Update BigInteger and Complex to support UTF8 parsing and formatting (#117745)

Author: tannergooding

src/libraries/Common/src/System/Text/ValueStringBuilder_1.cs

@@ -0,0 +1,314 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using System.Buffers;
+using System.Diagnostics;
+using System.Runtime.CompilerServices;
+using System.Runtime.InteropServices;
+
+#nullable enable
+
+namespace System.Text
+{
+    internal ref partial struct ValueStringBuilder<TChar>
+        where TChar : unmanaged
+    {
+        private TChar[]? _arrayToReturnToPool;
+        private Span<TChar> _chars;
+        private int _pos;
+
+        public ValueStringBuilder(Span<TChar> initialBuffer)
+        {
+            Debug.Assert((typeof(TChar) == typeof(Utf8Char)) || (typeof(TChar) == typeof(Utf16Char)));
+
+            _arrayToReturnToPool = null;
+            _chars = initialBuffer;
+            _pos = 0;
+        }
+
+        public ValueStringBuilder(int initialCapacity)
+        {
+            Debug.Assert((typeof(TChar) == typeof(Utf8Char)) || (typeof(TChar) == typeof(Utf16Char)));
+
+            _arrayToReturnToPool = ArrayPool<TChar>.Shared.Rent(initialCapacity);
+            _chars = _arrayToReturnToPool;
+            _pos = 0;
+        }
+
+        public int Length
+        {
+            readonly get => _pos;
+            set
+            {
+                Debug.Assert(value >= 0);
+                Debug.Assert(value <= _chars.Length);
+                _pos = value;
+            }
+        }
+
+        public readonly int Capacity => _chars.Length;
+
+        public void EnsureCapacity(int capacity)
+        {
+            // This is not expected to be called this with negative capacity
+            Debug.Assert(capacity >= 0);
+
+            // If the caller has a bug and calls this with negative capacity, make sure to call Grow to throw an exception.
+            if ((uint)capacity > (uint)_chars.Length)
+                Grow(capacity - _pos);
+        }
+
+        /// <summary>
+        /// Get a pinnable reference to the builder.
+        /// Does not ensure there is a null TChar after <see cref="Length"/>
+        /// This overload is pattern matched in the C# 7.3+ compiler so you can omit
+        /// the explicit method call, and write eg "fixed (TChar* c = builder)"
+        /// </summary>
+        public readonly ref TChar GetPinnableReference()
+        {
+            return ref MemoryMarshal.GetReference(_chars);
+        }
+
+        /// <summary>
+        /// Get a pinnable reference to the builder.
+        /// </summary>
+        /// <param name="terminate">Ensures that the builder has a null TChar after <see cref="Length"/></param>
+        public ref TChar GetPinnableReference(bool terminate)
+        {
+            if (terminate)
+            {
+                EnsureCapacity(Length + 1);
+                _chars[Length] = default;
+            }
+            return ref MemoryMarshal.GetReference(_chars);
+        }
+
+        public readonly ref TChar this[int index]
+        {
+            get
+            {
+                Debug.Assert(index < _pos);
+                return ref _chars[index];
+            }
+        }
+
+        public override string ToString()
+        {
+            string result;
+            Span<TChar> slice = _chars.Slice(0, _pos);
+
+            if (typeof(TChar) == typeof(Utf8Char))
+            {
+                result = Encoding.UTF8.GetString(Unsafe.BitCast<ReadOnlySpan<TChar>, ReadOnlySpan<byte>>(slice));
+            }
+            else
+            {
+                Debug.Assert(typeof(TChar) == typeof(Utf16Char));
+                result = Unsafe.BitCast<ReadOnlySpan<TChar>, ReadOnlySpan<char>>(slice).ToString();
+            }
+
+            Dispose();
+            return result;
+        }
+
+        /// <summary>Returns the underlying storage of the builder.</summary>
+        public readonly Span<TChar> RawChars => _chars;
+
+        /// <summary>
+        /// Returns a span around the contents of the builder.
+        /// </summary>
+        /// <param name="terminate">Ensures that the builder has a null TChar after <see cref="Length"/></param>
+        public ReadOnlySpan<TChar> AsSpan(bool terminate)
+        {
+            if (terminate)
+            {
+                EnsureCapacity(Length + 1);
+                _chars[Length] = default;
+            }
+            return _chars.Slice(0, _pos);
+        }
+
+        public readonly ReadOnlySpan<TChar> AsSpan() => _chars.Slice(0, _pos);
+        public readonly ReadOnlySpan<TChar> AsSpan(int start) => _chars.Slice(start, _pos - start);
+        public readonly ReadOnlySpan<TChar> AsSpan(int start, int length) => _chars.Slice(start, length);
+
+        public bool TryCopyTo(Span<TChar> destination, out int charsWritten)
+        {
+            if (_chars.Slice(0, _pos).TryCopyTo(destination))
+            {
+                charsWritten = _pos;
+                Dispose();
+                return true;
+            }
+            else
+            {
+                charsWritten = 0;
+                Dispose();
+                return false;
+            }
+        }
+
+        public void Insert(int index, TChar value, int count)
+        {
