mirror of https://github.com/SixLabors/ImageSharp
James Jackson-South
9 years ago
committed by
GitHub
GitHub
128 changed files with 646 additions and 637 deletions
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// <copyright file="BufferSpan{T}.cs" company="James Jackson-South">
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// Copyright (c) James Jackson-South and contributors.
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// Licensed under the Apache License, Version 2.0.
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// </copyright>
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namespace ImageSharp |
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{ |
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using System; |
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using System.Diagnostics; |
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using System.Runtime.CompilerServices; |
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using System.Runtime.InteropServices; |
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/// <summary>
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/// Represents a contiguous region of a pinned managed array.
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/// The array is usually owned by a <see cref="Buffer{T}"/> instance.
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/// </summary>
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/// <remarks>
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/// <see cref="BufferSpan{T}"/> is very similar to corefx System.Span<T>, and we try to maintain a compatible API.
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/// There are several differences though:
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/// - It's not possible to use it with stack objects or pointers to unmanaged memory, only with managed arrays.
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/// - It's possible to retrieve a reference to the array (<see cref="Array"/>) so we can pass it to API-s like <see cref="Marshal.Copy(byte[], int, IntPtr, int)"/>
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/// - It's possible to retrieve the pinned pointer. This enables optimized (unchecked) unsafe operations.
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/// - There is no bounds checking for performance reasons, only in debug mode. This makes <see cref="BufferSpan{T}"/> an unsafe type!
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/// </remarks>
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/// <typeparam name="T">The type of elements of the array</typeparam>
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internal unsafe struct BufferSpan<T> |
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where T : struct |
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{ |
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/// <summary>
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/// Initializes a new instance of the <see cref="BufferSpan{T}"/> struct from a pinned array and an start.
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/// </summary>
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/// <param name="array">The pinned array</param>
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/// <param name="start">The index at which to begin the span.</param>
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/// <param name="length">The length</param>
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[MethodImpl(MethodImplOptions.AggressiveInlining)] |
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public BufferSpan(T[] array, int start, int length) |
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{ |
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GuardArray(array); |
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DebugGuard.MustBeLessThanOrEqualTo(start, array.Length, nameof(start)); |
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DebugGuard.MustBeLessThanOrEqualTo(length, array.Length - start, nameof(length)); |
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this.Array = array; |
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this.Length = length; |
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this.Start = start; |
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} |
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/// <summary>
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/// Initializes a new instance of the <see cref="BufferSpan{T}"/> struct from a pinned array and an start.
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/// </summary>
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/// <param name="array">The pinned array</param>
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/// <param name="start">The index at which to begin the span.</param>
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[MethodImpl(MethodImplOptions.AggressiveInlining)] |
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public BufferSpan(T[] array, int start) |
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{ |
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GuardArray(array); |
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DebugGuard.MustBeLessThanOrEqualTo(start, array.Length, nameof(start)); |
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this.Array = array; |
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this.Length = array.Length - start; |
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this.Start = start; |
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} |
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/// <summary>
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/// Initializes a new instance of the <see cref="BufferSpan{T}"/> struct from a pinned array.
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/// </summary>
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/// <param name="array">The pinned array</param>
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[MethodImpl(MethodImplOptions.AggressiveInlining)] |
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public BufferSpan(T[] array) |
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{ |
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GuardArray(array); |
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this.Array = array; |
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this.Start = 0; |
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this.Length = array.Length; |
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} |
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/// <summary>
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/// Gets the backing array.
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/// </summary>
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public T[] Array { get; private set; } |
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/// <summary>
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/// Gets the length of the <see cref="BufferSpan{T}"/>
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/// </summary>
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public int Length { get; private set; } |
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/// <summary>
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/// Gets the start inside <see cref="Array"/>
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/// </summary>
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public int Start { get; private set; } |
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/// <summary>
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/// Gets the start inside <see cref="Array"/> in bytes.
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/// </summary>
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public int ByteOffset => this.Start * Unsafe.SizeOf<T>(); |
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/// <summary>
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/// Returns a reference to specified element of the span.
