[PATCH, libfortran]: Committed: Read rounding mode from SSE mxcsr register on x86_64.
Uros Bizjak
ubizjak@gmail.com
Tue Jul 23 09:56:00 GMT 2013
Hello!
On x86_64, we can look into SSE mxcsr register to determine rounding mode.
2013-07-23 Uros Bizjak <ubizjak@gmail.com>
* config/fpu-387.h (get_fpu_rounding_mode): Read rounding mode
from SSE mxcsr register on x86_64.
Tested on x86_64-pc-linux-gnu {,-m32} and committed to mainline svn.
BTW. gfortran.dg/round_4.f90 test will fail on glibc < 2.17 due to
glibc bug 3479 [1], "Incorrect rounding in strtod()".
[1] http://sourceware.org/bugzilla/show_bug.cgi?id=3479
Uros.
-------------- next part --------------
Index: config/fpu-387.h
===================================================================
--- config/fpu-387.h (revision 201156)
+++ config/fpu-387.h (working copy)
@@ -102,11 +102,11 @@ has_sse (void)
/* i387 rounding modes. */
#define _FPU_RC_NEAREST 0x0
-#define _FPU_RC_DOWN 0x400
-#define _FPU_RC_UP 0x800
-#define _FPU_RC_ZERO 0xc00
+#define _FPU_RC_DOWN 0x1
+#define _FPU_RC_UP 0x2
+#define _FPU_RC_ZERO 0x3
-#define _FPU_RC_MASK 0xc00
+#define _FPU_RC_MASK 0x3
void
@@ -202,8 +202,9 @@ set_fpu_rounding_mode (int round)
__asm__ __volatile__ ("fnstcw\t%0" : "=m" (cw));
- cw &= ~_FPU_RC_MASK;
- cw |= round_mode;
+ /* The x87 round control bits are shifted by 10 bits. */
+ cw &= ~(_FPU_RC_MASK << 10);
+ cw |= round_mode << 10;
__asm__ __volatile__ ("fldcw\t%0" : : "m" (cw));
@@ -213,9 +214,9 @@ set_fpu_rounding_mode (int round)
__asm__ __volatile__ ("%vstmxcsr\t%0" : "=m" (cw_sse));
- /* The SSE round control bits are shifted by 3 bits. */
- cw_sse &= ~(_FPU_RC_MASK << 3);
- cw_sse |= round_mode << 3;
+ /* The SSE round control bits are shifted by 13 bits. */
+ cw_sse &= ~(_FPU_RC_MASK << 13);
+ cw_sse |= round_mode << 13;
__asm__ __volatile__ ("%vldmxcsr\t%0" : : "m" (cw_sse));
}
@@ -224,13 +225,27 @@ set_fpu_rounding_mode (int round)
int
get_fpu_rounding_mode (void)
{
+ int round_mode;
+
+#ifdef __x86_64__
+ unsigned int cw;
+
+ __asm__ __volatile__ ("%vstmxcsr\t%0" : "=m" (cw));
+
+ /* The SSE round control bits are shifted by 13 bits. */
+ round_mode = cw >> 13;
+#else
unsigned short cw;
__asm__ __volatile__ ("fnstcw\t%0" : "=m" (cw));
- cw &= _FPU_RC_MASK;
+ /* The x87 round control bits are shifted by 10 bits. */
+ round_mode = cw >> 10;
+#endif
- switch (cw)
+ round_mode &= _FPU_RC_MASK;
+
+ switch (round_mode)
{
case _FPU_RC_NEAREST:
return GFC_FPE_TONEAREST;
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