sample ratio implementation: why we need CalculateThreshold?

[neopaf]

#136

Friends, please shed some light on necessity of CalculateThreshold

It moves us from double to int64 space, which is sometimes good.

But is it really necessary in this case?

What is wrong with converting trace_id to ratio and using it directly, without double-to-int magic?

//  if (CalculateThresholdFromBuffer(trace_id) <= threshold_)
  if (CalculateRatioFromBuffer(trace_id) <= ratio_)

[marcalff]

No reason in particular.

Any PR that improves runtime performances is welcome.

[neopaf]

Marc, I would like to figure out the reasons it was that way originally.
Looks very not-obvious.

Usually, that's a manifest of pain ;)

[neopaf]

@nholbrook Nick, was this your code and do you remember the background?