/// <summary>
/// A copy of the logic in Rune.DecodeFromUtf16.
/// </summary>
public static OperationStatus DecodeScalarValueFromUtf16(ReadOnlySpan <char> source, out uint result, out int charsConsumed)
{
const char ReplacementChar = '\uFFFD';
if (!source.IsEmpty)
{
// First, check for the common case of a BMP scalar value.
// If this is correct, return immediately.
uint firstChar = source[0];
if (!UnicodeUtility.IsSurrogateCodePoint(firstChar))
{
result = firstChar;
charsConsumed = 1;
return(OperationStatus.Done);
}
// First thing we saw was a UTF-16 surrogate code point.
// Let's optimistically assume for now it's a high surrogate and hope
// that combining it with the next char yields useful results.
if (1 < (uint)source.Length)
{
uint secondChar = source[1];
if (UnicodeUtility.IsHighSurrogateCodePoint(firstChar) && UnicodeUtility.IsLowSurrogateCodePoint(secondChar))
{
// Success! Formed a supplementary scalar value.
result = UnicodeUtility.GetScalarFromUtf16SurrogatePair(firstChar, secondChar);
charsConsumed = 2;
return(OperationStatus.Done);
}
else
{
// Either the first character was a low surrogate, or the second
// character was not a low surrogate. This is an error.
goto InvalidData;
}
}
else if (!UnicodeUtility.IsHighSurrogateCodePoint(firstChar))
{
// Quick check to make sure we're not going to report NeedMoreData for
// a single-element buffer where the data is a standalone low surrogate
// character. Since no additional data will ever make this valid, we'll
// report an error immediately.
goto InvalidData;
}
}
// If we got to this point, the input buffer was empty, or the buffer
// was a single element in length and that element was a high surrogate char.
charsConsumed = source.Length;
result = ReplacementChar;
return(OperationStatus.NeedMoreData);
InvalidData:
charsConsumed = 1; // maximal invalid subsequence for UTF-16 is always a single code unit in length
result = ReplacementChar;
return(OperationStatus.InvalidData);
}