4.4 Variable Conventions

MPRIA functions expect output arguments before input arguments. This general rule, which is inherited from the GNU MP library, is based on an analogy with the assignment operator.

As a matter of fact, the analogy has been pushed further by allowing to use the same variable for both input and output in the same expression; this extension of the general rule is also inherited from the GNU MP library. For example, the square function, mpri_sqr, can be used as follows:

mpri_sqr (x, x);

what computes the set of squares of every rational number belonging to x and puts the results back in x.

As for MP variables, MPRIA variables must be initialised once before any assignment and may be cleared out after use. A (MP or) MPRIA variable should be initialised only once, or at least be cleared out between each initialisation. After such a variable has been initialised, it can be assigned numerous times; it will have the same allocated space during all its lifetime.

For efficiency reasons, avoid excessive initialising and clearing out: as a rule of thumb, initialise near the beginning of an application and clear out near its ending; better still, implement workspaces or garbage collections to pass and reuse these variables all along the computing process.