Code review and speedup for Amaze Demosaic

rtengine/rt_math.h

@@ -78,5 +78,15 @@ inline const _Tp& max(const _Tp& a, const _Tp& b, const _Tp& c, const _Tp& d)
 {
     return std::max(d, std::max(c, std::max(a, b)));
 }
+
+template<typename _Tp>
+inline const _Tp intp(const _Tp a, const _Tp b, const _Tp c) {
+    // calculate a * b + (1 - a) * c
+    // following is valid:
+    // intp(a, b+x, c+x) = vintpf(a, b, c) + x
+    // intp(a, b*x, c*x) = vintpf(a, b, c) * x
+    return a * (b-c) + c;
+}
+
 }
 #endif