public static TransformationStatus ComputeEncodedBytesFromUtf16(ReadOnlySpan <byte> source, out int bytesNeeded)
{
bytesNeeded = 0;
// try? because Convert.ConvertToUtf32 can throw
// if the high/low surrogates aren't valid; no point
// running all the tests twice per code-point
try
{
ref char utf16 = ref Unsafe.As <byte, char>(ref source.DangerousGetPinnableReference());
int utf16Length = source.Length >> 1; // byte => char count
for (int i = 0; i < utf16Length; i++)
{
var ch = Unsafe.Add(ref utf16, i);
if ((ushort)ch <= 0x7f) // Fast path for ASCII
{
bytesNeeded++;
}
else if (!char.IsSurrogate(ch))
{
bytesNeeded += EncodingHelper.GetUtf8EncodedBytes((uint)ch);
}
else
{
if (++i >= utf16Length)
{
return(TransformationStatus.NeedMoreSourceData);
}
uint codePoint = (uint)char.ConvertToUtf32(ch, Unsafe.Add(ref utf16, i));
bytesNeeded += EncodingHelper.GetUtf8EncodedBytes(codePoint);
}
}
if ((utf16Length << 1) != source.Length)
{
return(TransformationStatus.NeedMoreSourceData);
}
return(TransformationStatus.Done);
}
