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// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.
// See the LICENSE file in the project root for more information.
using System.Diagnostics;
using System.Runtime.CompilerServices;
using System.Runtime.Versioning;
using EditorBrowsableAttribute = System.ComponentModel.EditorBrowsableAttribute;
using EditorBrowsableState = System.ComponentModel.EditorBrowsableState;
using Internal.Runtime.CompilerServices;
#pragma warning disable 0809 //warning CS0809: Obsolete member 'Span<T>.Equals(object)' overrides non-obsolete member 'object.Equals(object)'
#if BIT64
using nuint = System.UInt64;
#else
using nuint = System.UInt32;
#endif
namespace System
{
/// <summary>
/// Span represents a contiguous region of arbitrary memory. Unlike arrays, it can point to either managed
/// or native memory, or to memory allocated on the stack. It is type- and memory-safe.
/// </summary>
[NonVersionable]
public readonly ref partial struct Span<T>
{
/// <summary>A byref or a native ptr.</summary>
internal readonly ByReference<T> _pointer;
/// <summary>The number of elements this Span contains.</summary>
#if PROJECTN
[Bound]
#endif
private readonly int _length;
/// <summary>
/// Creates a new span over the entirety of the target array.
/// </summary>
/// <param name="array">The target array.</param>
/// <remarks>Returns default when <paramref name="array"/> is null.</remarks>
/// <exception cref="System.ArrayTypeMismatchException">Thrown when <paramref name="array"/> is covariant and array's type is not exactly T[].</exception>
[MethodImpl(MethodImplOptions.AggressiveInlining)]
public Span(T[] array)
{
if (array == null)
{
this = default;
return; // returns default
}
if (default(T) == null && array.GetType() != typeof(T[]))
ThrowHelper.ThrowArrayTypeMismatchException();
_pointer = new ByReference<T>(ref Unsafe.As<byte, T>(ref array.GetRawSzArrayData()));
_length = array.Length;
}
/// <summary>
/// Creates a new span over the portion of the target array beginning
/// at 'start' index and ending at 'end' index (exclusive).
/// </summary>
/// <param name="array">The target array.</param>
/// <param name="start">The index at which to begin the span.</param>
/// <param name="length">The number of items in the span.</param>
/// <remarks>Returns default when <paramref name="array"/> is null.</remarks>
/// <exception cref="System.ArrayTypeMismatchException">Thrown when <paramref name="array"/> is covariant and array's type is not exactly T[].</exception>
/// <exception cref="System.ArgumentOutOfRangeException">
/// Thrown when the specified <paramref name="start"/> or end index is not in the range (&lt;0 or &gt;=Length).
/// </exception>
[MethodImpl(MethodImplOptions.AggressiveInlining)]
public Span(T[] array, int start, int length)
{
if (array == null)
{
if (start != 0 || length != 0)
ThrowHelper.ThrowArgumentOutOfRangeException();
this = default;
return; // returns default
}
if (default(T) == null && array.GetType() != typeof(T[]))
ThrowHelper.ThrowArrayTypeMismatchException();
#if BIT64
// See comment in Span<T>.Slice for how this works.
if ((ulong)(uint)start + (ulong)(uint)length > (ulong)(uint)array.Length)
ThrowHelper.ThrowArgumentOutOfRangeException();
#else
if ((uint)start > (uint)array.Length || (uint)length > (uint)(array.Length - start))
ThrowHelper.ThrowArgumentOutOfRangeException();
#endif
_pointer = new ByReference<T>(ref Unsafe.Add(ref Unsafe.As<byte, T>(ref array.GetRawSzArrayData()), start));
_length = length;
}
/// <summary>
/// Creates a new span over the target unmanaged buffer. Clearly this
/// is quite dangerous, because we are creating arbitrarily typed T's
/// out of a void*-typed block of memory. And the length is not checked.
/// But if this creation is correct, then all subsequent uses are correct.
/// </summary>
/// <param name="pointer">An unmanaged pointer to memory.</param>
/// <param name="length">The number of <typeparamref name="T"/> elements the memory contains.</param>
/// <exception cref="System.ArgumentException">
/// Thrown when <typeparamref name="T"/> is reference type or contains pointers and hence cannot be stored in unmanaged memory.
/// </exception>
/// <exception cref="System.ArgumentOutOfRangeException">
/// Thrown when the specified <paramref name="length"/> is negative.
/// </exception>
[CLSCompliant(false)]
[MethodImpl(MethodImplOptions.AggressiveInlining)]
public unsafe Span(void* pointer, int length)
{
if (RuntimeHelpers.IsReferenceOrContainsReferences<T>())
ThrowHelper.ThrowInvalidTypeWithPointersNotSupported(typeof(T));
if (length < 0)
ThrowHelper.ThrowArgumentOutOfRangeException();
_pointer = new ByReference<T>(ref Unsafe.As<byte, T>(ref *(byte*)pointer));
_length = length;
}
// Constructor for internal use only.
