Big integers are truncated

[ztlpn]

I am having trouble using bin_prot library with js_of_ocaml. The following code:

Printf.printf "Size: %d\n" (Bin_prot.Size.bin_size_int64 (Int64.of_int 0x8000))

when run in the browser produces Size: 9 instead of correct Size: 5. Here is the relevant block of bin_prot source code: https://github.com/janestreet/bin_prot/blob/master/lib/size.ml#L16-L22

js_of_ocaml compiler produces a bunch of warnings:

Warning: integer overflow: integer 0xffffffff truncated to 0xffffffff; the generated code might be incorrect.
Warning: integer overflow: integer 0x80000000 truncated to 0x80000000; the generated code might be incorrect.
Warning: integer overflow: integer 0x100000000 truncated to 0x0; the generated code might be incorrect.
Warning: integer overflow: integer 0x80000000 truncated to 0x80000000; the generated code might be incorrect.
Warning: integer overflow: integer 0x100000000 truncated to 0x0; the generated code might be incorrect.
Warning: integer overflow: integer 0x80000000 truncated to 0x80000000; the generated code might be incorrect.

and in this case the generated code is indeed incorrect. The most obvious solution is to get rid of big integers in the source code but it is in third-party library and thus not easily modifiable. Am I out of luck?

[ztlpn]

As a side note, printing hex representations of integers in the warnings is a bit misleading in this case because they are exactly the same (but integers themselves and their signed decimal representations differ)

[Drup]

Integers are not 64 bits in javascript, so yes, you will have to change bin_prot I think. Note that the way it's currently done in bin_prot could be considered a bug, given how hostile to cross-compilation (and js_of_ocaml) it is.

[samoht]

/cc @diml

[hhugo]

There are some work in progress to solve this inside core & co (including bin_prot).
janestreet/core_kernel#8.
The easiest workaround for now is to use a 32bit compiler opam switch 4.02.1+32bit

[hhugo]

error message improved by f39398b

[hhugo]

http://ocsigen.org/js_of_ocaml/2.8/manual/core_async_kernel