This library provides two new integer types, Optint.t and Int63.t, which guarantee efficient representation on 64-bit architectures and provide a best-effort boxed representation on 32-bit architectures.
The standard Int32.t and Int64.t types provided by the standard library have the same heap-allocated representation on all architectures. This consistent representation has costs in both memory and run-time performance.
On 64-bit architectures, it's often more efficient to use the native int directly. This library provides types to do exactly this:
Optint.t: an integer containing at least 32 bits. On 64-bit, this is an immediate integer; on 32-bit, it is a boxed 32-bit value. The overflow behaviour is platform-dependent.Int63.t: an integer containing exactly 63 bits. On 64-bit, this is an immediate integer; on 32-bit, it is a boxed 64-bit integer that is wrapped to provide 63-bit two's complement semantics. The two implementations are observationally equivalent, modulo use of Marshal and Obj.In summary:
Integer type | 32-bit representation | 64-bit representation | Semantics |
|---|---|---|---|
| 31-bit immediate ✅ | 63-bit immediate ✅ | Always immediate |
| 32-bit boxed ❌ | 64-bit boxed ❌ | Exactly word size |
| 32-bit boxed ❌ | 32-bit boxed ❌ | Exactly 32 bits |
| 64-bit boxed ❌ | 64-bit boxed ❌ | Exactly 64 bits |
| 32-bit boxed ❌ | 63-bit immediate ✅ | At least 32 bits |
| 64-bit boxed ❌ | 63-bit immediate ✅ | Exactly 63 bits |
These new types are safe and well-tested, but their architecture-dependent implementation makes them unsuitable for use with the Marshal module. Use the provided encode and decode functions instead.