floor: Implement result sign according to IEEE 754.

* lib/floor.c (FUNC): Return +0.0 for 0 < x < 1.
* tests/test-floor2.c (floor_reference): Keep in sync with lib/floor.c.
* tests/test-floorf2.c (floorf_reference): Likewise.
* tests/test-floorf-ieee.c (main): Test also values between -1 and 1.
* tests/test-floor-ieee.c (main): Likewise.
* tests/test-floorl-ieee.c (main): Likewise.

7 files changed, 59 insertions, 4 deletions

diff --git a/ChangeLog b/ChangeLog
index 298bae1b5c..de2decf06f 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,5 +1,15 @@
 2010-12-22  Bruno Haible  <bruno@clisp.org>
 
+	floor: Implement result sign according to IEEE 754.
+	* lib/floor.c (FUNC): Return +0.0 for 0 < x < 1.
+	* tests/test-floor2.c (floor_reference): Keep in sync with lib/floor.c.
+	* tests/test-floorf2.c (floorf_reference): Likewise.
+	* tests/test-floorf-ieee.c (main): Test also values between -1 and 1.
+	* tests/test-floor-ieee.c (main): Likewise.
+	* tests/test-floorl-ieee.c (main): Likewise.
+
+2010-12-22  Bruno Haible  <bruno@clisp.org>
+
 	getaddrinfo: Update doc.
 	* doc/posix-functions/gai_strerror.texi: Return type is also different
 	on AIX and HP-UX.
diff --git a/lib/floor.c b/lib/floor.c
index 593b526826..73a7e1eb08 100644
--- a/lib/floor.c
+++ b/lib/floor.c
@@ -1,5 +1,5 @@
 /* Round towards negative infinity.
-   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
@@ -65,8 +65,12 @@ FUNC (DOUBLE x)
 
   if (z > L_(0.0))
     {
+      /* For 0 < x < 1, return +0.0 even if the current rounding mode is
+         FE_DOWNWARD.  */
+      if (z < L_(1.0))
+        z = L_(0.0);
       /* Avoid rounding errors for values near 2^k, where k >= MANT_DIG-1.  */
-      if (z < TWO_MANT_DIG)
+      else if (z < TWO_MANT_DIG)
         {
           /* Round to the next integer (nearest or up or down, doesn't matter).  */
           z += TWO_MANT_DIG;
diff --git a/tests/test-floor-ieee.c b/tests/test-floor-ieee.c
index 0051d67f25..4446e8b148 100644
--- a/tests/test-floor-ieee.c
+++ b/tests/test-floor-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 (floor (0.0)));
   ASSERT (!!signbit (floor (minus_zerod)) == !!signbit (minus_zerod));
+  /* Positive numbers.  */
+  ASSERT (!signbit (floor (0.3)));
+  ASSERT (!signbit (floor (0.7)));
+  /* Negative numbers.  */
+  ASSERT (!!signbit (floor (-0.3)) == !!signbit (minus_zerod));
+  ASSERT (!!signbit (floor (-0.7)) == !!signbit (minus_zerod));
 
   return 0;
 }
diff --git a/tests/test-floor2.c b/tests/test-floor2.c
index 1aca8ab5f3..e2391993bd 100644
--- a/tests/test-floor2.c
+++ b/tests/test-floor2.c
@@ -63,8 +63,12 @@ floor_reference (DOUBLE x)
 
   if (z > L_(0.0))
     {
+      /* For 0 < x < 1, return +0.0 even if the current rounding mode is
+         FE_DOWNWARD.  */
+      if (z < L_(1.0))
+        z = L_(0.0);
       /* Avoid rounding errors for values near 2^k, where k >= MANT_DIG-1.  */
-      if (z < TWO_MANT_DIG)
+      else if (z < TWO_MANT_DIG)
         {
           /* Round to the next integer (nearest or up or down, doesn't matter).  */
           z += TWO_MANT_DIG;
diff --git a/tests/test-floorf-ieee.c b/tests/test-floorf-ieee.c
index da13848738..c4925d2b17 100644
--- a/tests/test-floorf-ieee.c
+++ b/tests/test-floorf-ieee.c
@@ -37,9 +37,20 @@ main (int argc, char **argv _GL_UNUSED)
 {
   float (*my_floorf) (float) = argc ? floorf : dummy;
 
+  /* 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 (my_floorf (0.0f)));
   ASSERT (!!signbit (my_floorf (minus_zerof)) == !!signbit (minus_zerof));
+  /* Positive numbers.  */
+  ASSERT (!signbit (my_floorf (0.3f)));
+  ASSERT (!signbit (my_floorf (0.7f)));
+  /* Negative numbers.  */
+  ASSERT (!!signbit (my_floorf (-0.3f)) == !!signbit (minus_zerof));
+  ASSERT (!!signbit (my_floorf (-0.7f)) == !!signbit (minus_zerof));
 
   return 0;
 }
diff --git a/tests/test-floorf2.c b/tests/test-floorf2.c
index 6811728cc3..b7f18a84fb 100644
--- a/tests/test-floorf2.c
+++ b/tests/test-floorf2.c
@@ -63,8 +63,12 @@ floorf_reference (DOUBLE x)
 
   if (z > L_(0.0))
     {
+      /* For 0 < x < 1, return +0.0 even if the current rounding mode is
+         FE_DOWNWARD.  */
+      if (z < L_(1.0))
+        z = L_(0.0);
       /* Avoid rounding errors for values near 2^k, where k >= MANT_DIG-1.  */
-      if (z < TWO_MANT_DIG)
+      else if (z < TWO_MANT_DIG)
         {
           /* Round to the next integer (nearest or up or down, doesn't matter).  */
           z += TWO_MANT_DIG;
diff --git a/tests/test-floorl-ieee.c b/tests/test-floorl-ieee.c
index 05e836e516..ec4b4e18cb 100644
--- a/tests/test-floorl-ieee.c
+++ b/tests/test-floorl-ieee.c
@@ -29,9 +29,20 @@ 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 (floorl (0.0L)));
   ASSERT (!!signbit (floorl (minus_zerol)) == !!signbit (minus_zerol));
+  /* Positive numbers.  */
+  ASSERT (!signbit (floorl (0.3L)));
+  ASSERT (!signbit (floorl (0.7L)));
+  /* Negative numbers.  */
+  ASSERT (!!signbit (floorl (-0.3L)) == !!signbit (minus_zerol));
+  ASSERT (!!signbit (floorl (-0.7L)) == !!signbit (minus_zerol));
 
   return 0;
 }