OCaml Basics

OCaml integers range from 2⁶² to 2⁶² − 1 on modern platforms. They are implemented with 64-bit machine words, which is the size of a register on 64-bit processor. But one of those bits is "stolen" by the OCaml implementation, leading to a 63-bit representation. That bit is used at run time to distinguish integers from pointers. For applications that need true 64-bit integers, there is an Int64 module in the standard library. And for applications that need arbitrary-precision integers, there is a separate Zarith library. But for most purposes, the built-in int type suffices and offers the best performance. (Clarkson 2025, 33)