Something that I have been able to avoid is how the modulus operator %
is implemented in different programming languages.
While trying to implement and learn some cryptographic algorithms in .NET (F# mostly of course) I got into some trouble with the modulus operator.
Here is a clear example:
dotnet fsi
> -10 % 3;;
val it: int = -1
python3
>>> -10 % 3
2
After some research I found this blog post, What's the difference? Remainder vs Modulus by Eric Lippert.
The % operator does not give the canonical modulus, it gives the remainder.
So the thing is that some programming languages are implementing the % operator either as a canonical modulus or as the remainder operation.
In this case I want the canonical one and not the remainder that .NET uses.
To keep going with my cryptographic explorations in F#, I used this implementation which is inspired by this issue, Proposal: New operator %% for canonical Modulus operations, from the C# Language Design repository.
let (%%) a b =
let c = a % b
if (c < 0 && b > 0) || (c > 0 && b < 0) then
c + b
else
c
Now I can use it like this.
dotnet fsi
> -10 %% 3;;
val it: int = 2
Happy modulus!
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