From 88cfaf8a142a8c57beccb89398a6421c4bbf121a Mon Sep 17 00:00:00 2001 From: nsz Date: Sat, 17 Mar 2012 13:46:15 +0100 Subject: 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). --- src/fenv/i386/fenv.s | 20 ++++++++++---------- 1 file changed, 10 insertions(+), 10 deletions(-) (limited to 'src/fenv') 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: fesetround: 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 ret .global fegetround .type fegetround,@function fegetround: - 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 ret .global fegetenv -- cgit v1.2.1