// TODO: this whole routine is too slow. It does div and mod twice, which are both costly (especially that some JITs cannot optimize it).
// It does it twice to avoid reversing the formatted buffer, which can be tricky given it should handle arbitrary cultures.
// One optimization I thought we could do is to do div/mod once and store digits in a temp buffer (but that would allocate). Modification to the idea would be to store the digits in a local struct
// Another idea possibly worth tying would be to special case cultures that have constant digit size, and go back to the format + reverse buffer approach.
private static bool TryFormatDecimal(ulong value, Span <byte> buffer, Format.Parsed format, EncodingData formattingData, out int bytesWritten)
{
if (format.IsDefault)
{
format.Symbol = 'G';
}
format.Symbol = Char.ToUpperInvariant(format.Symbol); // TODO: this is costly. I think the transformation should happen in Parse
Precondition.Require(format.Symbol == 'D' || format.Symbol == 'G' || format.Symbol == 'N');
// Reverse value on decimal basis, count digits and trailing zeros before the decimal separator
ulong reversedValueExceptFirst = 0;
var digitsCount = 1;
var trailingZerosCount = 0;
// We reverse the digits in numeric form because reversing encoded digits is hard and/or costly.
// If value contains 20 digits, its reversed value will not fit into ulong size.
// So reverse it till last digit (reversedValueExceptFirst will have all the digits except the first one).
while (value >= 10)
{
var digit = value % 10UL;
value = value / 10UL;
if (reversedValueExceptFirst == 0 && digit == 0)
{
trailingZerosCount++;
}
else
{
reversedValueExceptFirst = reversedValueExceptFirst * 10UL + digit;
digitsCount++;
}
}
bytesWritten = 0;
int digitBytes;
// If format is D and precision is greater than digitsCount + trailingZerosCount, append leading zeros
if (format.Symbol == 'D' && format.HasPrecision)
{
var leadingZerosCount = format.Precision - digitsCount - trailingZerosCount;
while (leadingZerosCount-- > 0)
{
if (!formattingData.TryWriteDigitOrSymbol(0, buffer.Slice(bytesWritten), out digitBytes))
{
bytesWritten = 0;
return(false);
}
bytesWritten += digitBytes;
}
}
// Append first digit
if (!formattingData.TryWriteDigit(value, buffer.Slice(bytesWritten), out digitBytes))
{
bytesWritten = 0;
return(false);
}
bytesWritten += digitBytes;
digitsCount--;
if (format.Symbol == 'N')
{
const int GroupSize = 3;
// Count amount of digits before first group separator. It will be reset to groupSize every time digitsLeftInGroup == zero
var digitsLeftInGroup = (digitsCount + trailingZerosCount) % GroupSize;
if (digitsLeftInGroup == 0)
{
if (digitsCount + trailingZerosCount > 0)
{
// There is a new group immediately after the first digit
if (!formattingData.TryWriteSymbol(EncodingData.Symbol.GroupSeparator, buffer.Slice(bytesWritten), out digitBytes))
{
bytesWritten = 0;
return(false);
}
bytesWritten += digitBytes;
}
digitsLeftInGroup = GroupSize;
}
// Append digits
while (reversedValueExceptFirst > 0)
{
if (digitsLeftInGroup == 0)
{
if (!formattingData.TryWriteSymbol(EncodingData.Symbol.GroupSeparator, buffer.Slice(bytesWritten), out digitBytes))
{
bytesWritten = 0;
return(false);
}
bytesWritten += digitBytes;
digitsLeftInGroup = GroupSize;
}
var nextDigit = reversedValueExceptFirst % 10UL;
reversedValueExceptFirst = reversedValueExceptFirst / 10UL;
