private static void CreateExponentialRepresentation(
Span <char> decimal_digits,
int length,
int exponent,
StackStringBuilder writer)
{
Debug.Assert(length != 0);
writer.Append(decimal_digits[0]);
if (length != 1)
{
writer.Append('.');
writer.Append(decimal_digits, 1, length - 1);
}
writer.Append(exponent_character_);
if (exponent < 0)
{
writer.Append('-');
exponent = -exponent;
}
else if (exponent == 0)
{
writer.Append('0');
return;
}
else
{
writer.Append('+');
}
Debug.Assert(exponent < 1e4);
if (exponent >= 100)
{
writer.Append((char)('0' + exponent / 100));
exponent %= 100;
writer.Append((char)('0' + exponent / 10));
exponent %= 10;
writer.Append((char)('0' + exponent));
}
else if (exponent >= 10)
{
writer.Append((char)('0' + exponent / 10));
exponent %= 10;
writer.Append((char)('0' + exponent));
}
else
{
writer.Append((char)('0' + exponent));
}
}
private static void CreateDecimalRepresentation(
Span <char> decimal_digits,
int length,
int decimal_point,
int digits_after_point,
StackStringBuilder writer)
{
// Create a representation that is padded with zeros if needed.
if (decimal_point <= 0)
{
// "0.00000decimal_rep".
writer.Append('0');
if (digits_after_point > 0)
{
writer.Append('.');
writer.Append('0', -decimal_point);
Debug.Assert(length <= digits_after_point - (-decimal_point));
writer.Append(decimal_digits, length);
int remaining_digits = digits_after_point - (-decimal_point) - length;
writer.Append('0', remaining_digits);
}
}
else if (decimal_point >= length)
{
// "decimal_rep0000.00000" or "decimal_rep.0000"
writer.Append(decimal_digits, length);
writer.Append('0', decimal_point - length);
if (digits_after_point > 0)
{
writer.Append('.');
writer.Append('0', digits_after_point);
}
}
else
{
// "decima.l_rep000"
Debug.Assert(digits_after_point > 0);
writer.Append(decimal_digits, decimal_point);
writer.Append('.');
Debug.Assert(length - decimal_point <= digits_after_point);
writer.Append(decimal_digits, decimal_point,
length - decimal_point);
int remaining_digits = digits_after_point - (length - decimal_point);
writer.Append('0', remaining_digits);
}
}
internal unsafe static string TryFormat(double value)
{
Span <char> resultBuf = stackalloc char[24];
var ssb = new StackStringBuilder(resultBuf);
if (value < 0.0)
{
ssb.Append('-');
value = -value;
}
GrisuDouble grisuDouble = new GrisuDouble(value);
if (grisuDouble.IsSpecial)
{
return(null);
}
Span <char> decimal_rep = stackalloc char[18];
int decimal_point;
int decimal_rep_length;
if (!DoubleToShortestAscii(ref grisuDouble, decimal_rep, out decimal_rep_length, out decimal_point))
{
return(null);
}
int decimalRepLength = decimal_rep_length;
if (decimal_point < 1)
{
decimalRepLength += -decimal_point + 1;
}
else if (decimal_point >= decimal_rep_length)
{
decimalRepLength += decimal_point - decimal_rep_length + 1;
}
int exponent = decimal_point - 1;
int absExponent = Math.Abs(exponent);
int exponentRepLength = decimal_rep_length + 3;
if (exponent < 0)
{
++exponentRepLength;
}
if (absExponent >= 10)
{
++exponentRepLength;
if (absExponent >= 100)
{
++exponentRepLength;
}
}
if (decimalRepLength <= exponentRepLength)
{
CreateDecimalRepresentation(decimal_rep, decimal_rep_length,
decimal_point,
Math.Max(0, decimal_rep_length - decimal_point),
ssb);
}
else
{
CreateExponentialRepresentation(decimal_rep, decimal_rep_length, exponent,
ssb);
}
return(ssb.ToString());
}