What is also interesting is that negative (-4 or -8) offsets are already used. The pointer actually points to the first byte of the data, but there is a header

What is also interesting is that negative (-4 or -8) offsets are already used. The pointer actually points to the first byte of the data, but there is a header located before the data which tells you how long the data is and some other runtime info used by the GC. +------------+------------+------------+------------+ - - - | header | data[0] | data[1] | data[2] | +------------+------------+------------+------------+ - - - ^ pointer (The real data part can be all kinds of things including stuff opaque to the GC like strings). I'm still a bit unconvinced that swapping the sense of pointers vs ints is useful for OCaml, as it would be a massive change with no current evidence base. It seems better to me to work on better compiler optimizations so that integers can be kept in registers with their true value more often.