integer division rounding

Michael Lunnay mlunnay at
Tue Jul 17 04:17:38 EDT 2001

Which is 'mathematically' correct then? I am doing some graphics coding and
while my maths background is shakey (re-learning it all as I go along) I
would like to match the work I am learning from.
Should I do all floating point division and then use so as
to match C code?


> > Why does an integer division resulting in a negative round down
,e.g -0.5
> > => -1, while C and rounds up ,e.g -0.5 => 0. Is this
> > purposful error(?), or an oversight?
> Purposeful.  This way, 0 <= m%n < n and (m/n)*n + m%n = m.
> The other choice (round toward 0) maintains the invarient -(m/n) = (-m/n).
> Much as we would like, we cannot make all three invarients true at once
> negative quotients.
> Terry J. Reedy

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