private static bool TryFormatFloatingPoint <T>(T value, Span <byte> destination, out int bytesWritten, StandardFormat format) where T : IFormattable, ISpanFormattable
{
Span <char> formatText = stackalloc char[0];
if (!format.IsDefault)
{
formatText = stackalloc char[StandardFormat.FormatStringLength];
int formatTextLength = format.Format(formatText);
formatText = formatText.Slice(0, formatTextLength);
}
// We first try to format into a stack-allocated buffer, and if it succeeds, we can avoid
// all allocation. If that fails, we fall back to allocating strings. If it proves impactful,
// that allocation (as well as roundtripping from byte to char and back to byte) could be avoided by
// calling into a refactored Number.FormatSingle/Double directly.
const int StackBufferLength = 128; // large enough to handle the majority cases
Span <char> stackBuffer = stackalloc char[StackBufferLength];
ReadOnlySpan <char> utf16Text = stackalloc char[0];
// Try to format into the stack buffer. If we're successful, we can avoid all allocations.
if (value.TryFormat(stackBuffer, out int formattedLength, formatText, CultureInfo.InvariantCulture))
{
utf16Text = stackBuffer.Slice(0, formattedLength);
}
private static bool TryFormatFloatingPoint <T>(T value, Span <byte> destination, out int bytesWritten, StandardFormat format) where T : IFormattable, ISpanFormattable
{
if (format.IsDefault)
{
format = 'G';
}
switch (format.Symbol)
{
case 'g':
case 'G':
if (format.Precision != StandardFormat.NoPrecision)
{
throw new NotSupportedException(SR.Argument_GWithPrecisionNotSupported);
}
break;
case 'f':
case 'F':
case 'e':
case 'E':
break;
default:
return(FormattingHelpers.TryFormatThrowFormatException(out bytesWritten));
}
Span <char> formatText = stackalloc char[StandardFormat.FormatStringLength];
int formattedLength = format.Format(formatText);
formatText = formatText.Slice(0, formattedLength);
// We first try to format into a stack-allocated buffer, and if it succeeds, we can avoid
// all allocation. If that fails, we fall back to allocating strings. If it proves impactful,
// that allocation (as well as roundtripping from byte to char and back to byte) could be avoided by
// calling into a refactored Number.FormatSingle/Double directly.
const int StackBufferLength = 128; // large enough to handle the majority cases
Span <char> stackBuffer = stackalloc char[StackBufferLength];
ReadOnlySpan <char> utf16Text = stackalloc char[0];
// Try to format into the stack buffer. If we're successful, we can avoid all allocations.
if (value.TryFormat(stackBuffer, out formattedLength, formatText, CultureInfo.InvariantCulture))
{
utf16Text = stackBuffer.Slice(0, formattedLength);
}
else
{
// The stack buffer wasn't large enough. If the destination buffer isn't at least as
// big as the stack buffer, we know the whole operation will eventually fail, so we
// can just fail now.
if (destination.Length <= StackBufferLength)
{
bytesWritten = 0;
return(false);
}
// Fall back to using a string format and allocating a string for the resulting formatted value.
utf16Text = value.ToString(new string(formatText), CultureInfo.InvariantCulture);
}
// Copy the value to the destination, if it's large enough.
if (utf16Text.Length > destination.Length)
{
bytesWritten = 0;
return(false);
}
for (int i = 0; i < utf16Text.Length; i++)
{
Debug.Assert(utf16Text[i] < 128, "A culture-invariant ToString() of a floating point expected to produce ASCII characters only.");
destination[i] = (byte)utf16Text[i];
}
bytesWritten = utf16Text.Length;
return(true);
}