Problem with 64 bit FP under ARM

Bjorn Gustavsson <>
Tue Aug 26 10:10:07 CEST 2003


Martin Sandiford <> writes:

> Hello all,
> 
> I have a problem with 64 bit floating point numbers on an embedded
> SA1110 based machine running under Linux.
> 
> A summary of the problem:
> 
> (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)

This is the expected result on ANY machine. The default endian
is big, so <<1.0:64/float>> is just shorthand for <<1.0:64/big-float>>.
To get the native ordering, you could use <<1.0:64/native-float>>.

> I'm not an ARM expert, so I can only assume that the correct
> representation for a double on ARM is with the quads swapped with
> respect to "normal" LE ordering.  Does anyone here know if this is the
> case?  I'm thinking it maybe could be a problem with the FP emulator?
> (There is no FPU on this board).
> 

I don't know anything about the ARM.

It would be interesting if you could post the result of:

<<1.0:64/native-float>>

That should show exactly how floating point numbers are stored
internally.


/Bjorn
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Björn Gustavsson            Ericsson Utvecklings AB
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