Extracting a bit of code:
/* Computes the mod operator on the two numbers, defined as
``mod(x,y) = x - y * floor(x / y)``.
The return value has the same type as `x`.
*/
proc mod(x: real(?w), y: real(w)): real(w) {
// This codes up the standard definition, according to Wikipedia.
// Is there a more efficient implementation for reals?
return x - y*floor(x/y);
}
Using a Wikipedia reference in intriguing. They quote a reference
from Knuth as the source of the slgorithm.
Anyway, the above is basically
n = floor(x/y)
return x - y * n
I think 'floor' is really just
Directed Rounding toward negative infinity
Both the C99 and D implementations, both of which are called 'fmod' and
rely on the ISO specification, use
Directed Rounding - Tied Away From Zero
Is there a good reason for Chapel to be different? I do note that the ISO
document does not mandate the rounding mode although I should go back and
check and see if there are updates. While it is a big ask to argue against
the ideas of Donald Knuth, nobody has really run with his idea of using
'floor' as the basis for the computation of 'n' above, But again, why be
different.
There is also a 'REM' function (C99=remainder) in the ISO document which
does mandate the use in the algorithm of the rounding mode as.
Round - Tied to Even
Both C99 and D have this. Chapel does not.
Regards - Damian
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