Expand docs for bitshift operators

[simonbyrne]

No description provided.

[eschnett]

>> is not always signed; it is signed for signed types, and unsigned for unsigned types.

That is, unsigned types always shift in zeros from the left.

The result is not undefined for negative n; there is generally very little undefined behaviour in Julia. Instead, n is reinterpreted as unsigned number. (This could/should/will change, leading to an error instead in this case.)

[simonbyrne]

Good point: I hadn't noticed that the code in intrinsics.cpp used an unsigned comparison. However, that's not quite true: big(1) << -1 returns an error, not big(1) << unsigned(-1) (which would be huge).

[simonbyrne]

I've updated based on @eschnett's comments. I've left out the behaviour for n < 0 until #14516/#14791 is resolved.

[eschnett]

LGTM.

[tkelman]

where did T come from?

please run genstdlib here

[simonbyrne]

good catch.

Actually, should these be moved inline? If so, would they be better in int.jl or operators.jl?

[tkelman]

may as well move them inline, yeah. I think operators.jl has the most general signature, but don't think it matters too much

[hayd]

I feel like an example may help here, e.g.

julia> 3 << 2
12

julia> bits(3)
"0000000000000000000000000000000000000000000000000000000000000011"

julia> bits(12)
"0000000000000000000000000000000000000000000000000000000000001100"

but that may be a little too verbose?

[simonbyrne]

Good idea. The only problem is that the exact output will depend on the exact type of Int.

[KristofferC]

Could perhaps make it shorter and platform independent by specifying the int type:

julia> Int8(3) << 2
12

julia> bits(Int8(3))
"00000011"

julia> bits(Int8(12))
"00001100"

[simonbyrne]

@KristofferC that's a good idea, makes it much more readable.

[hayd]

Minor: I wonder if the example should go before the bigint note?

This is a big improvement, looks great!

[eschnett]

This is a good change.

I like it if functions contain pointers to other, related functions. You could add a "See also: >>, >>>" to the documentation of <<, and vice versa.

[tkelman]

incorrectly resolved conflict here? fieldoffsets was recently deprecated

[hayd]

Sorry, I figured that was intentional. PR to fix below/soon.