Rounding up and down to nearest multiple

rounding.java

/** round n down to nearest multiple of m */
long roundDown(long n, long m) {
    return n >= 0 ? (n / m) * m : ((n - m + 1) / m) * m;
}

/** round n up to nearest multiple of m */
long roundUp(long n, long m) {
    return n >= 0 ? ((n + m - 1) / m) * m : (n / m) * m;
}

I needed to round up or down to the nearest n:

(i % n) > n/2) ? i + n - i%n : i - i%n

@paulca neat

@aslakhellesoy — It's actually one of my favorite pieces of code from the last 5 years! Credit actually goes to @destraynor for the logic.

@paulca yes, very elegant. I love small snippets like that. Thanks for sharing!

It seems roundUp is the inverse of roundDown so roundUp could be:
-1 * roundDown(-n, m)
Not sure that makes things clearer though

Who cares about clarity for this kind of code! It's just compact math :-) I'll do that refactoring tomorrow. Well spotted!

👍

Note that this code only works if all values are integer/long (using float/double gives wrong results in some cases).