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Be more precise about which conversions of NaNs

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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
This commit is contained in:
Dale Johannesen
2008-10-06 22:59:10 +00:00
parent e93f5db6e5
commit 2df5eec2ff
3 changed files with 49 additions and 3 deletions
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21
lib/Support/APFloat.cpp
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@ -1721,17 +1721,32 @@ APFloat::convert(const fltSemantics &toSemantics,
} 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;