private static unsafe void DoubleToNumber(double value, int precision, ref NumberBuffer number)
{
number.precision = precision;
if (!Double.IsFinite(value))
{
number.scale = Double.IsNaN(value) ? ScaleNAN : ScaleINF;
number.sign = Double.IsNegative(value);
number.digits[0] = '\0';
}
else
{
byte *src = stackalloc byte[_CVTBUFSIZE];
int sign;
fixed(NumberBuffer *pNumber = &number)
{
RuntimeImports._ecvt_s(src, _CVTBUFSIZE, value, precision, &pNumber->scale, &sign);
}
number.sign = sign != 0;
char *dst = number.digits;
if ((char)*src != '0')
{
while (*src != 0)
{
*dst++ = (char)*src++;
}
}
*dst = '\0';
}
}
//
// Convert a Number to a double.
//
internal static bool NumberBufferToDouble(ref NumberBuffer number, out double value)
{
double d = NumberToDouble(ref number);
if (!Double.IsFinite(d))
{
value = default;
return(false);
}
if (d == 0.0)
{
// normalize -0.0 to 0.0
d = 0.0;
}
value = d;
return(true);
}
private static unsafe void DoubleToNumber(double value, int precision, ref NumberBuffer number)
{
Debug.Assert(precision > 0 && precision < 40);
number.precision = precision;
if (!Double.IsFinite(value))
{
number.scale = Double.IsNaN(value) ? ScaleNAN : ScaleINF;
number.sign = Double.IsNegative(value);
number.digits[0] = '\0';
return;
}
byte *tempBuffer = stackalloc byte[MAX_BUFFER_SIZE];
char *dst = number.digits;
number.scale = 0;
number.sign = double.IsNegative(value);
*dst = '\0';
if (value == 0.0)
{
for (int j = 0; j < precision; j++)
{
dst[j] = '0';
}
dst[precision] = '\0';
return;
}
//
// Get the number formatted as a string in the form x.xxxxxxexxxx
//
// "%.40e"
byte *format = stackalloc byte[6];
format[0] = (byte)'%';
format[1] = (byte)'.';
format[2] = (byte)'4';
format[3] = (byte)'0';
format[4] = (byte)'e';
format[5] = 0;
int tempBufferLength = Interop.Sys.DoubleToString(value, format, tempBuffer, MAX_BUFFER_SIZE);
Debug.Assert(tempBufferLength > 0 && MAX_BUFFER_SIZE > tempBufferLength);
//
// Calculate the exponent value
//
int exponentIndex = tempBufferLength - 1;
while (tempBuffer[exponentIndex] != (byte)'e' && exponentIndex > 0)
{
exponentIndex--;
}
Debug.Assert(exponentIndex > 0 && (exponentIndex < tempBufferLength - 1));
int i = exponentIndex + 1;
int exponentSign = 1;
if (tempBuffer[i] == '-')
{
exponentSign = -1;
i++;
}
else if (tempBuffer[i] == '+')
{
i++;
}
int exponentValue = 0;
while (i < tempBufferLength)
{
Debug.Assert(tempBuffer[i] >= (byte)'0' && tempBuffer[i] <= (byte)'9');
exponentValue = exponentValue * 10 + (tempBuffer[i] - (byte)'0');
i++;
}
exponentValue *= exponentSign;
//
// Determine decimal location.
//
if (exponentValue == 0)
{
number.scale = 1;
}
else
{
number.scale = exponentValue + 1;
}
//
// Copy the string from the temp buffer upto precision characters, removing the sign, and decimal as required.
//
i = 0;
int mantissaIndex = 0;
while (i < precision && mantissaIndex < exponentIndex)
{
if (tempBuffer[mantissaIndex] >= (byte)'0' && tempBuffer[mantissaIndex] <= (byte)'9')
{
dst[i] = (char)tempBuffer[mantissaIndex];
i++;
}
mantissaIndex++;
}
while (i < precision)
{
dst[i] = '0'; // append zeros as needed
i++;
}
dst[i] = '\0';
//
// Round if needed
//
if (mantissaIndex >= exponentIndex || tempBuffer[mantissaIndex] < (byte)'5')
{
return; // rounding is not needed
}
i = precision - 1;
while (dst[i] == '9' && i > 0)
{
dst[i] = '0';
i--;
}
if (i == 0 && dst[i] == '9')
{
dst[i] = '1';
number.scale++;
}
else
{
dst[i]++;
}
}
