Re:Uncle Bob and Silver Bullets (2017)
by Gordonjcp on Monday July 04, 2022 @07:36PM
(#31982805)
> my pet peeve is that operator== is even defined for floats
I fixed two bugs at once in a softsynth caused by this stupidity. In the envelope generator code, which loosely modelled the ADSR circuit in a synth which charges and discharges a capacitor, there was an integrator implemented like `env = ((target - env) * timeconstant) + env`. The `target` value was set to 1 to allow the "capacitor" to "charge" at a rate set by `timeconstant`, and when it reached the top it would be flipped to 0 and `timeconstant` changed to the decay rate.
It failed about one go in ten, with some fudges to set `timeconstant` in odd values. It turns out that they detected the "capacitor fully charged" state with something like `if (env == 0.999) { dostuff(); }` and for some values of `env` and `timeconstant` it might never hit *exactly* 0.999 if you got it exactly wrong.
It was logically wrong (detect a precise float value) and functionally wrong (envelopes switch over when the cap is about 2/3 charged). Changing the "flip over" condition to something more like `if (env > 0.999)` and changing the maximum value of `target` to 1.5 (mimicking a circuit running off 15V and trying to it a 10V output, like a real analogue synth) cured all its problems.
Well, all its *envelope* problems. There were more, but they get into scary discussions of poles and zeroes and negative frequencies, and you don't want that at this time of night.
I fixed two bugs at once in a softsynth caused by this stupidity. In the envelope generator code, which loosely modelled the ADSR circuit in a synth which charges and discharges a capacitor, there was an integrator implemented like `env = ((target - env) * timeconstant) + env`. The `target` value was set to 1 to allow the "capacitor" to "charge" at a rate set by `timeconstant`, and when it reached the top it would be flipped to 0 and `timeconstant` changed to the decay rate.
It failed about one go in ten, with some fudges to set `timeconstant` in odd values. It turns out that they detected the "capacitor fully charged" state with something like `if (env == 0.999) { dostuff(); }` and for some values of `env` and `timeconstant` it might never hit *exactly* 0.999 if you got it exactly wrong.
It was logically wrong (detect a precise float value) and functionally wrong (envelopes switch over when the cap is about 2/3 charged). Changing the "flip over" condition to something more like `if (env > 0.999)` and changing the maximum value of `target` to 1.5 (mimicking a circuit running off 15V and trying to it a 10V output, like a real analogue synth) cured all its problems.
Well, all its *envelope* problems. There were more, but they get into scary discussions of poles and zeroes and negative frequencies, and you don't want that at this time of night.