Add utility for aligning stuff up and down

align.hh

+#ifndef ALIGN_HH_
+#define ALIGN_HH_
+
+#include "types.hh"
+
+template <typename T>
+T align_down(T n, T alignment)
+{
+    return n & ~(alignment - 1);
+}
+
+template <typename T>
+T align_up(T n, T alignment)
+{
+    return align_down(n + alignment - 1, alignment);
+}
+
+template <class T>
+T* align_down(T* ptr, size_t alignment)
+{
+    auto n = reinterpret_cast<uintptr_t>(ptr);
+    n = align_down(n, alignment);
+    return reinterpret_cast<T*>(n);
+}
+
+template <class T>
+T* align_up(T* ptr, size_t alignment)
+{
+    auto n = reinterpret_cast<uintptr_t>(ptr);
+    n = align_up(n, alignment);
+    return reinterpret_cast<T*>(n);
+}
+
+#endif