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/// </summary>
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/// <param name="index">The index</param>
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/// <returns>The reference to the specified element</returns>
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public ref T this[int index] |
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{ |
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[MethodImpl(MethodImplOptions.AggressiveInlining)] |
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get |
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{ |
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DebugGuard.MustBeLessThan(index, this.Length, nameof(index)); |
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ref T startRef = ref this.DangerousGetPinnableReference(); |
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return ref Unsafe.Add(ref startRef, index); |
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} |
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} |
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/// <summary>
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/// Converts generic <see cref="BufferSpan{T}"/> to a <see cref="BufferSpan{T}"/> of bytes
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/// setting it's <see cref="Start"/> and <see cref="Length"/> to correct values.
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/// </summary>
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/// <returns>The span of bytes</returns>
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[MethodImpl(MethodImplOptions.AggressiveInlining)] |
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public BufferSpan<byte> AsBytes() |
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{ |
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BufferSpan<byte> result = default(BufferSpan<byte>); |
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result.Array = Unsafe.As<byte[]>(this.Array); |
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result.Start = this.Start * Unsafe.SizeOf<T>(); |
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result.Length = this.Length * Unsafe.SizeOf<T>(); |
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return result; |
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} |
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/// <summary>
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/// Returns a reference to the 0th element of the Span. If the Span is empty, returns a reference to the location where the 0th element
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/// would have been stored. Such a reference can be used for pinning but must never be dereferenced.
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/// </summary>
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/// <returns>The reference to the 0th element</returns>
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[MethodImpl(MethodImplOptions.AggressiveInlining)] |
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public ref T DangerousGetPinnableReference() |
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{ |
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ref T origin = ref this.Array[0]; |
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return ref Unsafe.Add(ref origin, this.Start); |
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} |
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/// <summary>
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/// Forms a slice out of the given BufferSpan, beginning at 'start'.
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/// </summary>
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/// <param name="start">TThe index at which to begin this slice.</param>
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/// <returns>The offseted (sliced) BufferSpan</returns>
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[MethodImpl(MethodImplOptions.AggressiveInlining)] |
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public BufferSpan<T> Slice(int start) |
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{ |
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DebugGuard.MustBeLessThan(start, this.Length, nameof(start)); |
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BufferSpan<T> result = default(BufferSpan<T>); |
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result.Array = this.Array; |
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result.Start = this.Start + start; |
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result.Length = this.Length - start; |
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return result; |
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} |
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/// <summary>
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/// Forms a slice out of the given BufferSpan, beginning at 'start'.
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/// </summary>
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/// <param name="start">The index at which to begin this slice.</param>
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/// <param name="length">The desired length for the slice (exclusive).</param>
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/// <returns>The sliced BufferSpan</returns>
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[MethodImpl(MethodImplOptions.AggressiveInlining)] |
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public BufferSpan<T> Slice(int start, int length) |
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{ |
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DebugGuard.MustBeLessThanOrEqualTo(start, this.Length, nameof(start)); |
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DebugGuard.MustBeLessThanOrEqualTo(length, this.Length - start, nameof(length)); |
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BufferSpan<T> result = default(BufferSpan<T>); |
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result.Array = this.Array; |
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result.Start = this.Start + start; |
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result.Length = length; |
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return result; |
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} |
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/// <summary>
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/// Clears `count` elements from the beginning of the span.
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/// </summary>
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/// <param name="count">The number of elements to clear</param>
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[MethodImpl(MethodImplOptions.AggressiveInlining)] |
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public void Clear(int count) |
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{ |
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DebugGuard.MustBeLessThanOrEqualTo(count, this.Length, nameof(count)); |
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// TODO: Use Unsafe.InitBlock(ref T) for small arrays, when it get's official
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System.Array.Clear(this.Array, this.Start, count); |
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} |
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/// <summary>
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/// Clears the the span
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/// </summary>
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[MethodImpl(MethodImplOptions.AggressiveInlining)] |
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public void Clear() |
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{ |
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this.Clear(this.Length); |
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} |
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[Conditional("DEBUG")] |
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private static void GuardArray(T[] array) |
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{ |
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DebugGuard.NotNull(array, nameof(array)); |
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} |
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} |
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} |
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