public static bool Run(double value, int precision, ref NumberBuffer number)
{
// ========================================================================================================================================
// This implementation is based on the paper: http://www.cs.tufts.edu/~nr/cs257/archive/florian-loitsch/printf.pdf
// You must read this paper to fully understand the code.
//
// Deviation: Instead of generating shortest digits, we generate the digits according to the input count.
// Therefore, we do not need m+ and m- which are used to determine the exact range of values.
// ========================================================================================================================================
//
// Overview:
//
// The idea of Grisu3 is to leverage additional bits and cached power of ten to produce the digits.
// We need to create a handmade floating point data structure DiyFp to extend the bits of double.
// We also need to cache the powers of ten for digits generation. By choosing the correct index of powers
// we need to start with, we can eliminate the expensive big num divide operation.
//
// Grisu3 is imprecision for some numbers. Fortunately, the algorithm itself can determine that and give us
// a success/fail flag. We may fall back to other algorithms (For instance, Dragon4) if it fails.
//
// w: the normalized DiyFp from the input value.
// mk: The index of the cached powers.
// cmk: The cached power.
// D: Product: w * cmk.
// kappa: A factor used for generating digits. See step 5 of the Grisu3 procedure in the paper.
// Handle sign bit.
if (double.IsNegative(value))
{
value = -value;
number.IsNegative = true;
}
else
{
number.IsNegative = false;
}
// Step 1: Determine the normalized DiyFp w.
DiyFp.GenerateNormalizedDiyFp(value, out DiyFp w);
// Step 2: Find the cached power of ten.
// Compute the proper index mk.
int mk = KComp(w.e + DiyFp.SignificandLength);
// Retrieve the cached power of ten.
CachedPower(mk, out DiyFp cmk, out int decimalExponent);
// Step 3: Scale the w with the cached power of ten.
DiyFp.Multiply(ref w, ref cmk, out DiyFp D);
// Step 4: Generate digits.
bool isSuccess = DigitGen(ref D, precision, number.GetDigitsPointer(), out int length, out int kappa);
if (isSuccess)
{
number.Digits[precision] = (byte)('\0');
number.Scale = (length - decimalExponent + kappa);
}
return(isSuccess);
}
