APFloat is derived from C code using fixed width storage for the matntissa. When converting to C++ I changed it to variable- width storage for space efficiency and generality reasons. Unfortunately this leads to a complication during float->float conversions that I missed that isn't present when using fixed width storage. Dale - I think this solves the issue correctly whilst preserving correct rounding. Does it fix the problem case you had? Neil. -------------- next part -------------- Index: lib/Support/APFloat.cpp ==================================================================--- lib/Support/APFloat.cpp (revision 42219) +++ lib/Support/APFloat.cpp (working copy) @@ -1318,39 +1318,44 @@ APFloat::convert(const fltSemantics &toSemantics, roundingMode rounding_mode) { - unsigned int newPartCount; + lostFraction lostFraction; + unsigned int newPartCount, oldPartCount; opStatus fs; - + + lostFraction = lfExactlyZero; newPartCount = partCountForBits(toSemantics.precision + 1); + oldPartCount = partCount(); - /* If our new form is wider, re-allocate our bit pattern into wider - storage. - If we're narrowing from multiple words to 1 words, copy to the single - word. If we are losing information by doing this, we would have to - worry about rounding; right now the only case is f80 -> shorter - conversion, and we are keeping all 64 significant bits, so it's OK. */ - if(newPartCount > partCount()) { + /* Handle storage complications. If our new form is wider, + re-allocate our bit pattern into wider storage. If it is + narrower, we ignore the excess parts, but if narrowing to a + single part we need to free the old storage. */ + if (newPartCount > oldPartCount) { integerPart *newParts; newParts = new integerPart[newPartCount]; APInt::tcSet(newParts, 0, newPartCount); - APInt::tcAssign(newParts, significandParts(), partCount()); + APInt::tcAssign(newParts, significandParts(), oldPartCount); freeSignificand(); significand.parts = newParts; - } else if (newPartCount==1 && newPartCount < partCount()) { - integerPart newPart; - - APInt::tcSet(&newPart, 0, newPartCount); - APInt::tcAssign(&newPart, significandParts(), partCount()); - freeSignificand(); - significand.part = newPart; + } else if (newPartCount < oldPartCount) { + /* Capture any lost fraction through truncation of parts so we get + correct rounding whilst normalizing. */ + lostFraction = lostFractionThroughTruncation + (significandParts(), oldPartCount, newPartCount * integerPartWidth); + if (newPartCount == 1) + { + integerPart newPart = significandParts()[0]; + freeSignificand(); + significand.part = newPart; + } } if(category == fcNormal) { /* Re-interpret our bit-pattern. */ exponent += toSemantics.precision - semantics->precision; semantics = &toSemantics; - fs = normalize(rounding_mode, lfExactlyZero); + fs = normalize(rounding_mode, lostFraction); } else { semantics = &toSemantics; fs = opOK;