Fix float bias towards high exponents (#3463)

[younghoonk17]

fix for #3463

[myuwono]

I wonder if that's right? This would transform the float into an int, i.e. 3.0f would become 3 instead of 1077936128.

In theory we probably want to get the floats in the bits representations instead. Floats have a Float.toBits() extensions that should do that if I remember correctly. If that's right roundtripping that should work.

Float.fromBits(it.random.nextInt(min.toBits(), max.toBits()))

additionally, there's also another Arb.Companion.float in this file that is still using random.nextDouble. That would need to have the same logic.

[myuwono]

Ah thinking about this again.. i think we need to also think of the exponent because I'm not sure if currently it will generate the right float.. I wonder if there is a better way for us to do this. One thing that comes to mind would be to keep using double random, with some configurable probability of sampling from -minFloat and +minFloat if the arguments are in the range. Or perhaps utilising the edgecase random function to do that.

[younghoonk17]

Hey @myuwono I think this is the only way, I can't think of any elegant way of doing this except this

   val sign = it.random.nextInt(0, 2)
   val exponent = it.random.nextInt(0, 256)
   val mantissa = it.random.nextBits(23)
   val bits = (sign shl 31) or (exponent shl 23) or mantissa
   Float.fromBits(bits)

I also found a new way to draw the graph better

   test("draw distribution graph") {
      fun exponent(value: Float): Int {
         if (value == 0f) {
            return Int.MIN_VALUE
         }
         val bits = java.lang.Float.floatToIntBits(value)
         val exp = (bits shr 23) and 0xff
         return exp - 127
      }

      val generatedFloat = Arb.Companion.numericFloat(Float.MIN_VALUE, Float.MAX_VALUE * 100)
         .generate(RandomSource.seeded(1235), EdgeConfig(0.0))
         .take(1_000_000)
         .map { it.value}
         .groupBy{ number ->
            exponent(number)
         }
         .toSortedMap()

      fun intToGraph(count: Int): String{
         val stringNum = ceil(count.toDouble()/100)
         var result = ""
         (1..stringNum.toInt()).forEach {
            result += '-'
         }
         return result
      }

      generatedFloat.forEach {
         println("Exponent ${it.key} count ${intToGraph(it.value.count())} ")
      }
   }

[sksamuel]

@younghoonk17 can you fix the tests then we can merge. Thanks!