rand via scaled random integers

[milankl]

fixes #79

Question remains @oscardssmith: Why write (1)

BFloat16(Float32(rand(rng, UInt8)) * Float32(0x1.0p-8))

and not just (2)

rand(rng, UInt8) * BFloat16(0x1.0p-8)

?
From a precision perspective they are the same (no rounding errors in BFloat16 arithmetic because you exactly hit eps/2, eps, 3eps/2, n*eps/2 which are all perfectly representable) but in (1) the actual multiplication is hardcoded in Float32
which avoids the conversion from BFloat16(0x1.0p-8) to Float32 if BFloat16 is not natively supported, I believe? Meaning it's probably faster if bfloat16 is not natively supported. Whereas with (2) we would have the advantage that LLVM's bfloat type would decide what to do depending on the hardware meaning it would be faster on devices with bfloat16 support (as multiplication is then not done with Float32?)

[oscardssmith]

2 is better

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 66.84%. Comparing base (ee51ce2) to head (9ddc0a5).

Additional details and impacted files

@@            Coverage Diff             @@
##           master      #82      +/-   ##
==========================================
+ Coverage   66.66%   66.84%   +0.18%     
==========================================
  Files           3        3              
  Lines         186      184       -2     
==========================================
- Hits          124      123       -1     
+ Misses         62       61       -1     

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