An efficient 64-bit integer with correct overflow.

Bitwise operators in javascript can only use 32 bits. Sometimes, external protocols use 64-bit integers. This package implementes such integers with "correct" overflow behavior.

This is a low-level package focussed on speed. The 64-bit integers are represented as a 2-tuple of 32-bit numbers. There are helpers for conversion to string and elm/bytes Bytes.

import Int64 

Int64.add (Int64.fromInt 42) (Int64.fromInt 10)
    |> Int64.toUnsignedString
    --> "52"

Int64.subtract (Int64.fromInt 10) (Int64.fromInt 42)
    |> Int64.toSignedString
    --> "-32"

Int64.xor 
    (Int64.fromInt32s 0xDEADBEEF 0xBAAAAAAD) 
    (Int64.fromInt 42)
    |> Int64.toHex
    --> "deadbeefbaaaaa87"

Performance is roughly half for subtraction, addition and the bitwise operators. That is great considering int64 is really two 32-bit integers, so we're doing operations twice.

This package is extensively tested with fuzz tests. Nonetheless, the logic is extremely tricky, so there might still be bugs.

1. Int64 -> Int

   This is unsafe, because Int cannot store all the information of a Int64. If you think the conversion is safe for you, use:

   Int64.fromInt 42
       |> Int64.toSignedString
       |> String.toInt
       --> Just 42

2. String -> Int64

   And by extension converting 64-bit integers in e.g. JSON into Int64. This is tricky to implement, but PRs are welcome!

3. Multiplication, integer division, modulo

   Would be nice to have, again PRs are welcome!