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[13/13] AArch64: Cleanup fenv implementation

Message ID 001701cfeee7$e1d0fe60$a572fb20$@com
State New
Headers show

Commit Message

Wilco Oct. 23, 2014, 5:36 p.m. UTC 
Improve feenableexcept performance - avoid an unnecessary FPCR read in case
the FPCR does not change. Also improve the logic of the return value.

ChangeLog:
2014-10-23  Wilco Dijkstra  <wdijkstr@arm.com>

	* sysdeps/aarch64/fpu/feenablxcpt.c (feenableexcept):
	Optimize to avoid an unnecessary FPCR read.

---
 sysdeps/aarch64/fpu/feenablxcpt.c | 16 +++++++---------
 1 file changed, 7 insertions(+), 9 deletions(-)

Comments

Marcus Shawcroft Dec. 18, 2014, 4:29 p.m. UTC | #1 
On 23 October 2014 at 18:36, Wilco Dijkstra <wdijkstr@arm.com> wrote:
> Improve feenableexcept performance - avoid an unnecessary FPCR read in case
> the FPCR does not change. Also improve the logic of the return value.
>
> ChangeLog:
> 2014-10-23  Wilco Dijkstra  <wdijkstr@arm.com>
>
>         * sysdeps/aarch64/fpu/feenablxcpt.c (feenableexcept):
>         Optimize to avoid an unnecessary FPCR read.

OK /M
diff mbox

Patch

diff --git a/sysdeps/aarch64/fpu/feenablxcpt.c b/sysdeps/aarch64/fpu/feenablxcpt.c
index 763248f..dfb4120 100644
--- a/sysdeps/aarch64/fpu/feenablxcpt.c
+++ b/sysdeps/aarch64/fpu/feenablxcpt.c
@@ -24,24 +24,22 @@  feenableexcept (int excepts)
 {
   fpu_control_t fpcr;
   fpu_control_t fpcr_new;
+  fpu_control_t updated_fpcr;
 
   _FPU_GETCW (fpcr);
   excepts &= FE_ALL_EXCEPT;
   fpcr_new = fpcr | (excepts << FE_EXCEPT_SHIFT);
 
   if (fpcr != fpcr_new)
-    _FPU_SETCW (fpcr_new);
-
-  /* Trapping exceptions are optional in AArch64 the relevant enable
-     bits in FPCR are RES0 hence the absence of support can be
-     detected by reading back the FPCR and comparing with the required
-     value.  */
-  if (excepts)
     {
-      fpu_control_t updated_fpcr;
+      _FPU_SETCW (fpcr_new);
 
+      /* Trapping exceptions are optional in AArch64; the relevant enable
+	 bits in FPCR are RES0 hence the absence of support can be detected
+	 by reading back the FPCR and comparing with the required value.  */
       _FPU_GETCW (updated_fpcr);
-      if (((updated_fpcr >> FE_EXCEPT_SHIFT) & excepts) != excepts)
+
+      if (fpcr_new & ~updated_fpcr)
 	return -1;
     }