+            if (_pos > _chars.Length - count)
+            {
+                Grow(count);
+            }
+
+            int remaining = _pos - index;
+            _chars.Slice(index, remaining).CopyTo(_chars.Slice(index + count));
+            _chars.Slice(index, count).Fill(value);
+            _pos += count;
+        }
+
+        public void Insert(int index, ReadOnlySpan<TChar> text)
+        {
+            if (text.IsEmpty)
+            {
+                return;
+            }
+
+            int count = text.Length;
+
+            if (_pos > (_chars.Length - count))
+            {
+                Grow(count);
+            }
+
+            int remaining = _pos - index;
+            _chars.Slice(index, remaining).CopyTo(_chars.Slice(index + count));
+            text.CopyTo(_chars.Slice(index));
+            _pos += count;
+        }
+
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        public void Append(TChar c)
+        {
+            int pos = _pos;
+            Span<TChar> chars = _chars;
+            if ((uint)pos < (uint)chars.Length)
+            {
+                chars[pos] = c;
+                _pos = pos + 1;
+            }
+            else
+            {
+                GrowAndAppend(c);
+            }
+        }
+
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        public void Append(ReadOnlySpan<TChar> text)
+        {
+            if (text.IsEmpty)
+            {
+                return;
+            }
+
+            int pos = _pos;
+            if (text.Length == 1 && (uint)pos < (uint)_chars.Length) // very common case, e.g. appending strings from NumberFormatInfo like separators, percent symbols, etc.
+            {
+                _chars[pos] = text[0];
+                _pos = pos + 1;
+            }
+            else
+            {
+                AppendSlow(text);
+            }
+        }
+
+        private void AppendSlow(ReadOnlySpan<TChar> text)
+        {
+            int pos = _pos;
+            if (pos > _chars.Length - text.Length)
+            {
+                Grow(text.Length);
+            }
+
+            text.CopyTo(_chars.Slice(pos));
+            _pos += text.Length;
+        }
+
+        public void Append(TChar c, int count)
+        {
+            if (_pos > _chars.Length - count)
+            {
+                Grow(count);
+            }
+
+            Span<TChar> dst = _chars.Slice(_pos, count);
+            for (int i = 0; i < dst.Length; i++)
+            {
+                dst[i] = c;
+            }
+            _pos += count;
+        }
+
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        public Span<TChar> AppendSpan(int length)
+        {
+            int origPos = _pos;
+            if (origPos > _chars.Length - length)
+            {
+                Grow(length);
+            }
+
+            _pos = origPos + length;
+            return _chars.Slice(origPos, length);
+        }
+
+        [MethodImpl(MethodImplOptions.NoInlining)]
+        private void GrowAndAppend(TChar c)
+        {
+            Grow(1);
+            Append(c);
+        }
+
+        /// <summary>
+        /// Resize the internal buffer either by doubling current buffer size or
+        /// by adding <paramref name="additionalCapacityBeyondPos"/> to
+        /// <see cref="_pos"/> whichever is greater.
+        /// </summary>
+        /// <param name="additionalCapacityBeyondPos">
+        /// Number of chars requested beyond current position.
+        /// </param>
+        [MethodImpl(MethodImplOptions.NoInlining)]
+        private void Grow(int additionalCapacityBeyondPos)
+        {
+            Debug.Assert(additionalCapacityBeyondPos > 0);
+            Debug.Assert(_pos > _chars.Length - additionalCapacityBeyondPos, "Grow called incorrectly, no resize is needed.");
+
+            const uint ArrayMaxLength = 0x7FFFFFC7; // same as Array.MaxLength
+
+            // Increase to at least the required size (_pos + additionalCapacityBeyondPos), but try
+            // to double the size if possible, bounding the doubling to not go beyond the max array length.
+            int newCapacity = (int)Math.Max(
+                (uint)(_pos + additionalCapacityBeyondPos),
+                Math.Min((uint)_chars.Length * 2, ArrayMaxLength));
+
+            // Make sure to let Rent throw an exception if the caller has a bug and the desired capacity is negative.
+            // This could also go negative if the actual required length wraps around.
+            TChar[] poolArray = ArrayPool<TChar>.Shared.Rent(newCapacity);
+
+            _chars.Slice(0, _pos).CopyTo(poolArray);
+
+            TChar[]? toReturn = _arrayToReturnToPool;
+            _chars = _arrayToReturnToPool = poolArray;
+            if (toReturn != null)
+            {
+                ArrayPool<TChar>.Shared.Return(toReturn);
+            }
+        }
+
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        public void Dispose()
+        {
+            TChar[]? toReturn = _arrayToReturnToPool;
+            this = default; // for safety, to avoid using pooled array if this instance is erroneously appended to again
+            if (toReturn != null)
+            {
+                ArrayPool<TChar>.Shared.Return(toReturn);
+            }
+        }
+    }
+}