OK, I've added that fix to my copy and done some more testing.
I think there are two more issues, for ranges that span from neg to pos:
-
It returns both
-0and+0, as if they were separate values, leading to zero being twice as probable as it should be. -
It will never return the lowest value(s).
Unless there's something wrong with my Float8 implementation.
I have this program:
func test2() {
var prng = WyRand()
let range = -Float8(0.25) ... Float8(0.25)
var hist = [UInt8 : UInt64]()
for _ in 0 ..< 1024*1024*16 {
let f = Float8.uniformRandom(in: range, using: &prng)
precondition(f >= range.lowerBound)
precondition(f <= range.upperBound)
hist[f.bitPattern, default: 0] &+= 1
}
for (v, c) in hist
.map( { (k, v) in (Float8(bitPattern: k), v) })
.sorted(by: { $0.0 < $1.0 })
{
print(v.leftPadded(to: 12), c.leftPadded(to: 12))
}
}
which prints:
-0.21875 508187
-0.203125 509107
-0.1875 508170
-0.171875 508190
-0.15625 509122
-0.140625 506923
-0.125 508131
-0.1171875 254522
-0.109375 254622
-0.1015625 253875
-0.09375 254150
-0.0859375 254467
-0.078125 255003
-0.0703125 254489
-0.0625 253645
-0.05859375 126968
-0.0546875 126530
-0.05078125 127365
-0.046875 127228
-0.04296875 126859
-0.0390625 127214
-0.03515625 126985
-0.03125 127250
-0.029296875 63996
-0.02734375 63541
-0.025390625 63285
-0.0234375 64074
-0.021484375 63689
-0.01953125 63317
-0.017578125 63752
-0.015625 63303
-0.013671875 63612
-0.01171875 63768
-0.009765625 63651
-0.0078125 63658
-0.005859375 63417
-0.00390625 63388
-0.001953125 63283
0.0 63822
-0.0 63690
0.001953125 63852
0.00390625 63022
0.005859375 63883
0.0078125 63613
0.009765625 63336
0.01171875 63880
0.013671875 63492
0.015625 63690
0.017578125 63412
0.01953125 63818
0.021484375 63175
0.0234375 64183
0.025390625 63378
0.02734375 63788
0.029296875 63606
0.03125 127193
0.03515625 126783
0.0390625 126845
0.04296875 127229
0.046875 127361
0.05078125 127118
0.0546875 126800
0.05859375 127299
0.0625 254559
0.0703125 254697
0.078125 253568
0.0859375 254446
0.09375 253203
0.1015625 253773
0.109375 254352
0.1171875 254890
0.125 508204
0.140625 507725
0.15625 509499
0.171875 509270
0.1875 508547
0.203125 508257
0.21875 508844
0.234375 507503
0.25 1014875
Note that the expected first two values -0.25 and -0.234375 are missing, and that both -0 and 0 are there as separate values.