VariableLengthIntegerHelper.cs

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using System.Buffers.Binary;
 
namespace System.Net.Http;
 
internal static class VariableLengthIntegerHelper
{
    public static bool TryRead(ReadOnlySpan<byte> buffer, out long value, out int bytesRead)
    {
        if (buffer.Length != 0)
        {
            byte b = buffer[0];
            switch (b & 0xC0)
            {
            case 0:
                value = b;
                bytesRead = 1;
                return true;
            case 64:
            {
                if (BinaryPrimitives.TryReadUInt16BigEndian(buffer, out var value3))
                {
                    value = (uint)(value3 - 16384);
                    bytesRead = 2;
                    return true;
                }
                break;
            }
            case 128:
            {
                if (BinaryPrimitives.TryReadUInt32BigEndian(buffer, out var value4))
                {
                    value = (uint)((int)value4 - int.MinValue);
                    bytesRead = 4;
                    return true;
                }
                break;
            }
            default:
            {
                if (BinaryPrimitives.TryReadUInt64BigEndian(buffer, out var value2))
                {
                    value = (long)value2 - -4611686018427387904L;
                    bytesRead = 8;
                    return true;
                }
                break;
            }
            }
        }
        value = 0L;
        bytesRead = 0;
        return false;
    }
 
    public static bool TryWrite(Span<byte> buffer, long longToEncode, out int bytesWritten)
    {
        if (longToEncode < 63)
        {
            if (buffer.Length != 0)
            {
                buffer[0] = (byte)longToEncode;
                bytesWritten = 1;
                return true;
            }
        }
        else if (longToEncode < 16383)
        {
            if (BinaryPrimitives.TryWriteUInt16BigEndian(buffer, (ushort)((uint)(int)longToEncode | 0x4000u)))
            {
                bytesWritten = 2;
                return true;
            }
        }
        else if (longToEncode < 1073741823)
        {
            if (BinaryPrimitives.TryWriteUInt32BigEndian(buffer, (uint)(int)longToEncode | 0x80000000u))
            {
                bytesWritten = 4;
                return true;
            }
        }
        else if (BinaryPrimitives.TryWriteUInt64BigEndian(buffer, (ulong)longToEncode | 0xC000000000000000uL))
        {
            bytesWritten = 8;
            return true;
        }
        bytesWritten = 0;
        return false;
    }
 
    public static int WriteInteger(Span<byte> buffer, long longToEncode)
    {
        int bytesWritten;
        bool flag = TryWrite(buffer, longToEncode, out bytesWritten);
        return bytesWritten;
    }
 
    public static int GetByteCount(long value)
    {
        if (value >= 63)
        {
            if (value >= 16383)
            {
                if (value >= 1073741823)
                {
                    return 8;
                }
                return 4;
            }
            return 2;
        }
        return 1;
    }
}