From 316e024f63af0d0d2bb0df3dfce2620f4be827d1 Mon Sep 17 00:00:00 2001
From: Rich Felker <dalias@aerifal.cx>
Date: Sat, 17 Mar 2012 19:29:00 -0400
Subject: [PATCH] optimize x86 feclearexcept

if all exception flags will be cleared, we can avoid the expensive
store/reload of the environment and just use the fnclex instruction.
---
 src/fenv/i386/fenv.s | 38 +++++++++++++++++++++-----------------
 1 file changed, 21 insertions(+), 17 deletions(-)

diff --git a/src/fenv/i386/fenv.s b/src/fenv/i386/fenv.s
index 647b7961..e365b8f4 100644
--- a/src/fenv/i386/fenv.s
+++ b/src/fenv/i386/fenv.s
@@ -1,30 +1,34 @@
-2:	not %ecx
-	sub $32,%esp
-	fnstenv (%esp)
-	and %ecx,4(%esp)
-	or %edx,4(%esp)
-	fldenv (%esp)
-	add $32,%esp
-	ret
-
 .global feclearexcept
 .type feclearexcept,@function
 feclearexcept:	
-	xor %eax,%eax
 	mov 4(%esp),%ecx
-	xor %edx,%edx
-	test %ecx,%ecx
-	jnz 2b
+	not %ecx
+	test $0x3f,%ecx
+	jnz 2f
+1:	fnclex
+	xor %eax,%eax
+	ret
+2:	fnstsw %ax
+	and %ecx,%eax
+	jz 1b
+	sub $32,%esp
+	fnstenv (%esp)
+	mov %al,4(%esp)
+	fldenv (%esp)
+	add $32,%esp
+	xor %eax,%eax
 	ret
 
 .global feraiseexcept
 .type feraiseexcept,@function
 feraiseexcept:	
+	mov 4(%esp),%eax
+	sub $32,%esp
+	fnstenv (%esp)
+	or %al,4(%esp)
+	fldenv (%esp)
+	add $32,%esp
 	xor %eax,%eax
-	mov 4(%esp),%edx
-	xor %ecx,%ecx
-	test %edx,%edx
-	jnz 2b
 	ret
 
 .global fesetround