Span factoring (#26667)

Author: tarekgh

src/Common/src/CoreLib/System/ReadOnlySpan.Fast.cs

@@ -0,0 +1,262 @@
+// 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.ComponentModel;
+using System.Diagnostics;
+using System.Runtime.CompilerServices;
+using System.Runtime.Versioning;
+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>
+    /// ReadOnlySpan 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>
+    [DebuggerTypeProxy(typeof(SpanDebugView<>))]
+    [DebuggerDisplay("{DebuggerDisplay,nq}")]
+    [NonVersionable]
+    public readonly ref partial struct ReadOnlySpan<T>
+    {
+        /// <summary>A byref or a native ptr.</summary>
+        internal readonly ByReference<T> _pointer;
+        /// <summary>The number of elements this ReadOnlySpan contains.</summary>
+#if PROJECTN
+        [Bound]
+#endif
+        private readonly int _length;
+
+        /// <summary>
+        /// Creates a new read-only span over the entirety of the target array.
+        /// </summary>
+        /// <param name="array">The target array.</param>
+        /// <exception cref="System.ArgumentNullException">Thrown when <paramref name="array"/> is a null
+        /// reference (Nothing in Visual Basic).</exception>
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        public ReadOnlySpan(T[] array)
+        {
+            if (array == null)
+                ThrowHelper.ThrowArgumentNullException(ExceptionArgument.array);
+
+            _pointer = new ByReference<T>(ref Unsafe.As<byte, T>(ref array.GetRawSzArrayData()));
+            _length = array.Length;
+        }
+
+        /// <summary>
+        /// Creates a new read-only 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 read-only span.</param>
+        /// <param name="length">The number of items in the read-only span.</param>
+        /// <exception cref="System.ArgumentNullException">Thrown when <paramref name="array"/> is a null
+        /// reference (Nothing in Visual Basic).</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 ReadOnlySpan(T[] array, int start, int length)
+        {
+            if (array == null)
+                ThrowHelper.ThrowArgumentNullException(ExceptionArgument.array);
+            if ((uint)start > (uint)array.Length || (uint)length > (uint)(array.Length - start))
+                ThrowHelper.ThrowArgumentOutOfRangeException();
+
+            _pointer = new ByReference<T>(ref Unsafe.Add(ref Unsafe.As<byte, T>(ref array.GetRawSzArrayData()), start));
+            _length = length;
+        }
+
+        /// <summary>
+        /// Creates a new read-only 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 ReadOnlySpan(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 ReadOnlySpan(ref T ptr, int length)
+        {
+            Debug.Assert(length >= 0);
+
+            _pointer = new ByReference<T>(ref ptr);
+            _length = length;
+        }
+
+        /// <summary>
+        /// Returns the specified element of the read-only 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 readonly 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
+        }
+
+        /// <summary>
+        /// Copies the contents of this read-only 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.
+        ///
+        /// <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>
+        /// </summary>
+        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();
+            }
+        }
+
+        /// Copies the contents of this read-only 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>
+        /// <returns>If the destination span is shorter than the source span, this method
+        /// return false and no data is written to the destination.</returns>
+        /// <param name="destination">The span to copy items into.</param>
+        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 ==(ReadOnlySpan<T> left, ReadOnlySpan<T> right)
+        {
+            return left._length == right._length && Unsafe.AreSame<T>(ref left._pointer.Value, ref right._pointer.Value);
+        }
+
+        /// <summary>
+        /// For <see cref="ReadOnlySpan{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.ReadOnlySpan<{0}>[{1}]", typeof(T).Name, _length);
+        }
+
+        /// <summary>
+        /// Forms a slice out of the given read-only 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 ReadOnlySpan<T> Slice(int start)
+        {
+            if ((uint)start > (uint)_length)
+                ThrowHelper.ThrowArgumentOutOfRangeException();
+
+            return new ReadOnlySpan<T>(ref Unsafe.Add(ref _pointer.Value, start), _length - start);
+        }
+
+        /// <summary>
+        /// Forms a slice out of the given read-only 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 ReadOnlySpan<T> Slice(int start, int length)
+        {
+            if ((uint)start > (uint)_length || (uint)length > (uint)(_length - start))
+                ThrowHelper.ThrowArgumentOutOfRangeException();
+
+            return new ReadOnlySpan<T>(ref Unsafe.Add(ref _pointer.Value, start), length);
+        }
+
+        /// <summary>
+        /// Copies the contents of this read-only 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>
+        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;
+        }
+    }
+}