package optint

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Abstract type on integer between x64 and x86 architecture

Install

Dune Dependency

Authors

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Sources

optint-v0.0.5.tbz
sha256=774901af130eacc08e30ae43e9a18c926f284c22e3c66c2ff95e74648fbedf26
sha512=fe5762ee7a1a08c7b389fbef9188f8a59c40bb8e19535cec1661a789f973338d5b6d4b30c1869e089282242efa63bfc86c1fb15224b47c05cb5277971aa14a35

README.md.html

Optint - Abstract integer types between x64 and x86 architectures

This library provides two new integer types, Optint.t and Int63.t, which guarantee efficient representation on x64 architectures and provide a best-effort boxed representation on x86 architectures.

Goal

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.t directly, and fallback to the boxed representations on 32-bit architectures. This library provides types to do exactly this:

  • Optint.t: an integer containing at least 32 bits. On 64-bit machines, this is an immediate integer; on 32-bit machines, it is a boxed 32-bit value. The overflow behaviour is platform-dependent.

  • Int63.t: an integer containing exactly 63 bits. On 64-bit machines, this is an immediate integer; on 32-bit machines, 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 x86 representation x64 representation Semantics
Stdlib.Int.t 31-bit immediate ✅ 63-bit immediate ✅ Always immediate
Stdlib.Nativeint.t 64-bit boxed ❌ 32-bit boxed ❌ Exactly word size
Stdlib.Int32.t 32-bit boxed ❌ 32-bit boxed ❌ Exactly 32 bits
Stdlib.Int64.t 64-bit boxed ❌ 64-bit boxed ❌ Exactly 64 bits
Optint.t (new) 32-bit boxed ❌ 63-bit immediate ✅ At least 32 bits
Int63.t (new) 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.

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