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caml_ba_get_N treats char elements as signed #6523

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vicuna opened this issue Aug 28, 2014 · 3 comments

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commented Aug 28, 2014

Original bug ID: 6523
Reporter: @yallop
Assigned to: @mshinwell
Status: resolved (set by @mshinwell on 2014-08-29T10:52:14Z)
Resolution: open
Priority: urgent
Severity: block
Fixed in version: 4.02.0+dev
Category: otherlibs
Related to: #6064

Bug description

$ cat ba_char.ml
let b = Bigarray.(Array1.create char c_layout 1) in
let c = '\128' in
begin
b.{0} <- c;
assert (b.{0} = c)
end;;
print_endline "ok";
$ ocamlc unix.cma bigarray.cma ba_char.ml -o ba_char && ./ba_char
Fatal error: exception File "ba_char.ml", line 5, characters 2-8: Assertion failed

Native code is fine, since it uses bigarray intrinsics:

$ ocamlopt unix.cmxa bigarray.cmxa ba_char.ml -o ba_char && ./ba_char
ok

The top-level crashes, since it assumes char can't hold negative values:

$ ocaml
OCaml version 4.02.0+dev16-2014-08-21

#load "unix.cma";;

#load "bigarray.cma";;

let b = Bigarray.(Array1.create char c_layout 1);;

val b :
(char, Bigarray.int8_unsigned_elt, Bigarray.c_layout) Bigarray.Array1.t =

b.{0} <- '\128';;

  • : unit = ()

b.{0};;

Segmentation fault

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commented Aug 28, 2014

Comment author: @yallop

Similarly the (unspecified) comparison order has changed, since it reads the elements through a char*. Patch attached.

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commented Aug 29, 2014

Comment author: @mshinwell

Fixed in 4.02 (rev 15148).

@vicuna vicuna closed this Aug 29, 2014

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commented Aug 29, 2014

Comment author: @xavierleroy

Nitpick: owing to the use of the C 'char' type (instead of 'unsigned char'), char bigarray elements were treated EITHER as signed OR as unsigned depending on the platform. End of nitpick.

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