[erlang-questions] Binaries problem

[Francesco Pierfederici]

Hi Per,

Thank you for your help: now everything works and I am happy again :-)


Cheers,
Francesco


On 5/2/07, Per Gustafsson <per.gustafsson@REDACTED> wrote:
> Francesco Pierfederici wrote:
> > Hi,
> >
> > I have encountered a problem with handling binaries and I do not know
> > what the cause might be. In a nutshell, I seem to be unable to
> > assemble binaries larger than 2097149 bytes:
> >
> > -module(test).
> > -export([test/2]).
> >
> >
> > test(FileName, NumBytes) ->
> >     {ok, Fd} = file:open(FileName, [raw, binary]),
> >     {ok, Data} = file:read(Fd, NumBytes),
> >     file:close(Fd),
> >
> >     NumRestBits = NumBytes * 8 - 1,
> >     <<Bit:1, Rest:NumRestBits>> = Data,
> >
> >     NewData = <<Rest:NumRestBits, 0:1>>,
> >     ok.
> >
> >
> > And then
> >
> > inanna> erl
> > Erlang (BEAM) emulator version 5.5.4 [source] [async-threads:0] [hipe]
> > [kernel-poll:false]
> >
> > Eshell V5.5.4  (abort with ^G)
> > 1> c(test).
> > ./test.erl:11: Warning: variable 'Bit' is unused
> > ./test.erl:13: Warning: variable 'NewData' is unused
> > {ok,test}
> > 2> test:test('/Users/fpierfed/Desktop/software/xcode_2.4.1_8m1910_6936315.dmg',
> > 2097148).
> > ok
> > 3> test:test('/Users/fpierfed/Desktop/software/xcode_2.4.1_8m1910_6936315.dmg',
> > 2097149).
> >
> > =ERROR REPORT==== 1-May-2007::16:33:57 ===
> > Error in process <0.37.0> with exit value:
> > {badarg,[{test,test,2},{erl_eval,do_apply,5},{shell,exprs,6},{shell,eval_loop,3}]}
> >
> > ** exited: {badarg,[{test,test,2},
> >                     {erl_eval,do_apply,5},
> >                     {shell,exprs,6},
> >                     {shell,eval_loop,3}]} **
> >
> >
> > Is this a bug? Am I doing something wrong?
> >
> > Thank you!
> > Francesco
> >
> > P.S. I am running this on a Mac OS X box using both R11B-4 and the
> > latest snapshot (R11B_2007-05-01) with identical results.
> > P.P.S. I get the same results with different files so there seems to
> > be nothing peculiar about the 900+ MB XCode file.
> > _______________________________________________
> > erlang-questions mailing list
> > erlang-questions@REDACTED
> > http://www.erlang.org/mailman/listinfo/erlang-questions
>
> I think that the problem you are running in to is that you are creating
> an integer that is too big for the erlang runtime system. I'm not sure
> exactly where this limit is but it should be in the order of what you
> are creating.
>
> You can sidestep this problem (and have a much more efficient
> implementation by writing:
>
>
> test(FileName, NumBytes) ->
>    {ok, Fd} = file:open(FileName, [raw, binary]),
>    {ok, Data} = file:read(Fd, NumBytes),
>    file:close(Fd),
>
>    <<Bit:1, Pad:7, Rest/binary>> = Data,
>
>    NewData = <<Pad:7,Rest/binary, 0:1>>,
>    ok.
>
> Or if you use the following compiler option: [bitlevel_binaries]
>
> test(FileName, NumBytes) ->
>    {ok, Fd} = file:open(FileName, [raw, binary]),
>    {ok, Data} = file:read(Fd, NumBytes),
>    file:close(Fd),
>
>    <<Bit:1, Rest/bitstr>> = Data,
>
>    NewData = <<Rest/bitstr, 0:1>>,
>    ok.
>
> Of course this syntax is only experimental.
>
> Per
>