Arbitrary[Double] distribution is borken

[benhutchison]

Scalacheck is using a flawed method [https://github.com/rickynils/scalacheck/blob/master/src/main/scala/org/scalacheck/Arbitrary.scala#L105] to generate Arbitrary Double values. Currently, it basically generates 3 number "archetypes": +1E307, 0.0, and -1E307. Because it is using a uniform distribution with endpoints at +/- E307, the chance of it generating any values in a everyday range (say +/- 1000) is infinitesimally small.

A good solution IMO is to use a log-uniform distribution, ie one where log(value) is uniformly distributed, not the values themselves. This can be done by generating the mantissa and the exponent separately from uniform distributions.

[ummels]

+1