functions must act as pure functions

Functions defined in pugs are mean to be mathematical functions. These are pure functions: no data should change during function application. That is

• parameters are unchanged
• used global data are constant
• called C-functions, such as cmath functions for instant, must not modify arguments (C-function arguments must be const.

These three rules are not ensured by now, which does not correspond to the definition of these functions. Moreover violating these constrains can lead to unexpected behavior or even more to undefined behavior.