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 ?
>
> 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
```