math.c: C99-like atan2

* math.c (math_atan2): return values like as expected by C99 if
  both two arguments are infinity.  based on the patch by cremno
  phobia <cremno AT mail.ru> in [ruby-core:62310].  [Feature #9799]

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@45805 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

1 files changed, 18 insertions, 1 deletions

diff --git a/math.c b/math.c
index 70cd26cb07..b042e7dbea 100644
--- a/math.c
+++ b/math.c
@@ -55,6 +55,10 @@ VALUE rb_eMathDomainError;
  *    Math.atan2(1.0, 0.0)   #=> 1.5707963267948966
  *    Math.atan2(1.0, -1.0)  #=> 2.356194490192345
  *    Math.atan2(0.0, -1.0)  #=> 3.141592653589793
+ *    Math.atan2(INFINITY, INFINITY)   #=> 0.7853981633974483
+ *    Math.atan2(INFINITY, -INFINITY)  #=> 2.356194490192345
+ *    Math.atan2(-INFINITY, INFINITY)  #=> -0.7853981633974483
+ *    Math.atan2(-INFINITY, -INFINITY) #=> -2.356194490192345
  *
  */
 
@@ -75,7 +79,20 @@ math_atan2(VALUE obj, VALUE y, VALUE x)
 	    return DBL2NUM(M_PI);
 	return DBL2NUM(-M_PI);
     }
-    if (isinf(dx) && isinf(dy)) domain_error("atan2");
+#if !(defined(HAVE_ATAN2L) && defined(HAVE_ATAN2F)) || 1
+    /* assume atan2() doesn't handle Inf as C99 */
+    if (isinf(dx) && isinf(dy)) {
+	/* optimization for FLONUM */
+	if (dx < 0.0) {
+	    const double dz = (3.0 * M_PI / 4.0);
+	    return (dy < 0.0) ? DBL2NUM(-dz) : DBL2NUM(dz);
+	}
+	else {
+	    const double dz = (M_PI / 4.0);
+	    return (dy < 0.0) ? DBL2NUM(-dz) : DBL2NUM(dz);
+	}
+    }
+#endif
     return DBL2NUM(atan2(dy, dx));
 }