public static bool TryParseSByte(ReadOnlySpan <byte> text, out sbyte value, out int bytesConsumed, StandardFormat format = default, SymbolTable symbolTable = null)
{
symbolTable = symbolTable ?? SymbolTable.InvariantUtf8;
if (!format.IsDefault && format.HasPrecision)
{
throw new NotImplementedException("Format with precision not supported.");
}
if (symbolTable == SymbolTable.InvariantUtf8)
{
if (Parsers.IsHexFormat(format))
{
return(Utf8Parser.TryParse(text, out value, out bytesConsumed, 'X'));
}
else
{
return(Utf8Parser.TryParse(text, out value, out bytesConsumed));
}
}
else if (symbolTable == SymbolTable.InvariantUtf16)
{
ReadOnlySpan <char> utf16Text = MemoryMarshal.Cast <byte, char>(text);
int charactersConsumed;
bool result;
if (Parsers.IsHexFormat(format))
{
result = Utf16Parser.Hex.TryParseSByte(utf16Text, out value, out charactersConsumed);
}
else
{
result = Utf16Parser.TryParseSByte(utf16Text, out value, out charactersConsumed);
}
bytesConsumed = charactersConsumed * sizeof(char);
return(result);
}
if (Parsers.IsHexFormat(format))
{
throw new NotImplementedException("The only supported encodings for hexadecimal parsing are InvariantUtf8 and InvariantUtf16.");
}
if (!(format.IsDefault || format.Symbol == 'G' || format.Symbol == 'g'))
{
throw new NotImplementedException(String.Format("Format '{0}' not supported.", format.Symbol));
}
if (!symbolTable.TryParse(text, out SymbolTable.Symbol nextSymbol, out int thisSymbolConsumed))
{
value = default;
bytesConsumed = 0;
return(false);
}
int sign = 1;
if (nextSymbol == SymbolTable.Symbol.MinusSign)
{
sign = -1;
}
int signConsumed = 0;
if (nextSymbol == SymbolTable.Symbol.PlusSign || nextSymbol == SymbolTable.Symbol.MinusSign)
{
signConsumed = thisSymbolConsumed;
if (!symbolTable.TryParse(text.Slice(signConsumed), out nextSymbol, out thisSymbolConsumed))
{
value = default;
bytesConsumed = 0;
return(false);
}
}
if (nextSymbol > SymbolTable.Symbol.D9)
{
value = default;
bytesConsumed = 0;
return(false);
}
int parsedValue = (int)nextSymbol;
int index = signConsumed + thisSymbolConsumed;
while (index < text.Length)
{
bool success = symbolTable.TryParse(text.Slice(index), out nextSymbol, out thisSymbolConsumed);
if (!success || nextSymbol > SymbolTable.Symbol.D9)
{
bytesConsumed = index;
value = (sbyte)(parsedValue * sign);
return(true);
}
// If parsedValue > (sbyte.MaxValue / 10), any more appended digits will cause overflow.
// if parsedValue == (sbyte.MaxValue / 10), any nextDigit greater than 7 or 8 (depending on sign) implies overflow.
bool positive = sign > 0;
bool nextDigitTooLarge = nextSymbol > SymbolTable.Symbol.D8 || (positive && nextSymbol > SymbolTable.Symbol.D7);
if (parsedValue > sbyte.MaxValue / 10 || (parsedValue == sbyte.MaxValue / 10 && nextDigitTooLarge))
{
bytesConsumed = 0;
value = default;
return(false);
}
index += thisSymbolConsumed;
parsedValue = parsedValue * 10 + (int)nextSymbol;
}
bytesConsumed = text.Length;
value = (sbyte)(parsedValue * sign);
return(true);
}