+
+ // Wondering whether the modification of the df vector
+ // using a char* pointer and pointer arithmetric was safe,
+ // I looked it up...
+ //
+ // http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2007/n2369.pdf tells me:
+ //
+ // 23.2.5 Class template vector [vector]
+ //
+ // [...] The elements of a vector are stored contiguously,
+ // meaning that if v is a vector<T,Allocator> where T is
+ // some type other than bool, then it obeys the identity
+ // &v[n] == &v[0] + n for all 0 <= n < v.size().
+ //