V: Negative modulo is computing wrong

[x8-ball]

V version: 0.1.11
OS: Parrot/Debian

What did you do?
Tried to use modulo to stay in positive boundaries f.e. for arrays
a := -5 %3

What did you expect to see?
a := -5 %3
print('$a')

1

What did you see instead?
a := -5 %3
print('$a')

-2

I guess it just computed the number as it were positive.

[medvednikov]

Interesting, running it with C/Go returns -2, running it with Python returns 1.

So I guess different languages have different ways to handle negative modulos.

[ciubotaru]

Since C99, '%' clearly means 'remainder', not 'modulo'.

-5 / 3 yields -1, because division is truncated towards zero, not towards the smaller integer.

-5 % 3 yields -2, because (-5) - (3*(-1)) = -2

In Python, '%' means 'modulo'.

[whoizit]

[ciubotaru]

Ah, yes, for modulo there is a library function called 'modf()' in C.

[whoizit]

https://en.wikipedia.org/wiki/Modulo_operation

[medvednikov]

V's behavior will be the same as in Go and C.

math.modf will be added once functions can return multiple values.