Method convertFromDecimalString

ext/src/llvm/APFloat.cpp:2672–2791

}

Expected<IEEEFloat::opStatus>
IEEEFloat::convertFromDecimalString(StringRef str, roundingMode rounding_mode) {
  decimalInfo D;
  opStatus fs;

  /* Scan the text.  */
  StringRef::iterator p = str.begin();
  if (Error Err = interpretDecimal(p, str.end(), &D))
    return std::move(Err);

  /* Handle the quick cases.  First the case of no significant digits,
     i.e. zero, and then exponents that are obviously too large or too
     small.  Writing L for log 10 / log 2, a number d.ddddd*10^exp
     definitely overflows if

           (exp - 1) * L >= maxExponent

     and definitely underflows to zero where

           (exp + 1) * L <= minExponent - precision

     With integer arithmetic the tightest bounds for L are

           93/28 < L < 196/59            [ numerator <= 256 ]
           42039/12655 < L < 28738/8651  [ numerator <= 65536 ]
  */

  // Test if we have a zero number allowing for strings with no null terminators
  // and zero decimals with non-zero exponents.
  //
  // We computed firstSigDigit by ignoring all zeros and dots. Thus if
  // D->firstSigDigit equals str.end(), every digit must be a zero and there can
  // be at most one dot. On the other hand, if we have a zero with a non-zero
  // exponent, then we know that D.firstSigDigit will be non-numeric.
  if (D.firstSigDigit == str.end() || decDigitValue(*D.firstSigDigit) >= 10U) {
    category = fcZero;
    fs = opOK;

  /* Check whether the normalized exponent is high enough to overflow
     max during the log-rebasing in the max-exponent check below. */
  } else if (D.normalizedExponent - 1 > INT_MAX / 42039) {
    fs = handleOverflow(rounding_mode);

  /* If it wasn't, then it also wasn't high enough to overflow max
     during the log-rebasing in the min-exponent check.  Check that it
     won't overflow min in either check, then perform the min-exponent
     check. */
  } else if (D.normalizedExponent - 1 < INT_MIN / 42039 ||
             (D.normalizedExponent + 1) * 28738 <=
               8651 * (semantics->minExponent - (int) semantics->precision)) {
    /* Underflow to zero and round.  */
    category = fcNormal;
    zeroSignificand();
    fs = normalize(rounding_mode, lfLessThanHalf);

  /* We can finally safely perform the max-exponent check. */
  } else if ((D.normalizedExponent - 1) * 42039
             >= 12655 * semantics->maxExponent) {