trunc: Implement result sign according to IEEE 754.

* lib/trunc.c (MIN, MINUS_ZERO): New macros.
(FUNC): Return +0.0 for 0 < x < 1 and -0.0 for -1 < x < 0.
* tests/test-trunc2.c: Include minus-zero.h.
(MINUS_ZERO): New macro.
(trunc_reference): Keep in sync with lib/trunc.c.
* tests/test-truncf2.c: Include minus-zero.h.
(MINUS_ZERO): New macro.
(truncf_reference): Keep in sync with lib/trunc.c.
* tests/test-truncf-ieee.c (main): Test also values between -1 and 1.
* tests/test-trunc-ieee.c (main): Likewise.
* tests/test-truncl-ieee.c (main): Likewise.

1 files changed, 11 insertions, 0 deletions

diff --git a/tests/test-truncf-ieee.c b/tests/test-truncf-ieee.c
index c5c779ae70..76d06079e8 100644
--- a/tests/test-truncf-ieee.c
+++ b/tests/test-truncf-ieee.c
@@ -24,9 +24,20 @@
 int
 main ()
 {
+  /* See IEEE 754, section 6.3:
+       "the sign of the result of the round floating-point number to
+        integral value operation is the sign of the operand. These rules
+        shall apply even when operands or results are zero or infinite."  */
+
   /* Zero.  */
   ASSERT (!signbit (truncf (0.0f)));
   ASSERT (!!signbit (truncf (minus_zerof)) == !!signbit (minus_zerof));
+  /* Positive numbers.  */
+  ASSERT (!signbit (truncf (0.3f)));
+  ASSERT (!signbit (truncf (0.7f)));
+  /* Negative numbers.  */
+  ASSERT (!!signbit (truncf (-0.3f)) == !!signbit (minus_zerof));
+  ASSERT (!!signbit (truncf (-0.7f)) == !!signbit (minus_zerof));
 
   return 0;
 }