[PATCH v2 4/4] alpha: fix trunc for big input values

[Aurelien Jarno]

The alpha specific version of trunc and truncf always add and subtract
0x1.0p23 or 0x1.0p52 even for big values. This causes this kind of
errors in the testsuite:

  Failure: Test: trunc_towardzero (0x1p107)
  Result:
   is:          1.6225927682921334e+32   0x1.fffffffffffffp+106
   should be:   1.6225927682921336e+32   0x1.0000000000000p+107
   difference:  1.8014398509481984e+16   0x1.0000000000000p+54
   ulp       :  0.5000
   max.ulp   :  0.0000

Change this by returning the input value when its absolute value is
greater than 0x1.0p23 or 0x1.0p52. NaN have to go through the add and
subtract operations to get possibly silenced.

Finally remove the code to handle inexact exception, trunc should never
generate such an exception.

Changelog:
	* sysdeps/alpha/fpu/s_trunc.c (__trunc): Return the input value
	when its absolute value is greater than 0x1.0p52.
	[_IEEE_FP_INEXACT] Remove.
	* sysdeps/alpha/fpu/s_truncf.c (__truncf): Return the input value
	when its absolute value is greater than 0x1.0p23.
	[_IEEE_FP_INEXACT] Remove.
---
 ChangeLog                    | 6 ++++++
 sysdeps/alpha/fpu/s_trunc.c  | 7 +++----
 sysdeps/alpha/fpu/s_truncf.c | 7 +++----
 3 files changed, 12 insertions(+), 8 deletions(-)

v1 -> v2:
 - use isgreaterequal instead of checking for nan and doing a comparison

diff --git a/ChangeLog b/ChangeLog
index c7dbf18..2168d31 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -11,6 +11,12 @@
 	* sysdeps/alpha/fpu/s_rint.c (__rint): Add argument with itself
 	when it is a NaN.
 	* sysdeps/alpha/fpu/s_rintf.c (__rintf): Likewise.
+	* sysdeps/alpha/fpu/s_trunc.c (__trunc): Return the input value
+	when its absolute value is greater than 0x1.0p52.
+	[_IEEE_FP_INEXACT] Remove.
+	* sysdeps/alpha/fpu/s_truncf.c (__truncf): Return the input value
+	when its absolute value is greater than 0x1.0p23.
+	[_IEEE_FP_INEXACT] Remove.
 
 2016-07-08  Adhemerval Zanella  <adhemerval.zanella@linaro.org>
 
diff --git a/sysdeps/alpha/fpu/s_trunc.c b/sysdeps/alpha/fpu/s_trunc.c
index 16cb114..4b986a6 100644
--- a/sysdeps/alpha/fpu/s_trunc.c
+++ b/sysdeps/alpha/fpu/s_trunc.c
@@ -28,12 +28,11 @@ __trunc (double x)
   double two52 = copysign (0x1.0p52, x);
   double r, tmp;
 
+  if (isgreaterequal (fabs (x), 0x1.0p52))
+    return x;
+
   __asm (
-#ifdef _IEEE_FP_INEXACT
-	 "addt/suic %2, %3, %1\n\tsubt/suic %1, %3, %0"
-#else
 	 "addt/suc %2, %3, %1\n\tsubt/suc %1, %3, %0"
-#endif
 	 : "=&f"(r), "=&f"(tmp)
 	 : "f"(x), "f"(two52));
 
diff --git a/sysdeps/alpha/fpu/s_truncf.c b/sysdeps/alpha/fpu/s_truncf.c
index 2290f28..3e93356 100644
--- a/sysdeps/alpha/fpu/s_truncf.c
+++ b/sysdeps/alpha/fpu/s_truncf.c
@@ -27,12 +27,11 @@ __truncf (float x)
   float two23 = copysignf (0x1.0p23, x);
   float r, tmp;
 
+  if (isgreaterequal (fabsf (x), 0x1.0p23))
+    return x;
+
   __asm (
-#ifdef _IEEE_FP_INEXACT
-	 "adds/suic %2, %3, %1\n\tsubs/suic %1, %3, %0"
-#else
 	 "adds/suc %2, %3, %1\n\tsubs/suc %1, %3, %0"
-#endif
 	 : "=&f"(r), "=&f"(tmp)
 	 : "f"(x), "f"(two23));
 
-- 
2.8.1