1 files changed, 18 insertions, 0 deletions
diff --git a/missing/isinf.c b/missing/isinf.c
new file mode 100644
index 0000000000..0297efdfd4
--- /dev/null
+++ b/missing/isinf.c
@@ -0,0 +1,18 @@
+static double zero()	{ return 0.0; }
+static double one()	{ return 1.0; }
+static double inf()	{ return one() / zero(); }
+
+int
+isinf(n)
+    double n;
+{
+    static double pinf = 0.0;
+    static double ninf = 0.0;
+
+    if (pinf == 0.0) {
+	pinf = inf();
+	ninf = -pinf;
+    }
+    return memcmp(&n, &pinf, sizeof n) == 0
+	|| memcmp(&n, &ninf, sizeof n) == 0;
+}