if (!formattingData.TryWriteDigit(nextDigit, buffer.Slice(bytesWritten), out digitBytes))
{
bytesWritten = 0;
return(false);
}
bytesWritten += digitBytes;
digitsLeftInGroup--;
}
// Append trailing zeros if any
while (trailingZerosCount-- > 0)
{
if (digitsLeftInGroup == 0)
{
if (!formattingData.TryWriteSymbol(EncodingData.Symbol.GroupSeparator, buffer.Slice(bytesWritten), out digitBytes))
{
bytesWritten = 0;
return(false);
}
bytesWritten += digitBytes;
digitsLeftInGroup = GroupSize;
}
if (!formattingData.TryWriteDigitOrSymbol(0, buffer.Slice(bytesWritten), out digitBytes))
{
bytesWritten = 0;
return(false);
}
bytesWritten += digitBytes;
digitsLeftInGroup--;
}
}
else
{
while (reversedValueExceptFirst > 0)
{
var bufferSlice = buffer.Slice(bytesWritten);
var nextDigit = reversedValueExceptFirst % 10UL;
reversedValueExceptFirst = reversedValueExceptFirst / 10UL;
if (!formattingData.TryWriteDigit(nextDigit, bufferSlice, out digitBytes))
{
bytesWritten = 0;
return(false);
}
bytesWritten += digitBytes;
}
// Append trailing zeros if any
while (trailingZerosCount-- > 0)
{
if (!formattingData.TryWriteDigitOrSymbol(0, buffer.Slice(bytesWritten), out digitBytes))
{
bytesWritten = 0;
return(false);
}
bytesWritten += digitBytes;
}
}
// If format is N and precision is not defined or is greater than zero, append trailing zeros after decimal point
if (format.Symbol == 'N')
{
int trailingZerosAfterDecimalCount = format.HasPrecision ? format.Precision : 2;
if (trailingZerosAfterDecimalCount > 0)
{
if (!formattingData.TryWriteSymbol(EncodingData.Symbol.DecimalSeparator, buffer.Slice(bytesWritten), out digitBytes))
{
bytesWritten = 0;
return(false);
}
bytesWritten += digitBytes;
while (trailingZerosAfterDecimalCount-- > 0)
{
if (!formattingData.TryWriteDigitOrSymbol(0, buffer.Slice(bytesWritten), out digitBytes))
{
bytesWritten = 0;
return(false);
}
bytesWritten += digitBytes;
}
}
}
return(true);
}
// TODO: this whole routine is too slow. It does div and mod twice, which are both costly (especially that some JITs cannot optimize it).
// It does it twice to avoid reversing the formatted buffer, which can be tricky given it should handle arbitrary cultures.
// One optimization I thought we could do is to do div/mod once and store digits in a temp buffer (but that would allocate). Modification to the idea would be to store the digits in a local struct
// Another idea possibly worth tying would be to special case cultures that have constant digit size, and go back to the format + reverse buffer approach.
private static bool TryFormatDecimal(ulong value, Span<byte> buffer, Format.Parsed format, EncodingData formattingData, out int bytesWritten)
{
if(format.IsDefault)
{
format.Symbol = 'G';
}
format.Symbol = Char.ToUpperInvariant(format.Symbol); // TODO: this is costly. I think the transformation should happen in Parse
Precondition.Require(format.Symbol == 'D' || format.Symbol == 'G' || format.Symbol == 'N');
// Reverse value on decimal basis, count digits and trailing zeros before the decimal separator
ulong reversedValueExceptFirst = 0;
var digitsCount = 1;
var trailingZerosCount = 0;
// We reverse the digits in numeric form because reversing encoded digits is hard and/or costly.
// If value contains 20 digits, its reversed value will not fit into ulong size.
// So reverse it till last digit (reversedValueExceptFirst will have all the digits except the first one).
