commit 90be6c5fc541fb83699b949e26e6eb9044a2d096
author Jingwei Zhang <jingwei.zhang@intel.com> Fri Sep 19 00:50:00 2014 +0800
committer Mingwei Shi <mingwei.shi@intel.com> Fri Sep 19 00:50:00 2014 +0800
tree fe4d9d01f395bc4525ee5fd23d77ff5944978794
parent 0bd28a43dae87c808f6af61ad3dba042b35be7e7

The nextafter functions use the wrong next representable value

From C99 standard: “The nextafter functions determine the next representable value, in the type of the function,
after x in the direction of y, where x and y are first converted to the type of the function”.
The next representable value of 0.0 in direction of -1.0 is -4.9406564584124654e-324, not 0.0.

Similar thing holds for nextafterf, nextafterl, nexttowardf, nexttoward, and nexttowardl.
The tests pass either way, since the error is within the tolerance, but how it is written is wrong.

Change-Id: I1338eeffe3de8031a48f46e1b07146bc07dc2f0a
Signed-off-by: Jingwei Zhang <jingwei.zhang@intel.com>
Signed-off-by: Mingwei Shi <mingwei.shi@intel.com>

tests/math_test.cpp

diff --git a/tests/math_test.cpp b/tests/math_test.cpp
index 2203db9..b4604f8 100644
--- a/tests/math_test.cpp
+++ b/tests/math_test.cpp
@@ -1032,13 +1032,13 @@
 TEST(math, nextafter) {
   ASSERT_DOUBLE_EQ(0.0, nextafter(0.0, 0.0));
   ASSERT_DOUBLE_EQ(4.9406564584124654e-324, nextafter(0.0, 1.0));
-  ASSERT_DOUBLE_EQ(0.0, nextafter(0.0, -1.0));
+  ASSERT_DOUBLE_EQ(-4.9406564584124654e-324, nextafter(0.0, -1.0));
 }
 
 TEST(math, nextafterf) {
   ASSERT_FLOAT_EQ(0.0f, nextafterf(0.0f, 0.0f));
   ASSERT_FLOAT_EQ(1.4012985e-45f, nextafterf(0.0f, 1.0f));
-  ASSERT_FLOAT_EQ(0.0f, nextafterf(0.0f, -1.0f));
+  ASSERT_FLOAT_EQ(-1.4012985e-45f, nextafterf(0.0f, -1.0f));
 }
 
 TEST(math, nextafterl) {
@@ -1047,19 +1047,19 @@
   // sizeof(double) == sizeof(long double)
   long double smallest_positive = ldexpl(1.0L, LDBL_MIN_EXP - LDBL_MANT_DIG);
   ASSERT_DOUBLE_EQ(smallest_positive, nextafterl(0.0L, 1.0L));
-  ASSERT_DOUBLE_EQ(0.0L, nextafterl(0.0L, -1.0L));
+  ASSERT_DOUBLE_EQ(-smallest_positive, nextafterl(0.0L, -1.0L));
 }
 
 TEST(math, nexttoward) {
   ASSERT_DOUBLE_EQ(0.0, nexttoward(0.0, 0.0L));
   ASSERT_DOUBLE_EQ(4.9406564584124654e-324, nexttoward(0.0, 1.0L));
-  ASSERT_DOUBLE_EQ(0.0, nexttoward(0.0, -1.0L));
+  ASSERT_DOUBLE_EQ(-4.9406564584124654e-324, nexttoward(0.0, -1.0L));
 }
 
 TEST(math, nexttowardf) {
   ASSERT_FLOAT_EQ(0.0f, nexttowardf(0.0f, 0.0L));
   ASSERT_FLOAT_EQ(1.4012985e-45f, nexttowardf(0.0f, 1.0L));
-  ASSERT_FLOAT_EQ(0.0f, nexttowardf(0.0f, -1.0L));
+  ASSERT_FLOAT_EQ(-1.4012985e-45f, nexttowardf(0.0f, -1.0L));
 }
 
 TEST(math, nexttowardl) {
@@ -1068,7 +1068,7 @@
   // sizeof(double) == sizeof(long double)
   long double smallest_positive = ldexpl(1.0L, LDBL_MIN_EXP - LDBL_MANT_DIG);
   ASSERT_DOUBLE_EQ(smallest_positive, nexttowardl(0.0L, 1.0L));
-  ASSERT_DOUBLE_EQ(0.0L, nexttowardl(0.0L, -1.0L));
+  ASSERT_DOUBLE_EQ(-smallest_positive, nexttowardl(0.0L, -1.0L));
 }
 
 TEST(math, copysign) {
@@ -1095,19 +1095,19 @@
 TEST(math, significand) {
   ASSERT_DOUBLE_EQ(0.0, significand(0.0));
   ASSERT_DOUBLE_EQ(1.2, significand(1.2));
-  ASSERT_DOUBLE_EQ(1.5375, significand(12.3));
+  ASSERT_DOUBLE_EQ(1.53125, significand(12.25));
 }
 
 TEST(math, significandf) {
   ASSERT_FLOAT_EQ(0.0f, significandf(0.0f));
   ASSERT_FLOAT_EQ(1.2f, significandf(1.2f));
-  ASSERT_FLOAT_EQ(1.5375f, significandf(12.3f));
+  ASSERT_FLOAT_EQ(1.53125f, significandf(12.25f));
 }
 
 TEST(math, significandl) {
   ASSERT_DOUBLE_EQ(0.0L, significandl(0.0L));
   ASSERT_DOUBLE_EQ(1.2L, significandl(1.2L));
-  ASSERT_DOUBLE_EQ(1.5375L, significandl(12.3L));
+  ASSERT_DOUBLE_EQ(1.53125L, significandl(12.25L));
 }
 
 TEST(math, scalb) {