Be more precise about which conversions of NaNs
are Inexact. (These are not Inexact as defined
by IEEE754, but that seems like a reasonable way
to abstract what happens: information is lost.)
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@57218 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Support/APFloat.cpp b/lib/Support/APFloat.cpp
index 3e37d79..b93f1d1 100644
--- a/lib/Support/APFloat.cpp
+++ b/lib/Support/APFloat.cpp
@@ -1721,17 +1721,32 @@
} else if (category == fcNaN) {
int shift = toSemantics.precision - semantics->precision;
// Do this now so significandParts gets the right answer
+ const fltSemantics *oldSemantics = semantics;
semantics = &toSemantics;
+ fs = opOK;
// No normalization here, just truncate
if (shift>0)
APInt::tcShiftLeft(significandParts(), newPartCount, shift);
- else if (shift < 0)
- APInt::tcShiftRight(significandParts(), newPartCount, -shift);
+ else if (shift < 0) {
+ unsigned ushift = -shift;
+ // We mark this as Inexact if we are losing information. This happens
+ // if are shifting out something other than 0s, or if the x87 long
+ // double input did not have its integer bit set (pseudo-NaN), or if the
+ // x87 long double input did not have its QNan bit set (because the x87
+ // hardware sets this bit when converting a lower-precision NaN to
+ // x87 long double).
+ if (APInt::tcLSB(significandParts(), newPartCount) < ushift)
+ fs = opInexact;
+ if (oldSemantics == &APFloat::x87DoubleExtended &&
+ (!(*significandParts() & 0x8000000000000000ULL) ||
+ !(*significandParts() & 0x4000000000000000ULL)))
+ fs = opInexact;
+ APInt::tcShiftRight(significandParts(), newPartCount, ushift);
+ }
// gcc forces the Quiet bit on, which means (float)(double)(float_sNan)
// does not give you back the same bits. This is dubious, and we
// don't currently do it. You're really supposed to get
// an invalid operation signal at runtime, but nobody does that.
- fs = opOK;
} else {
semantics = &toSemantics;
fs = opOK;