Add fuzzy floating point comparison macro

Add a test macro that allows comparing two floating point values for
equality within a certain tolerance.

This macro has been independently reimplemented by various projects:

 * Clutter
 * Graphene
 * colord

https://gitlab.gnome.org/GNOME/glib/issues/914

docs/reference/glib/glib-sections.txt

@@ -3147,6 +3147,7 @@ g_assert_cmpint
 g_assert_cmpuint
 g_assert_cmphex
 g_assert_cmpfloat
+g_assert_cmpfloat_with_epsilon
 g_assert_cmpmem
 g_assert_no_error
 g_assert_error

glib/gtestutils.c

@@ -89,10 +89,11 @@
  *
  * In addition to the traditional g_assert(), the test framework provides
  * an extended set of assertions for comparisons: g_assert_cmpfloat(),
- * g_assert_cmpint(), g_assert_cmpuint(), g_assert_cmphex(),
- * g_assert_cmpstr(), and g_assert_cmpmem(). The advantage of these
- * variants over plain g_assert() is that the assertion messages can be
- * more elaborate, and include the values of the compared entities.
+ * g_assert_cmpfloat_with_epsilon(), g_assert_cmpint(), g_assert_cmpuint(),
+ * g_assert_cmphex(), g_assert_cmpstr(), and g_assert_cmpmem(). The
+ * advantage of these variants over plain g_assert() is that the assertion
+ * messages can be more elaborate, and include the values of the compared
+ * entities.
  *
  * A full example of creating a test suite with two tests using fixtures:
  * |[<!-- language="C" -->
@@ -636,6 +637,23 @@
  * Since: 2.16
  */
 
+/**
+ * g_assert_cmpfloat_with_epsilon:
+ * @n1: an floating point number
+ * @n2: another floating point number
+ * @epsilon: a numeric value that expresses the expected tolerance
+ *   between @n1 and @n2
+ *
+ * Debugging macro to compare two floating point numbers within an epsilon.
+ *
+ * The effect of `g_assert_cmpfloat_with_epsilon (n1, n2, epsilon)` is
+ * the same as `g_assert_true (abs (n1 - n2) < epsilon)`. The advantage
+ * of this macro is that it can produce a message that includes the
+ * actual values of @n1 and @n2.
+ *
+ * Since: 2.58
+ */
+
 /**
  * g_assert_cmpmem:
  * @m1: pointer to a buffer

glib/gtestutils.h

@@ -69,6 +69,13 @@ typedef void (*GTestFixtureFunc) (gpointer      fixture,
                                                g_assertion_message_cmpnum (G_LOG_DOMAIN, __FILE__, __LINE__, G_STRFUNC, \
                                                  #n1 " " #cmp " " #n2, (long double) __n1, #cmp, (long double) __n2, 'f'); \
                                         } G_STMT_END
+#define g_assert_cmpfloat_with_epsilon(n1,n2,epsilon) \
+                                        G_STMT_START { \
+                                             double __n1 = (n1), __n2 = (n2), __epsilon = (epsilon); \
+                                             if (G_APPROX_VALUE (__n1,  __n2, __epsilon)) ; else \
+                                               g_assertion_message_cmpnum (G_LOG_DOMAIN, __FILE__, __LINE__, G_STRFUNC, \
+                                                 #n1 " == " #n2 " (+/- " #epsilon ")", __n1, "==", __n2, 'f'); \
+                                        } G_STMT_END
 #define g_assert_cmpmem(m1, l1, m2, l2) G_STMT_START {\
                                              gconstpointer __m1 = m1, __m2 = m2; \
                                              int __l1 = l1, __l2 = l2; \

glib/tests/testing.c

@@ -60,6 +60,13 @@ test_assertions_bad_cmpmem_data (void)
   exit (0);
 }
 
+static void
+test_assertions_bad_cmpfloat_epsilon (void)
+{
+  g_assert_cmpfloat_with_epsilon (3.14, 3.15, 0.001);
+  exit (0);
+}
+
 static void
 test_assertions (void)
 {
@@ -68,6 +75,8 @@ test_assertions (void)
   g_assert_cmphex (2, ==, 2);
   g_assert_cmpfloat (3.3, !=, 7);
   g_assert_cmpfloat (7, <=, 3 + 4);
+  g_assert_cmpfloat_with_epsilon (3.14, 3.15, 0.01);
+  g_assert_cmpfloat_with_epsilon (3.14159, 3.1416, 0.0001);
   g_assert (TRUE);
   g_assert_cmpstr ("foo", !=, "faa");
   fuu = g_strdup_printf ("f%s", "uu");
@@ -98,6 +107,10 @@ test_assertions (void)
   g_test_trap_assert_failed ();
   g_test_trap_assert_stderr ("*assertion failed*");
   g_test_trap_assert_stderr_unmatched ("*assertion failed*len*");
+
+  g_test_trap_subprocess ("/misc/assertions/subprocess/bad_cmpfloat_epsilon", 0, 0);
+  g_test_trap_assert_failed ();
+  g_test_trap_assert_stderr ("*assertion failed*");
 }
 
 /* test g_test_timer* API */
@@ -740,6 +753,7 @@ main (int   argc,
   g_test_add_func ("/misc/assertions/subprocess/bad_cmpint", test_assertions_bad_cmpint);
   g_test_add_func ("/misc/assertions/subprocess/bad_cmpmem_len", test_assertions_bad_cmpmem_len);
   g_test_add_func ("/misc/assertions/subprocess/bad_cmpmem_data", test_assertions_bad_cmpmem_data);
+  g_test_add_func ("/misc/assertions/subprocess/bad_cmpfloat_epsilon", test_assertions_bad_cmpfloat_epsilon);
   g_test_add_data_func ("/misc/test-data", (void*) 0xc0c0baba, test_data_test);
   g_test_add ("/misc/primetoul", Fixturetest, (void*) 0xc0cac01a, fixturetest_setup, fixturetest_test, fixturetest_teardown);
   if (g_test_perf())