Problem with 64 bit FP under ARM

Matthias Lang <>
Sat Aug 23 10:55:01 CEST 2003


Martin Sandiford writes:

 > (Running under Linux on x86):
 > 1> <<1.0:64/float>>.
 > <<63,240,0,0,0,0,0,0>>
 > (Pretty much as expected for a little endian machine)
 > 
 > (Running under Linux on ARM):
 > 1> <<1.0:64/float>>.
 > <<0,0,0,0,63,240,0,0>>
 > (Looks a bit like little endian, only the quads are swapped)

I run erlang r8b on linux on a big-endian PowerPC embedded system
with floating point emulation:

 1> <<1.0:64/float>>.
 <<63,240,0,0,0,0,0,0>>

I know very little about floating point arithmetic. I don't know if
that's "correct" or not, I'm just giving you another data point. The
Erlang build system isn't really built for cross-compiling, I had to
do a fair bit of manual tweaking to get things to work. I assume
you've checked what happened during autoconf, e.g. that you have

  ac_cv_c_bigendian=${ac_cv_c_bigendian=yes}

 > This essentially means that any code compiled with floating point
 > constants in it will not run on the other machine. It might also mean
 > other issues as well, but this is where I first discovered the
 > problem.

If you provide an example which fails I'll try it.

 >  I'm thinking it maybe could be a problem with the FP emulator?

Are you using the in-kernel FP emulation or the gcc 'soft-float'? See
also:

  http://codepoet.org/lists/busybox/2003-June/008547.html

Matthias



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