Initial implementation of lerp

include/ccmath/detail/lerp.hpp

@@ -10,5 +10,40 @@
 
 namespace ccm
 {
+ namespace 
+ {
+ namespace impl
+ {
+ template <typename Real>
+ inline constexpr Real lerp_impl(Real a, Real b, Real dt)
+ {
+ if ((a <= 0 && b >= 0) || (a >= 0 && b <= 0))
+ {
+ return dt * b + (1 - dt) * a;
+ }
+
+ if (dt == 1)
+ {
+ return b;
+ }
+
+ const Real x = a + dt * (b - a);
+ if ((dt > 1) == (b > a))
+ {
+ return b < x ? x : b;
+ }
+ else
+ {
+ return x < b ? x : b;
+ }
+ }
+ }
+ }
 
+ template <typename T>
+ inline constexpr T lerp(T a, T b, T t)
+ {
+ // TODO: Implement promotion and edge cases. 
+ return lerp_impl(a, b, t);
+ }
 } // namespace ccm