Band Limited ImPulse generator. All harmonics have equal amplitude. This is the equivalent of 'buzz' in MusicN languages.
Synth-O-Matic (1990) had an impulse generator called blip, hence that name here rather than 'buzz'.
It is improved from other implementations in that it will crossfade in a control period when the number of harmonics changes, so that there are no audible pops. It also eliminates the divide in the formula by using a 1/sin table (with special precautions taken for 1/0). The lookup tables are linearly interpolated for better quality.
Frequency in Hertz.
Number of harmonics. This may be lowered internally if it would cause aliasing.