Reland r10908 (Ensure consistent result of transcendental function0.)

src/platform.h

Index: src/platform.h
diff --git a/src/platform.h b/src/platform.h
index 38e633a38081e155744d9e1942c9eee8fc73827f..ccb4109b22b500ae35ca8adf4c64601e8b23d716 100644
--- a/src/platform.h
+++ b/src/platform.h
@@ -96,6 +96,12 @@ class Mutex;
 double ceiling(double x);
 double modulo(double x, double y);
 
+// Custom implementation of sin, cos, tan and log.
+double fast_sin(double input);
+double fast_cos(double input);
+double fast_tan(double input);
+double fast_log(double input);
+
 // Forward declarations.
 class Socket;