Hi Nigel,
The number is the result of further manipulation. I think the
manipulation may be the problem here.
I have tried the code on IDL 6.3 64 bit and IDL 6.1 32 bit in linux
[both little endian machines] - both with the same problem!
Code extract follows. The final values are stored in the 'a' matrix. I
dont have the documentation for the binary file format handy.
openr,u,fnm, /get_lun
status = FSTAT(u)
dd = status.size / (4*60)
a=lonarr(dd,60)
bdat=byte(1)
dat=bytarr(4)
for j=0,dd-1 do $ ;Loop to count total data rows and
begin
for i=0,59 do $
begin
fdat=double(0.0)
sgn=1.
for aa=0,3 do $ ;data component rows in file.
begin
READU,u,bdat
dat(aa)=bdat
end
dat(0)=dat(0)-64 ; take off 2^30
fdat=dat(0)*256.*256.*256.+dat(1)*256.*256.+dat(2)*256.+dat( 3)
fdat=sgn*fdat
a[j,i]=fdat
end
endfor
free_lun, u
Any ideas? I assume Linux must handle some part of the above
differently.
Thanks.
Russell.
On Jan 9, 9:06 pm, Nigel Wade <n...@ion.le.ac.uk> wrote:
> RussellGrew wrote:
>> Hello,
>
>> Interesting scenario here. I have some code (not written by myself)
>> that reads a bunch of data series from a binary file.
>
>> Most of the data series contain positive floating point numbers. One
>> of them contains negative numbers. On windows, this works fine. On
>> linux, whenever the negative numbers should appear, the values have
>> reverted to -2147.48. The series with only positive numbers reads fine
>> on both machines.
>
> That looks very suspicious. It's 32bit -MAXINT, with a decimal scaling factor.
>
>
>
>> There is some manipulation to produce the data series.
>
> Is the number above what is read by IDL, or the result of the "manipulation"?
>
>
>
>> Both machines are little endian, checked with
>
> http://www.dfanning.com/tips/endian_machines.html,
>
>> using IDL6.3 in both cases. Linux is 64bit gentoo, windows is a 64bit
>> processor running 32 bit windows.
>
>> Ideas? Perhaps there is some obvious difference between platforms that
>> I am unaware of?
>
> There shouldn't be. What method are you using to read the floating point binary
> data? Are you running a 32bit or 64bit version of IDL on Linux, and are the
> floating point numbers 32bit or 64bit (float or double)? READU should work the
> same on all platforms provided the data is in the correct machine format and
> you ask it to read floats/doubles.
>
> For example, this writes a 32bit and 64bit floating point values to a file, then
> reads them back. The platform is 64bit Linux and IDL is 64bit.
>
> IDL Version 6.4 (linux x86_64 m64). (c) 2007, ITT Visual Information Solutions
> IDL> a=float(-32.0)
> IDL> b=double(-64)
> IDL> openw,1,'tmp.tmp'
> IDL> writeu,1,a,b
> IDL> close,1
> IDL> openr,2,'tmp.tmp'
> IDL> c=float(1)
> IDL> d=double(1)
> IDL> readu,2,c,d
> IDL> print,c,d
> -32.0000 -64.000000
> IDL> exit
>
> I can also read it back using 32bit IDL:
>
> IDL Version 6.4 (linux x86 m32). (c) 2007, ITT Visual Information Solutions
> IDL> c=float(1)
> IDL> d=double(1)
> IDL> openr,2,'tmp.tmp'
> IDL> readu,2,c,d
> IDL> print,c,d
> -32.0000 -64.000000
>
> If I transfer the binary file tmp.tmp to a 32bit Windows machine I can still
> read it using the same code.
>
> --
> Nigel Wade, System Administrator, Space Plasma Physics Group,
> University of Leicester, Leicester, LE1 7RH, UK
> E-mail : n...@ion.le.ac.uk
> Phone : +44 (0)116 2523548, Fax : +44 (0)116 2523555
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