[MethodImpl(MethodImplOptions.AggressiveInlining)]
internal Span(ref T ptr, int length)
{
Debug.Assert(length >= 0);
_pointer = new ByReference<T>(ref ptr);
_length = length;
}
/// <summary>
/// Returns a reference to specified element of the Span.
/// </summary>
/// <param name="index"></param>
/// <returns></returns>
/// <exception cref="System.IndexOutOfRangeException">
/// Thrown when index less than 0 or index greater than or equal to Length
/// </exception>
public ref T this[int index]
{
#if PROJECTN
[BoundsChecking]
get
{
return ref Unsafe.Add(ref _pointer.Value, index);
}
#else
[Intrinsic]
[MethodImpl(MethodImplOptions.AggressiveInlining)]
[NonVersionable]
get
{
if ((uint)index >= (uint)_length)
ThrowHelper.ThrowIndexOutOfRangeException();
return ref Unsafe.Add(ref _pointer.Value, index);
}
#endif
}
public ref T this[Index index]
{
get
{
// Evaluate the actual index first because it helps performance
int actualIndex = index.FromEnd ? _length - index.Value : index.Value;
return ref this [actualIndex];
}
}
public Span<T> this[Range range]
{
get
{
int start = range.Start.FromEnd ? _length - range.Start.Value : range.Start.Value;
int end = range.End.FromEnd ? _length - range.End.Value : range.End.Value;
return Slice(start, end - start);
}
}
/// <summary>
/// Returns a reference to the 0th element of the Span. If the Span is empty, returns null reference.
/// It can be used for pinning and is required to support the use of span within a fixed statement.
/// </summary>
[EditorBrowsable(EditorBrowsableState.Never)]
public unsafe ref T GetPinnableReference()
{
// Ensure that the native code has just one forward branch that is predicted-not-taken.
ref T ret = ref Unsafe.AsRef<T>(null);
if (_length != 0) ret = ref _pointer.Value;
return ref ret;
}
/// <summary>
/// Clears the contents of this span.
/// </summary>
[MethodImpl(MethodImplOptions.AggressiveInlining)]
public void Clear()
{
if (RuntimeHelpers.IsReferenceOrContainsReferences<T>())
{
SpanHelpers.ClearWithReferences(ref Unsafe.As<T, IntPtr>(ref _pointer.Value), (nuint)_length * (nuint)(Unsafe.SizeOf<T>() / sizeof(nuint)));
}
else
{
SpanHelpers.ClearWithoutReferences(ref Unsafe.As<T, byte>(ref _pointer.Value), (nuint)_length * (nuint)Unsafe.SizeOf<T>());
}
}
/// <summary>
/// Fills the contents of this span with the given value.
/// </summary>
public void Fill(T value)
{
if (Unsafe.SizeOf<T>() == 1)
{
uint length = (uint)_length;
if (length == 0)
return;
T tmp = value; // Avoid taking address of the "value" argument. It would regress performance of the loop below.
Unsafe.InitBlockUnaligned(ref Unsafe.As<T, byte>(ref _pointer.Value), Unsafe.As<T, byte>(ref tmp), length);
}
else
{
// Do all math as nuint to avoid unnecessary 64->32->64 bit integer truncations
nuint length = (uint)_length;
if (length == 0)
return;
ref T r = ref _pointer.Value;
// TODO: Create block fill for value types of power of two sizes e.g. 2,4,8,16
nuint elementSize = (uint)Unsafe.SizeOf<T>();
nuint i = 0;
for (; i < (length & ~(nuint)7); i += 8)
{
Unsafe.AddByteOffset<T>(ref r, (i + 0) * elementSize) = value;
Unsafe.AddByteOffset<T>(ref r, (i + 1) * elementSize) = value;
Unsafe.AddByteOffset<T>(ref r, (i + 2) * elementSize) = value;
Unsafe.AddByteOffset<T>(ref r, (i + 3) * elementSize) = value;
Unsafe.AddByteOffset<T>(ref r, (i + 4) * elementSize) = value;
Unsafe.AddByteOffset<T>(ref r, (i + 5) * elementSize) = value;
Unsafe.AddByteOffset<T>(ref r, (i + 6) * elementSize) = value;
Unsafe.AddByteOffset<T>(ref r, (i + 7) * elementSize) = value;
}
if (i < (length & ~(nuint)3))
{
Unsafe.AddByteOffset<T>(ref r, (i + 0) * elementSize) = value;
Unsafe.AddByteOffset<T>(ref r, (i + 1) * elementSize) = value;
Unsafe.AddByteOffset<T>(ref r, (i + 2) * elementSize) = value;
Unsafe.AddByteOffset<T>(ref r, (i + 3) * elementSize) = value;
i += 4;
}
for (; i < length; i++)
{
Unsafe.AddByteOffset<T>(ref r, i * elementSize) = value;
}
}
}
/// <summary>
/// Copies the contents of this span into destination span. If the source
/// and destinations overlap, this method behaves as if the original values in
/// a temporary location before the destination is overwritten.
/// </summary>
/// <param name="destination">The span to copy items into.</param>
/// <exception cref="System.ArgumentException">
/// Thrown when the destination Span is shorter than the source Span.
