diff options
authornsz <>2012-03-17 13:46:15 +0100
committernsz <>2012-03-17 13:46:15 +0100
commit88cfaf8a142a8c57beccb89398a6421c4bbf121a (patch)
parentd3fc724759ef08a8032e76e14f8cd96bfb837e17 (diff)
fix i386 fegetround and make fesetround faster
Note that the new fesetround has slightly different semantics: Storing the floating-point environment with fnstenv makes the next fldenv (or fldcw) "non-signaling", so unmasked and pending exceptions does not invoke the exception handler. (These are rare since exceptions are handled immediately and by default all exceptions are masked anyway. But if one manually unmasks an exception in the control word then either sets the corresponding exception flag in the status word or the execution of an exception raising floating-point operation gets interrupted then it may happen). So the old implementation did not trap in some rare cases where the new implementation traps. However POSIX does not specify anything like the x87 exception handling traps and the fnstenv/fldenv pair is significantly slower than the fnstcw/fldcw pair (new code is about 5x faster here and it's dominated by the function call overhead).
1 files changed, 10 insertions, 10 deletions
diff --git a/src/fenv/i386/fenv.s b/src/fenv/i386/fenv.s
index 8148a30d..ee2eae6e 100644
--- a/src/fenv/i386/fenv.s
+++ b/src/fenv/i386/fenv.s
@@ -32,22 +32,22 @@ feraiseexcept:
mov 4(%esp),%ecx
xor %eax,%eax
- sub $32,%esp
- fnstenv (%esp)
+ sub $4,%esp
+ fnstcw (%esp)
andb $0xf3,1(%esp)
- or %ecx,(%esp)
- fldenv (%esp)
- add $32,%esp
+ or %cx,(%esp)
+ fldcw (%esp)
+ add $4,%esp
.global fegetround
.type fegetround,@function
- sub $28,%esp
- fnstenv (%esp)
- mov 4(%esp),%eax
- add $28,%esp
- and $0xc,%ah
+ sub $4,%esp
+ fnstcw (%esp)
+ mov (%esp),%ax
+ add $4,%esp
+ and $0xc00,%eax
.global fegetenv