qiStepGain property
Maps normalised buffer fullness (bufferBits / windowBits) to qi
units. With the default of 16.0, a buffer that has overshot by one
full window worth of bits raises qi by 16 steps — enough to span
most of the minQi..maxQi range from a startQi mid-point as
fullness saturates at the ±2-window clamp inside update.
Implementation
final double qiStepGain;