1 files changed, 39 insertions, 0 deletions
diff --git a/Modules/_math.h b/Modules/_math.h
index 2285b64..b8477d2 100644
--- a/Modules/_math.h
+++ b/Modules/_math.h
@@ -23,3 +23,42 @@ _Py_log1p(double x)
 }
 
 #define m_log1p _Py_log1p
+
+/*
+   wrapper for atan2 that deals directly with special cases before
+   delegating to the platform libm for the remaining cases.  This
+   is necessary to get consistent behaviour across platforms.
+   Windows, FreeBSD and alpha Tru64 are amongst platforms that don't
+   always follow C99.  Windows screws up atan2 for inf and nan, and
+   alpha Tru64 5.1 doesn't follow C99 for atan2(0., 0.).
+*/
+
+static double
+_Py_atan2(double y, double x)
+{
+    if (isnan(x) || isnan(y))
+        return Py_NAN;
+    if (isinf(y)) {
+        if (isinf(x)) {
+            if (copysign(1., x) == 1.)
+                /* atan2(+-inf, +inf) == +-pi/4 */
+                return copysign(0.25*Py_MATH_PI, y);
+            else
+                /* atan2(+-inf, -inf) == +-pi*3/4 */
+                return copysign(0.75*Py_MATH_PI, y);
+        }
+        /* atan2(+-inf, x) == +-pi/2 for finite x */
+        return copysign(0.5*Py_MATH_PI, y);
+    }
+    if (isinf(x) || y == 0.) {
+        if (copysign(1., x) == 1.)
+            /* atan2(+-y, +inf) = atan2(+-0, +x) = +-0. */
+            return copysign(0., y);
+        else
+            /* atan2(+-y, -inf) = atan2(+-0., -x) = +-pi. */
+            return copysign(Py_MATH_PI, y);
+    }
+    return atan2(y, x);
+}
+
+#define m_atan2 _Py_atan2