re-evaluate/remove Random.UnsafeView

[JeffBezanson]

I just noticed the Random stdlib has an UnsafeView type for filling arrays. With the new layout optimizations, this should no longer be necessary. We should try using the normal SubArray type for this. If it's still too slow/complex, then at least the type can be made safe by holding the underlying array directly instead of a Ptr.

[DebadityaPal]

I would like to work on this issue.

[DebadityaPal]

In the file stdlib/Random/src/RNGs.jl, there exists a line of code(Line 524)

GC.@preserve r unsafe_copyto!(A.ptr, pointer(r.vals, r.idxF+1), m)

it looks like some values are being copied into A which is an UnsafeView, however the source of the values are r.idfX+1 which is one element after the r.vals vector ends. I am a bit confused as to why values are being copied from a memory location after the end of the vector. Could you please guide me a bit?

[rfourquet]

the source of the values are r.idfX+1 which is one element after the r.vals vector ends.

Why do you think so? r.idxF acts as a pointer into r.vals and indicates how many values in r.vals have been consumed. So here r.idxF + 1 points at the first non-consumed values, and m is the number of non-consumed values.

[DebadityaPal]

oh okay, thanks for the explanation, now it makes sense.

[DebadityaPal]

A lot of the times the Structure of UnsafeView is being used to typecast the data in the memory for example by putting a Array{bool} into an UnsafeView{Int128} like in Line 697 of stdlib/Random/src/RNGs.jl. Are there any such explicit typecasting functions for SubArrays? My reading of the docs were inconclusive. I have tried using the Base.convert function but it fails to do these kinds of SubArray conversions.