math: add align_up/down

Signed-off-by: Simon Rozman <simon@rozman.si>

include/stdex/math.hpp

@@ -67,6 +67,34 @@ namespace stdex
 		throw std::invalid_argument("add overflow");
 	}
 
+	///
+	/// Rounds number down and aligns it to have given number of lower bits zero.
+	///
+	/// \param a  Number to round down
+	/// \param n  Number of lower bits to be zero after rounding
+	///
+	/// \return The biggest number lower or equal to a that has n lower bits zero
+	///
+	inline constexpr size_t align_down(size_t a, int n)
+	{
+		const size_t mask = SIZE_MAX << n;
+		return a & mask;
+	}
+
+	///
+	/// Rounds number up and aligns it to have given number of lower bits zero. It throws on overflow.
+	///
+	/// \param a  Number to round up
+	/// \param n  Number of lower bits to be zero after rounding
+	///
+	/// \return The first number greater or equal to a that has n lower bits zero
+	///
+	inline constexpr size_t align_up(size_t a, int n)
+	{
+		const size_t mask = SIZE_MAX << n;
+		return add(a, ~mask) & mask;
+	}
+
 	///
 	/// Bitwise rotates left
 	///