[erlang-questions] OTP float error on ARM

WS Dao <>
Thu Oct 16 08:09:47 CEST 2008


Oh.
so, which file should i patch, please?


2008/10/16 Bob Ippolito <>

> Well, the float type in Erlang binaries by itself is big endian, not
> native endian. This is a bug in Erlang.
>
> On Wed, Oct 15, 2008 at 8:59 PM, WS Dao <> wrote:
> > my shell output is:
> >
> > 4> <<1.0:64/float>>.
> > <<0,0,0,0,63,240,0,0>>
> >
> >
> > as Tony said, S3C2410/ARM920T CPU , double float is "Middle Endian"
> >
> > IEEE float:  12 34 AB CD
> > Middle Endian: AB CD 12 34
> >
> >
> > my toolchain doesn't support "-msoft-float" option.
> > [ ~]# arm-unknown-linux-gnu-readelf -h
> > /tmp/cross-compile/lib/erlang/erts-5.6.4/bin/beam
> > ELF Header:
> >   Magic:   7f 45 4c 46 01 01 01 61 00 00 00 00 00 00 00 00
> >   Class:                             ELF32
> >   Data:                              2's complement, little endian
> >   Version:                           1 (current)
> >   OS/ABI:                            ARM
> >   ABI Version:                       0
> >   Type:                              EXEC (Executable file)
> >   Machine:                           ARM
> >   Version:                           0x1
> >   Entry point address:               0x21f84
> >   Start of program headers:          52 (bytes into file)
> >   Start of section headers:          1346104 (bytes into file)
> >   Flags:                             0x2, has entry point, GNU EABI
> >   Size of this header:               52 (bytes)
> >   Size of program headers:           32 (bytes)
> >   Number of program headers:         6
> >   Size of section headers:           40 (bytes)
> >   Number of section headers:         31
> >   Section header string table index: 28
> >
> >
> > My platform doesn't support clock_gettime(CLOCK_MONOTONIC,&ts) ,
> > /erts/emulator/sys/unix/sys.c, so I can't use debian binary.
> >
> >
> >
> > 2008/10/15 Bob Ippolito <>
> >>
> >> There's code in io_lib_format.erl that does the default format floats,
> >> which assumes IEEE 754 floats. Perhaps the float<->binary code is
> >> broken on your platform, or your platform doesn't do IEEE 754?
> >>
> >> This is the code in io_lib_format (in R12B3 anyway, I don't have R12B4
> >> installed on this machine):
> >>
> >> mantissa_exponent(F) ->
> >>    case <<F:64/float>> of
> >>        <<_S:1, 0:11, M:52>> -> % denormalized
> >>            E = log2floor(M),
> >>            {M bsl (53 - E), E - 52 - 1075};
> >>        <<_S:1, BE:11, M:52>> when BE < 2047 ->
> >>            {M + ?BIG_POW, BE - 1075}
> >>    end.
> >>
> >> Does the output for this differ in your shell? If so, then your Erlang
> >> VM isn't doing the right thing when converting floats to binary...
> >>
> >> 1> <<1.0:64/float>>.
> >> <<63,240,0,0,0,0,0,0>>
> >>
> >>
> >> 2008/10/15 WS Dao <>:
> >> > I cross-compiled OTP R12B4 for my ARM9 platform (S3C2410, kernel
> 2.4.18)
> >> > When I run erl on arm, float error occurs:
> >> > # ./erl
> >> > Eshell V5.6.4  (abort with ^G)
> >> > 1> 3+5.
> >> > 8
> >> > 2> 3.0.
> >> > 0.
> >> >
> >> >
> 000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000005307579804
> >> > 3> 3.0+4.0.
> >> >
> >> >
> 0.00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000531405562
> >> > 4>
> >> >
> >> > My toolchain is gcc 3.4.5.  I'd wrote a c test program and
> cross-compile
> >> > it,
> >> > no float problems found.
> >> >
> >> > Any suggestion?
> >> >
> >> >
> >> > -dao
> >> > _______________________________________________
> >> > erlang-questions mailing list
> >> > 
> >> > http://www.erlang.org/mailman/listinfo/erlang-questions
> >> >
> >
> >
>
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