elm-uint64

64-bit unsigned integer using wrapping overflow.

import UInt64

-- `0 - 0xFF` wraps around to `0xFFFFFFFFFFFFFF01`
UInt64.sub UInt64.zero (UInt64.fromInt 0xFF)
    |> UInt64.toHexString
    --> "FFFFFFFFFFFFFF01"

-- ( 0xFFFFFFFFFFFFFFFF / 1e10, 0xFFFFFFFFFFFFFFFF % 1e10 )
UInt64.divMod UInt64.maxValue (UInt64.floor 1e10)
    |> Tuple.mapBoth UInt64.toFloat UInt64.toFloat
    --> ( 1844674407, 3709551615 )

UInt64.fromInt32s 0x11223344 0xAABBCCDD
    |> UInt64.rotateRightBy 20
    |> UInt64.toHexString
    --> "BCCDD11223344AAB"

Design Goals

Low-level

Includes relatively low-level functions. High-level functions using these low-level functions would then belong to other packages which depend on UInt64.

For example isPrime wouldn't belong to this package, but if someone needs add-with-carry or multiply-accumulate🢅 , those can be considered.

If you need a function which you think should be included, please create an issue🢅 mentioning use case for the function.

Fast

As fast as feasible, given the chosen implementation of three 24-bit unsigned integers. This goal is balanced with code complexity.

Safe Enough

Invalid arguments

Handling of invalid arguments is balanced with goal of speed. See Argument handling.

Testing

Every function, no matter how trivial, has at least one full-range fuzz test.

More tests are added as seemed necessary.

Performance

Here are some quick benchmark results. As usual I'm not interested in proper benchmarking, so take these with 2^64 grains of salt:

                                      runs / second
pow   : 64-bit number ^ 64-bit number: ~     40 000
pow   : 64-bit number ^ 251          : ~    300 000
divMod: 64-bit number / 40-bit number: ~  2 000 000
pow   : 64-bit number ^ 16           : ~  3 000 000
divMod: 64-bit number / 29-bit number: ~  5 000 000
add, sub, mul                        : > 10 000 000
bitwise shift/rotate by 1 bit        : ~ 20 000 000

Benchmarking was done 2020-06-19 with version 1.0.0, elm make --optimize, Elm 0.19.1, Firefox 68, Debian Linux and Core i5 3570K 3.4 GHz.

Some example benchmarks are included in benchmarks directory of source.

Modules

UInt64

malaire/elm-uint64/1.0.0