Function AdjustToPrecision

ext/src/llvm/APFloat.cpp:3612–3640

Removes data from the given significand until it is no more precise than is required for the desired precision.

  /// Removes data from the given significand until it is no more
  /// precise than is required for the desired precision.
  void AdjustToPrecision(APInt &significand,
                         int &exp, unsigned FormatPrecision) {
    unsigned bits = significand.getActiveBits();

    // 196/59 is a very slight overestimate of lg_2(10).
    unsigned bitsRequired = (FormatPrecision * 196 + 58) / 59;

    if (bits <= bitsRequired) return;

    unsigned tensRemovable = (bits - bitsRequired) * 59 / 196;
    if (!tensRemovable) return;

    exp += tensRemovable;

    APInt divisor(significand.getBitWidth(), 1);
    APInt powten(significand.getBitWidth(), 10);
    while (true) {
      if (tensRemovable & 1)
        divisor *= powten;
      tensRemovable >>= 1;
      if (!tensRemovable) break;
      powten *= powten;
    }

    significand = significand.udiv(divisor);

    // Truncate the significand down to its active bit count.
    significand = significand.trunc(significand.getActiveBits());
  }


  void AdjustToPrecision(SmallVectorImpl<char> &buffer,