/// </exception>
[MethodImpl(MethodImplOptions.AggressiveInlining)]
public void CopyTo(Span<T> destination)
{
// Using "if (!TryCopyTo(...))" results in two branches: one for the length
// check, and one for the result of TryCopyTo. Since these checks are equivalent,
// we can optimize by performing the check once ourselves then calling Memmove directly.
if ((uint)_length <= (uint)destination.Length)
{
Buffer.Memmove(ref destination._pointer.Value, ref _pointer.Value, (nuint)_length);
}
else
{
ThrowHelper.ThrowArgumentException_DestinationTooShort();
}
}
/// <summary>
/// Copies the contents of this span into destination span. If the source
/// and destinations overlap, this method behaves as if the original values in
/// a temporary location before the destination is overwritten.
/// </summary>
/// <param name="destination">The span to copy items into.</param>
/// <returns>If the destination span is shorter than the source span, this method
/// return false and no data is written to the destination.</returns>
public bool TryCopyTo(Span<T> destination)
{
bool retVal = false;
if ((uint)_length <= (uint)destination.Length)
{
Buffer.Memmove(ref destination._pointer.Value, ref _pointer.Value, (nuint)_length);
retVal = true;
}
return retVal;
}
/// <summary>
/// Returns true if left and right point at the same memory and have the same length. Note that
/// this does *not* check to see if the *contents* are equal.
/// </summary>
public static bool operator ==(Span<T> left, Span<T> right)
{
return left._length == right._length && Unsafe.AreSame<T>(ref left._pointer.Value, ref right._pointer.Value);
}
/// <summary>
/// Defines an implicit conversion of a <see cref="Span{T}"/> to a <see cref="ReadOnlySpan{T}"/>
/// </summary>
public static implicit operator ReadOnlySpan<T>(Span<T> span) => new ReadOnlySpan<T>(ref span._pointer.Value, span._length);
/// <summary>
/// For <see cref="Span{Char}"/>, returns a new instance of string that represents the characters pointed to by the span.
/// Otherwise, returns a <see cref="string"/> with the name of the type and the number of elements.
/// </summary>
public override string ToString()
{
if (typeof(T) == typeof(char))
{
unsafe
{
fixed (char* src = &Unsafe.As<T, char>(ref _pointer.Value))
return new string(src, 0, _length);
}
}
return string.Format("System.Span<{0}>[{1}]", typeof(T).Name, _length);
}
/// <summary>
/// Forms a slice out of the given span, beginning at 'start'.
/// </summary>
/// <param name="start">The index at which to begin this slice.</param>
/// <exception cref="System.ArgumentOutOfRangeException">
/// Thrown when the specified <paramref name="start"/> index is not in range (&lt;0 or &gt;=Length).
/// </exception>
[MethodImpl(MethodImplOptions.AggressiveInlining)]
public Span<T> Slice(int start)
{
if ((uint)start > (uint)_length)
ThrowHelper.ThrowArgumentOutOfRangeException();
return new Span<T>(ref Unsafe.Add(ref _pointer.Value, start), _length - start);
}
/// <summary>
/// Forms a slice out of the given span, beginning at 'start', of given length
/// </summary>
/// <param name="start">The index at which to begin this slice.</param>
/// <param name="length">The desired length for the slice (exclusive).</param>
/// <exception cref="System.ArgumentOutOfRangeException">
/// Thrown when the specified <paramref name="start"/> or end index is not in range (&lt;0 or &gt;=Length).
/// </exception>
[MethodImpl(MethodImplOptions.AggressiveInlining)]
public Span<T> Slice(int start, int length)
{
#if BIT64
// Since start and length are both 32-bit, their sum can be computed across a 64-bit domain
// without loss of fidelity. The cast to uint before the cast to ulong ensures that the
// extension from 32- to 64-bit is zero-extending rather than sign-extending. The end result
// of this is that if either input is negative or if the input sum overflows past Int32.MaxValue,
// that information is captured correctly in the comparison against the backing _length field.
// We don't use this same mechanism in a 32-bit process due to the overhead of 64-bit arithmetic.
if ((ulong)(uint)start + (ulong)(uint)length > (ulong)(uint)_length)
ThrowHelper.ThrowArgumentOutOfRangeException();
#else
if ((uint)start > (uint)_length || (uint)length > (uint)(_length - start))
ThrowHelper.ThrowArgumentOutOfRangeException();
#endif
return new Span<T>(ref Unsafe.Add(ref _pointer.Value, start), length);
}
/// <summary>
/// Copies the contents of this span into a new array. This heap
/// allocates, so should generally be avoided, however it is sometimes
/// necessary to bridge the gap with APIs written in terms of arrays.
/// </summary>
[MethodImpl(MethodImplOptions.AggressiveInlining)]
public T[] ToArray()
{
if (_length == 0)
return Array.Empty<T>();
var destination = new T[_length];
Buffer.Memmove(ref Unsafe.As<byte, T>(ref destination.GetRawSzArrayData()), ref _pointer.Value, (nuint)_length);
return destination;
}
}
}