| Re: Possible Mac OS Bug with FIX. [message #44017] |
Wed, 11 May 2005 15:50  |
Dick Jackson
Messages: 347
Registered: August 1998
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Senior Member |
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<savoie@nsidc.org> wrote in message
news:ywkufywtwmdq.fsf@snowblower.colorado.edu...
> David Fanning <davidf@dfanning.com> writes:
>
>
>
>> What I am still not clear about, however, is whether whatever
>> the hell it is that RSI is doing is done *consistently*
>> across all machine architectures. Anyone have a theory about
>> that? :-)
>
> It seems pretty clear to me what's happening is what lajos previously
> stated. But the more I tried to articulate that, the less sense it made.
> Anyway, on my two machines,
>
>
> Linux little endian:
> ------------------
>
> IDL> tmp = bytarr(20)
> tmp = bytarr(20)
> IDL> tmp[15] = 5
> tmp[15] = 5
> IDL> print, fix(tmp[15]), fix(tmp,15)
> print, fix(tmp[15]), fix(tmp,15)
> 5 5
>
> On a Big Endian IRIX64 machine
> ----------------------------
> IDL> tmp=bytarr(20)
> IDL> tmp[15] = 5
> IDL> print, fix(tmp[15]), fix(tmp,15)
> 5 1280
>
>
> I don't even know if this helps.
I think you are exactly right, but to get David's consistency across
platforms:
IDL> tmp = bytarr(20)
IDL> tmp[15] = 5
IDL> result=fix(tmp,15)
IDL> print,result ; This should vary across platforms
5
IDL> swap_endian_inplace, result, /swap_if_little_endian
IDL> print,result ; This should be consistent across platforms
1280
(the reader will guess I'm on an Intel box, someone please test this
elsewhere!)
Now, there are still two issues that are for David to decide:
- do you really want /swap_if_little_endian or /swap_if_big_endian?
(either will give a consistent result)
- do you really want the bytes starting at an offset that is not a
multiple of the size of the type you're casting it to (Fix: 2 bytes)?
Hope this helps!
Cheers,
--
-Dick
Dick Jackson / dick@d-jackson.com
D-Jackson Software Consulting / http://www.d-jackson.com
Calgary, Alberta, Canada / +1-403-242-7398 / Fax: 241-7392
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