[Bug target/25960] __gcc_add doesn't handle -0.0L properly
-- amodra at bigpond dot net dot au changed: What|Removed |Added AssignedTo|unassigned at gcc dot gnu |amodra at bigpond dot net |dot org |dot au Status|REOPENED|ASSIGNED Last reconfirmed|2006-01-25 14:39:25 |2006-02-02 23:32:19 date|| http://gcc.gnu.org/bugzilla/show_bug.cgi?id=25960
[Bug target/25960] __gcc_add doesn't handle -0.0L properly
--- Comment #6 from geoffk at gcc dot gnu dot org 2006-02-02 08:50 --- I agree with Alan. Although the format is not compatible with IEEE arithmetic, this applies only because the arithmetic is different, not the handling of special cases. In every case where the inputs are exactly representable as a double (including +/-0, Inf, and NaN) and 'double' arithmetic would be exact, the result of the computation in this 'long double' representation should be the same as if it had been done in 'double'. As for the patch, it looks right to me, but it's probably better for performance if instead it does if (zz == 0.0) return z; -- geoffk at gcc dot gnu dot org changed: What|Removed |Added Status|RESOLVED|REOPENED Resolution|INVALID | http://gcc.gnu.org/bugzilla/show_bug.cgi?id=25960
[Bug target/25960] __gcc_add doesn't handle -0.0L properly
--- Comment #4 from amodra at bigpond dot net dot au 2006-02-02 04:30 --- I don't think this bug should have been closed so quickly. Fixing __gcc_qadd to properly handle a -0 result is trivial, and only costs one extra compare and branch. The multiply and divide support in darwin-ldouble.c already have special code for -0, with a comment Preserve -0, so I think lack of such a test in __gcc_qadd is simply an oversight. -- amodra at bigpond dot net dot au changed: What|Removed |Added CC||munroesj at us dot ibm dot ||com http://gcc.gnu.org/bugzilla/show_bug.cgi?id=25960
[Bug target/25960] __gcc_add doesn't handle -0.0L properly
--- Comment #5 from amodra at bigpond dot net dot au 2006-02-02 06:18
---
* config/rs6000/darwin-ldouble.c (__gcc_qadd): Preserve -0.0 result.
Index: gcc/config/rs6000/darwin-ldouble.c
===
--- gcc/config/rs6000/darwin-ldouble.c (revision 110484)
+++ gcc/config/rs6000/darwin-ldouble.c (working copy)
@@ -117,10 +117,15 @@ __gcc_qadd (double a, double aa, double
{
q = a - z;
zz = q + c + (a - (q + z)) + aa + cc;
- xh = z + zz;
-
- if (nonfinite (xh))
- return xh;
+ xh = z;
+ /* Keep -0 result. */
+ if (zz != 0.0)
+ {
+ xh += zz;
+
+ if (nonfinite (xh))
+ return xh;
+ }
x.dval[0] = xh;
x.dval[1] = z - xh + zz;
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=25960
[Bug target/25960] __gcc_add doesn't handle -0.0L properly
--- Comment #2 from dje at gcc dot gnu dot org 2006-01-27 17:59 --- The IBM 128-bit extended floating point format is not fully compliant with IEEE 754. It is functioning as designed. -- http://gcc.gnu.org/bugzilla/show_bug.cgi?id=25960
[Bug target/25960] __gcc_add doesn't handle -0.0L properly
--- Comment #3 from pinskia at gcc dot gnu dot org 2006-01-27 18:02 --- So closing as invalid. -- pinskia at gcc dot gnu dot org changed: What|Removed |Added Status|NEW |RESOLVED Resolution||INVALID http://gcc.gnu.org/bugzilla/show_bug.cgi?id=25960
[Bug target/25960] __gcc_add doesn't handle -0.0L properly
--- Comment #1 from pinskia at gcc dot gnu dot org 2006-01-25 14:39 --- Confirmed on powerpc-darwin also which uses IBM's 128bit long double format by default. -- pinskia at gcc dot gnu dot org changed: What|Removed |Added CC||geoffk at gcc dot gnu dot ||org Status|UNCONFIRMED |NEW Ever Confirmed|0 |1 GCC target triplet|powerpc*-linux |powerpc*-* Keywords||wrong-code Last reconfirmed|-00-00 00:00:00 |2006-01-25 14:39:25 date|| http://gcc.gnu.org/bugzilla/show_bug.cgi?id=25960
