From: Bruno Haible <bruno@clisp.org>
Date: Wed, 22 Dec 2010 15:10:58 +0000 (+0100)
Subject: round: Implement result sign according to IEEE 754.
X-Git-Tag: v0.1~3493
X-Git-Url: http://erislabs.org.uk/gitweb/?a=commitdiff_plain;h=2adbc9c81f9a8b3681f44c3103d2ab617506f6f2;p=gnulib.git

round: Implement result sign according to IEEE 754.

* lib/round.c (MIN, MINUS_ZERO): New macros.
(FUNC): Return -0.0 for -0.5 < x < 0.
* tests/test-roundf-ieee.c (main): Test also values between -1 and 1.
* tests/test-round-ieee.c (main): Likewise.
* tests/test-roundl-ieee.c (main): Likewise.
---

diff --git a/ChangeLog b/ChangeLog
index b8af66437..be3b0fa4c 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,5 +1,12 @@
 2010-12-22  Bruno Haible  <bruno@clisp.org>
 
+	round: Implement result sign according to IEEE 754.
+	* lib/round.c (MIN, MINUS_ZERO): New macros.
+	(FUNC): Return -0.0 for -0.5 < x < 0.
+	* tests/test-roundf-ieee.c (main): Test also values between -1 and 1.
+	* tests/test-round-ieee.c (main): Likewise.
+	* tests/test-roundl-ieee.c (main): Likewise.
+
 	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.
diff --git a/lib/round.c b/lib/round.c
index c935ddc10..07ec4cdf8 100644
--- a/lib/round.c
+++ b/lib/round.c
@@ -1,5 +1,5 @@
 /* Round toward nearest, breaking ties away from zero.
-   Copyright (C) 2007, 2009, 2010 Free Software Foundation, Inc.
+   Copyright (C) 2007, 2010 Free Software Foundation, Inc.
 
    This program is free software; you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published by
@@ -29,6 +29,7 @@
 # define CEIL ceill
 # define DOUBLE long double
 # define MANT_DIG LDBL_MANT_DIG
+# define MIN LDBL_MIN
 # define L_(literal) literal##L
 # define HAVE_FLOOR_AND_CEIL HAVE_FLOORL_AND_CEILL
 #elif ! defined USE_FLOAT
@@ -37,6 +38,7 @@
 # define CEIL ceil
 # define DOUBLE double
 # define MANT_DIG DBL_MANT_DIG
+# define MIN DBL_MIN
 # define L_(literal) literal
 # define HAVE_FLOOR_AND_CEIL 1
 #else /* defined USE_FLOAT */
@@ -45,10 +47,18 @@
 # define CEIL ceilf
 # define DOUBLE float
 # define MANT_DIG FLT_MANT_DIG
+# define MIN FLT_MIN
 # define L_(literal) literal##f
 # define HAVE_FLOOR_AND_CEIL HAVE_FLOORF_AND_CEILF
 #endif
 
+/* -0.0.  See minus-zero.h.  */
+#if defined __hpux || defined __sgi || defined __ICC
+# define MINUS_ZERO (-MIN * MIN)
+#else
+# define MINUS_ZERO L_(-0.0)
+#endif
+
 /* If we're being included from test-round2[f].c, it already defined names for
    our round implementations.  Otherwise, pick the preferred implementation for
    this machine. */
@@ -133,7 +143,7 @@ FLOOR_FREE_ROUND (DOUBLE x)
     {
       /* Avoid rounding error for x = -(0.5 - 2^(-MANT_DIG-1)).  */
       if (z > - L_(0.5))
-        z = L_(0.0);
+        z = MINUS_ZERO;
       /* Avoid rounding errors for values near -2^k, where k >= MANT_DIG-1.  */
       else if (z > -TWO_MANT_DIG)
         {
diff --git a/tests/test-round-ieee.c b/tests/test-round-ieee.c
index 0d5ad86df..817acd12a 100644
--- a/tests/test-round-ieee.c
+++ b/tests/test-round-ieee.c
@@ -25,9 +25,20 @@
 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 (round (0.0)));
   ASSERT (!!signbit (round (minus_zerod)) == !!signbit (minus_zerod));
+  /* Positive numbers.  */
+  ASSERT (!signbit (round (0.3)));
+  ASSERT (!signbit (round (0.7)));
+  /* Negative numbers.  */
+  ASSERT (!!signbit (round (-0.3)) == !!signbit (minus_zerod));
+  ASSERT (!!signbit (round (-0.7)) == !!signbit (minus_zerod));
 
   return 0;
 }
diff --git a/tests/test-roundf-ieee.c b/tests/test-roundf-ieee.c
index 3948401a2..e7d9001cb 100644
--- a/tests/test-roundf-ieee.c
+++ b/tests/test-roundf-ieee.c
@@ -25,9 +25,20 @@
 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 (roundf (0.0f)));
   ASSERT (!!signbit (roundf (minus_zerof)) == !!signbit (minus_zerof));
+  /* Positive numbers.  */
+  ASSERT (!signbit (roundf (0.3f)));
+  ASSERT (!signbit (roundf (0.7f)));
+  /* Negative numbers.  */
+  ASSERT (!!signbit (roundf (-0.3f)) == !!signbit (minus_zerof));
+  ASSERT (!!signbit (roundf (-0.7f)) == !!signbit (minus_zerof));
 
   return 0;
 }
diff --git a/tests/test-roundl-ieee.c b/tests/test-roundl-ieee.c
index ca4ac9ed7..431005bae 100644
--- a/tests/test-roundl-ieee.c
+++ b/tests/test-roundl-ieee.c
@@ -30,9 +30,20 @@ main ()
 
   BEGIN_LONG_DOUBLE_ROUNDING ();
 
+  /* 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 (roundl (0.0L)));
   ASSERT (!!signbit (roundl (minus_zerol)) == !!signbit (minus_zerol));
+  /* Positive numbers.  */
+  ASSERT (!signbit (roundl (0.3L)));
+  ASSERT (!signbit (roundl (0.7L)));
+  /* Negative numbers.  */
+  ASSERT (!!signbit (roundl (-0.3L)) == !!signbit (minus_zerol));
+  ASSERT (!!signbit (roundl (-0.7L)) == !!signbit (minus_zerol));
 
   return 0;
 }