while (value >= 10)
{
var digit = value % 10UL;
value = value / 10UL;
if (reversedValueExceptFirst == 0 && digit == 0)
{
trailingZerosCount++;
}
else
{
reversedValueExceptFirst = reversedValueExceptFirst * 10UL + digit;
digitsCount++;
}
}
bytesWritten = 0;
int digitBytes;
// If format is D and precision is greater than digitsCount + trailingZerosCount, append leading zeros
if (format.Symbol == 'D' && format.HasPrecision)
{
var leadingZerosCount = format.Precision - digitsCount - trailingZerosCount;
while (leadingZerosCount-- > 0)
{
if (!formattingData.TryWriteDigitOrSymbol(0, buffer.Slice(bytesWritten), out digitBytes))
{
bytesWritten = 0;
return false;
}
bytesWritten += digitBytes;
}
}
// Append first digit
if (!formattingData.TryWriteDigit(value, buffer.Slice(bytesWritten), out digitBytes))
{
bytesWritten = 0;
return false;
}
bytesWritten += digitBytes;
digitsCount--;
if (format.Symbol == 'N')
{
const int GroupSize = 3;
// Count amount of digits before first group separator. It will be reset to groupSize every time digitsLeftInGroup == zero
var digitsLeftInGroup = (digitsCount + trailingZerosCount) % GroupSize;
if (digitsLeftInGroup == 0)
{
if (digitsCount + trailingZerosCount > 0)
{
// There is a new group immediately after the first digit
if (!formattingData.TryWriteSymbol(EncodingData.Symbol.GroupSeparator, buffer.Slice(bytesWritten), out digitBytes))
{
bytesWritten = 0;
return false;
}
bytesWritten += digitBytes;
}
digitsLeftInGroup = GroupSize;
}
// Append digits
while (reversedValueExceptFirst > 0)
{
if (digitsLeftInGroup == 0)
{
if (!formattingData.TryWriteSymbol(EncodingData.Symbol.GroupSeparator, buffer.Slice(bytesWritten), out digitBytes))
{
bytesWritten = 0;
return false;
}
bytesWritten += digitBytes;
digitsLeftInGroup = GroupSize;
}
var nextDigit = reversedValueExceptFirst % 10UL;
reversedValueExceptFirst = reversedValueExceptFirst / 10UL;
if (!formattingData.TryWriteDigit(nextDigit, buffer.Slice(bytesWritten), out digitBytes))
{
bytesWritten = 0;
return false;
}
bytesWritten += digitBytes;
digitsLeftInGroup--;
}
// Append trailing zeros if any
while (trailingZerosCount-- > 0)
{
if (digitsLeftInGroup == 0)
{
if (!formattingData.TryWriteSymbol(EncodingData.Symbol.GroupSeparator, buffer.Slice(bytesWritten), out digitBytes))
{
bytesWritten = 0;
return false;
}
bytesWritten += digitBytes;
digitsLeftInGroup = GroupSize;
}
if (!formattingData.TryWriteDigitOrSymbol(0, buffer.Slice(bytesWritten), out digitBytes))
{
bytesWritten = 0;
return false;
}
bytesWritten += digitBytes;
digitsLeftInGroup--;
}
}
else
{
while (reversedValueExceptFirst > 0)
{
var bufferSlice = buffer.Slice(bytesWritten);
var nextDigit = reversedValueExceptFirst % 10UL;
reversedValueExceptFirst = reversedValueExceptFirst / 10UL;
if (!formattingData.TryWriteDigit(nextDigit, bufferSlice, out digitBytes))
{
bytesWritten = 0;
return false;
}
bytesWritten += digitBytes;
}
// Append trailing zeros if any
while (trailingZerosCount-- > 0)
{
if (!formattingData.TryWriteDigitOrSymbol(0, buffer.Slice(bytesWritten), out digitBytes))
{
bytesWritten = 0;
return false;
}
bytesWritten += digitBytes;
}
}
// If format is N and precision is not defined or is greater than zero, append trailing zeros after decimal point
if (format.Symbol == 'N')
{
int trailingZerosAfterDecimalCount = format.HasPrecision ? format.Precision : 2;
if (trailingZerosAfterDecimalCount > 0)
{
if (!formattingData.TryWriteSymbol(EncodingData.Symbol.DecimalSeparator, buffer.Slice(bytesWritten), out digitBytes))
{
bytesWritten = 0;
return false;
}
bytesWritten += digitBytes;
while (trailingZerosAfterDecimalCount-- > 0)
{
if (!formattingData.TryWriteDigitOrSymbol(0, buffer.Slice(bytesWritten), out digitBytes))
{
bytesWritten = 0;
return false;
}
bytesWritten += digitBytes;
}
}
}
return true;
}
