private static bool TrySkipIntegerDigits(string text, ref int pos, NumberStyles styles, NumberFormatInfo format)
{
if (pos == text.Length)
{
return(false);
}
var start = pos;
if (format?.NumberDecimalSeparator != null &&
Skipper.TrySkip(text, ref pos, format.NumberDecimalSeparator))
{
if (!IntReader.IsDigit(text, pos))
{
pos = start;
return(false);
}
pos = start;
return(true);
}
if (!IntReader.IsDigit(text[pos]))
{
return(false);
}
while (pos < text.Length)
{
var i = text[pos] - '0';
if (i >= 0 && i <= 9)
{
pos++;
continue;
}
if ((styles & NumberStyles.AllowThousands) != 0)
{
if (format?.NumberDecimalSeparator != null &&
Skipper.TrySkip(text, ref pos, format.NumberGroupSeparator))
{
continue;
}
}
break;
}
return(pos - start < 310);
}
private static bool TrySkipExponent(string text, ref int pos)
{
if (Skipper.TrySkip(text, ref pos, 'E'))
{
return(true);
}
if (Skipper.TrySkip(text, ref pos, "e"))
{
return(true);
}
return(false);
}
private static bool TryReadSign(string text, ref int pos, NumberFormatInfo format, out Sign sign)
{
if (Skipper.TrySkip(text, ref pos, format.PositiveSign))
{
sign = Sign.Positive;
return(true);
}
if (Skipper.TrySkip(text, ref pos, format.NegativeSign))
{
sign = Sign.Negative;
return(true);
}
sign = Sign.None;
return(false);
}
internal static bool TryRead(
string text,
ref int pos,
NumberStyles style,
IFormatProvider provider,
out double result)
{
result = 0;
var start = pos;
if (string.IsNullOrEmpty(text))
{
return(false);
}
if (!IsValidFloatingPointStyle(style))
{
return(false);
}
if ((style & NumberStyles.AllowHexSpecifier) != 0)
{
return(false);
}
if ((style & NumberStyles.AllowLeadingWhite) != 0)
{
_ = WhiteSpaceReader.TryRead(text, ref pos);
}
if (char.IsWhiteSpace(text[pos]))
{
return(false);
}
if (TrySkipDoubleDigits(text, ref pos, style, provider))
{
return(TryParseSubString(text, start, ref pos, style, provider, out result));
}
if (provider is null)
{
provider = CultureInfo.CurrentCulture;
}
var format = NumberFormatInfo.GetInstance(provider);
if (Skipper.TrySkip(text, ref pos, format.NaNSymbol))
{
result = double.NaN;
return(true);
}
if (Skipper.TrySkip(text, ref pos, format.PositiveInfinitySymbol))
{
result = double.PositiveInfinity;
return(true);
}
if (Skipper.TrySkip(text, ref pos, format.NegativeInfinitySymbol))
{
result = double.NegativeInfinity;
return(true);
}
pos = start;
return(false);
}
// Try parse a double from digits ignoring +-Inf and NaN
private static bool TrySkipDoubleDigits(
string text,
ref int pos,
NumberStyles style,
IFormatProvider provider)
{
var start = pos;
var format = NumberFormatInfo.GetInstance(provider);
if (TryReadSign(text, ref pos, format, out _))
{
if ((style & NumberStyles.AllowLeadingSign) == 0)
{
pos = start;
return(false);
}
}
if (!TrySkipIntegerDigits(text, ref pos, style, format))
{
pos = start;
return(false);
}
if (Skipper.TrySkip(text, ref pos, format.NumberDecimalSeparator))
{
if ((style & NumberStyles.AllowDecimalPoint) == 0)
{
pos = start;
return(false);
}
_ = TrySkipFractionDigits(text, ref pos);
}
if (TrySkipExponent(text, ref pos))
{
if ((style & NumberStyles.AllowExponent) == 0)
{
pos = start;
return(false);
}
_ = TryReadSign(text, ref pos, format, out var exponentSign);
if (TrySkipExponentDigits(text, ref pos))
{
return(true);
}
// This is a tricky spot we read digits followed by (sign) exponent
// then no digits were thrown. I choose to return the double here.
// Both alternatives will be wrong in some situations.
// returning false here would make it impossible to parse 1.2eV
var backStep = exponentSign == Sign.None
? 1
: 2;
pos -= backStep;
return(true);
}
return(true);
}
