/>
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public override void Unpin()
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{
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}
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/// <inheritdoc/>
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protected override void Dispose(bool disposing)
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{
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}
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/// <inheritdoc/>
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public Memory<T> GetMemory<T>(int offset, int length)
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where T : unmanaged
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{
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// We need to calculate the right offset and length of the new Memory<T>. The local offset
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// is the original offset into the wrapped TFrom[] array, while the input offset is the one
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// with respect to TTo items in the Memory<TTo> instance that is currently being cast.
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int absoluteOffset = this.offset + RuntimeHelpers.ConvertLength<TTo, TFrom>(offset);
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int absoluteLength = RuntimeHelpers.ConvertLength<TTo, TFrom>(length);
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// We have a special handling in cases where the user is circling back to the original type
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// of the wrapped array. In this case we can just return a memory wrapping that array directly,
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// with offset and length being adjusted, without the memory manager indirection.
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if (typeof(T) == typeof(TFrom))
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{
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return (Memory<T>)(object)this.array.AsMemory(absoluteOffset, absoluteLength);
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}
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return new ArrayMemoryManager<TFrom, T>(this.array, absoluteOffset, absoluteLength).Memory;
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}
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/// <summary>
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/// Throws an <see cref="ArgumentOutOfRangeException"/> when the target index for <see cref="Pin"/> is invalid.
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/// </summary>
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private static void ThrowArgumentOutOfRangeExceptionForInvalidIndex()
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{
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throw new ArgumentOutOfRangeException("elementIndex", "The input index is not in the valid range");
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}
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}
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