maths: add sinc functions

maths.hpp

@@ -193,16 +193,21 @@ to_radians [[gnu::pure]] (T degrees)
 }
 
 
-//-----------------------------------------------------------------------------
+//! Normalised sinc function
-constexpr float
+template <typename T>
-to_radians [[gnu::pure]] (float degrees) {
+constexpr T
-    return degrees / 180 * static_cast<float> (PI_f);
+sincn [[gnu::pure]] (T x)
+{
+    return std::sin (constants<T>::PI * x) / (constants<T>::PI * x);
 }
 
 
-constexpr double
+//! Unnormalised sinc function
-to_radians [[gnu::pure]] (double degrees) {
+template <typename T>
-    return degrees / 180 * PI_d;
+constexpr T
+sincu [[gnu::pure]] (T x)
+{
+    return std::sin (x) / x;
 }