Q Value Handling

The q value expresses the priority of a URI within a set of URIs (Contact header field in the same SIP message or dset array in ser. The higher is the q value of a URI the higher is the priority of the URI.

The q value is usually expressed as a floating point number with limited number of decimal digits, for example 0.346. RFC3261 allows 0-3 decimal digits.

To speed things up we represent the q value as integer number, it is then easier to handle/print the value. To convert float into integer we multiply the q value by 1000, i.e. (float)0.567 == (int)567. In the opposite direction, values higher or equal to 1000 are converted to 1.0 and values below or equal to 0 are converted to 0.

Value Q_UNSPECIFIED (which is in fact -1) has a special meaning, it means that the q value is not known and the parameter should not be printed when printing Contacts, implementations will then use implementation specific pre-defined values.