handle +/-inf.0 and +nan.0 in atan #299

jcubic · Feb 11, 2024 · 5889985 · 5889985
1 parent 4d5c14d
commit 5889985
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Showing 5 changed files with 30 additions and 10 deletions.
diff --git a/dist/std.min.scm b/dist/std.min.scm
diff --git a/dist/std.scm b/dist/std.scm
diff --git a/dist/std.xcb b/dist/std.xcb
diff --git a/lib/R5RS.scm b/lib/R5RS.scm
@@ -542,10 +542,18 @@
    If two argumets are passed and they are not complex numbers
    it calulates Math.atan2 on those arguments."
   (if (and (null? rest) (complex? z))
-      (let ((iz (* +i z)))
-        (* (/ 1 +2i)
-           (log (/ (+ 1 iz)
-                   (- 1 iz)))))
+      (cond ((nan? z) +nan.0)
+            ((infinite? z)
+             (let ((atan (/ Math.PI 2)))
+               (if (< z 0)
+                   (- atan)
+                   atan)))
+            (else
+             ;; ref: https://youtu.be/d93AarE0lKg
+             (let ((iz (* +i z)))
+               (* (/ 1 +2i)
+                  (log (/ (+ 1 iz)
+                          (- 1 iz)))))))
       (let ((x z) (y (car rest)))
         (if (and (zero? (imag-part x))
                  (zero? (imag-part y)))

diff --git a/tests/numbers.scm b/tests/numbers.scm
@@ -1058,7 +1058,11 @@
         (t.is (atan 0.5 0.6) 0.6947382761967033)
         (t.is (atan -0.5 0.6) -0.6947382761967033)
         (t.is (atan 0.5 -0.6) 2.44685437739309)
-        (t.is (atan -0.5 -0.6) -2.44685437739309)))
+        (t.is (atan -0.5 -0.6) -2.44685437739309)
+
+        (t.is (atan +inf.0) 1.5707963267948966)
+        (t.is (atan -inf.0) -1.5707963267948966)
+        (t.is (atan +nan.0) +nan.0)))
 
 (test "numbers: should calculate odd? / even?"
       (lambda (t)