1 files changed, 41 insertions, 0 deletions
diff --git a/src/math/atan2.c b/src/math/atan2.c
new file mode 100644
index 00000000..be5b9dd6
--- /dev/null
+++ b/src/math/atan2.c
@@ -0,0 +1,41 @@
+# define TGSOURCE "atan2.c"
+#include <math.h>
+#include "nonstd/tgmath.h"
+#include "errno.h"
+#include "nonstd/assert.h"
+
+/** arc tangent **/
+TYPE TGFN(atan2)(TYPE y, TYPE x)
+{
+	ASSERT_NONZERO(x);
+
+	if (y == 0 && x == 0) {
+		errno = EDOM; /* ARGUMENT(y) and ARGUMENT(x) are both LITERAL(0)) */
+		return TGHUGE;
+	}
+
+	if (0) {
+		errno = ERANGE; /* The result cannot be represented */
+		/* RETURN_FAILURE(CONSTANT(HUGE_VAL), A range error occurred); */
+		return TGHUGE;
+	}
+
+	TYPE ret = TGFN(tan)(y / x);
+	/* FIXME: quadrant */
+	/* RETURN_SUCCESS(a value in range `[-PI(), +PI()]'); */
+	return ret;
+}
+
+/***
+functions compute the principal value of the arc tangent of
+ARGUMENT(y)/ARGUMENT(x), using the signs of both to place the return value in
+the correct quadrant.
+***/
+
+/*
+IMPLEMENTATION(The value returned on a domain error, CONSTANT(HUGE_VAL))
+LINK(m)
+*/
+/*
+STDC(1)
+*/