about DivideAndRemainder functionnality
Paul Zimmermann
Paul.Zimmermann at loria.fr
Mon Jan 28 15:19:31 CET 2008
> Hello,
> I'm not a expert with mathematic, so I come to you because I need to
> find the divider and the remainder of 2 numbers, like the Java
> BigInteger.DivideAndRemainder() do. I do not know wich GMP's divide
> function to use :
>
> To get the remainder I think I've just to call mpz_mod() but I do not
> know the divide function : cdiv or fdiv or tdiv or another ?
>
> Thanks for your help
> Cyrille.
mpz_mod returns the classical remainder, i.e., in [0, |D|-1].
The difference between the cdiv/fdiv/tdiv is clearly explained in the manual:
* `cdiv' rounds Q up towards +infinity, and R will have the
opposite sign to D. The `c' stands for "ceil".
* `fdiv' rounds Q down towards -infinity, and R will have the
same sign as D. The `f' stands for "floor".
* `tdiv' rounds Q towards zero, and R will have the same sign
as N. The `t' stands for "truncate".
For a positive divisor D, mpz_mod thus corresponds to fdiv. Note that if you
want to be sure that N=Q*D+R, it is better to use the mpz_?div_qr functions,
which return both quotient and remainder.
Paul Zimmermann
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