outline details from C18 annex F

1 files changed, 49 insertions, 0 deletions

diff --git a/src/math/atan2.c b/src/math/atan2.c
index c4c56a63..3b88b617 100644
--- a/src/math/atan2.c
+++ b/src/math/atan2.c
@@ -4,11 +4,60 @@
 #include "errno.h"
 #include "nonstd/assert.h"
 
+#include "M_PI.c"
+#include "M_PI_2.c"
+
 /** arc tangent **/
 TYPE TGFN(atan2)(TYPE y, TYPE x)
 {
+	int classy = fpclassify(y);
+	int classx = fpclassify(x);
 	ASSERT_NONZERO(x);
 
+	if (classy == FP_ZERO && classx == 0) {
+		if (signbit(x)) {
+			return copysign(M_PI, y);
+		} else {
+			return y;
+		}
+	}
+
+	if (classy == FP_ZERO) {
+		if (x < 0) {
+			return copysign(M_PI, y);
+		} else if (x > 0) {
+			return y;
+		}
+	}
+
+	if (classx == FP_ZERO) {
+		if (y < 0) {
+			return - M_PI_2;
+		} else if (y > 0) {
+			return M_PI_2;
+		}
+	}
+
+	if (classx == FP_INFINITE) {
+		if (classy == FP_INFINITE) {
+			if (signbit(x)) {
+				return copysign(3.0 * M_PI / 4.0, y);
+			} else {
+				return copysign(M_PI / 4.0, y);
+			}
+		} else if (y > 0) {
+			if (signbit(x)) {
+				return copysign(M_PI, y);
+			} else {
+				return copysign(0.0, y);
+			}
+		}
+	}
+
+	if (classy == FP_INFINITE && classx != FP_INFINITE) {
+		return copysign(M_PI_2, y);
+	}
+
 	if (y == 0 && x == 0) {
 		errno = EDOM; /* ARGUMENT(y) and ARGUMENT(x) are both LITERAL(0)) */
 		return TGHUGE;