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Next: Application Launch failure
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External
Since: Sep 26, 2003
Posts: 61
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(Msg. 1) Posted: Fri Oct 13, 2006 1:55 pm
Post subject: byte swapping for floats on Intel Mac
Archived from groups: comp>sys>mac>programmer>misc (more info?)
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Hi,
we've got data in Little-endian format, which we need to convert to the
local Host format. I can't seem to find a way to do that. We've got
existing software which writes data out in Little-endian format, which may
be read on a Mac or on a PC, and now on an Intel Mac, so we need to have
code on the Mac side which will do the conversion properly in a Universal
Binary app, regardless of whether it's run on a PPC or an Intel Mac.
Here's the code I have now, but I don't think it's doing anything. I
think this just converts it from Host format right back to Host format, and
I need to convert it from Little-endian to Host format.
CFSwappedFloat32 swappedFloat = CFConvertFloatHostToSwapped(
theFloatToConvert );
return CFConvertFloatSwappedToHost( swappedFloat );
Anyone know how to do this properly?
Thanks,
-Howard |
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External
Since: Aug 04, 2003
Posts: 588
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(Msg. 2) Posted: Fri Oct 13, 2006 5:18 pm
Post subject: Re: byte swapping for floats on Intel Mac [Login to view extended thread Info.]
Archived from groups: per prev. post (more info?)
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In article ,
Howard wrote:
>Hi,
>
> we've got data in Little-endian format, which we need to convert to the
>local Host format. I can't seem to find a way to do that. We've got
>existing software which writes data out in Little-endian format, which may
>be read on a Mac or on a PC, and now on an Intel Mac, so we need to have
>code on the Mac side which will do the conversion properly in a Universal
>Binary app, regardless of whether it's run on a PPC or an Intel Mac.
>
> Here's the code I have now, but I don't think it's doing anything. I
>think this just converts it from Host format right back to Host format, and
>I need to convert it from Little-endian to Host format.
>
> CFSwappedFloat32 swappedFloat = CFConvertFloatHostToSwapped(
>theFloatToConvert );
> return CFConvertFloatSwappedToHost( swappedFloat );
>
> Anyone know how to do this properly?
Apple didn't provide the functions you need directly. So instead read
the float into a uint32, call CFSwapInt32LittleToHost on the result,
and convert that to float.
--
There's no such thing as a free lunch, but certain accounting practices can
result in a fully-depreciated one. |
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External
Since: Jan 12, 2005
Posts: 11
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(Msg. 3) Posted: Sun Oct 15, 2006 1:59 pm
Post subject: Re: byte swapping for floats on Intel Mac [Login to view extended thread Info.]
Archived from groups: per prev. post (more info?)
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Matthew Russotto wrote:
> In article ,
> Howard wrote:
> >Hi,
> >
> > we've got data in Little-endian format, which we need to convert to the
> >local Host format. I can't seem to find a way to do that. We've got
> >existing software which writes data out in Little-endian format, which may
> >be read on a Mac or on a PC, and now on an Intel Mac, so we need to have
> >code on the Mac side which will do the conversion properly in a Universal
> >Binary app, regardless of whether it's run on a PPC or an Intel Mac.
> >
> > Here's the code I have now, but I don't think it's doing anything. I
> >think this just converts it from Host format right back to Host format, and
> >I need to convert it from Little-endian to Host format.
> >
> > CFSwappedFloat32 swappedFloat = CFConvertFloatHostToSwapped(
> >theFloatToConvert );
> > return CFConvertFloatSwappedToHost( swappedFloat );
> >
> > Anyone know how to do this properly?
>
> Apple didn't provide the functions you need directly. So instead read
> the float into a uint32, call CFSwapInt32LittleToHost on the result,
> and convert that to float.
You have to be a bit careful when doing this. For example:
float myFloat = (float)CFSwapInt32LittleToHost((uint32_t)floatToSwap);
Well do the wrong thing. The type casts will *convert* the values to
floats and ints and since they have different bit patterns you will get
the wrong answer. The "correct" method is shown below which will
overlay a uint32 over the float's data bits rather then converting the
float value to an int (and vis versa).
uint32_t temp = CFSwapInt32LittleToHost(*((uint32_t*)&floatToSwap));
float myFloat = *((float*)&temp);
Michael >> Stay informed about: byte swapping for floats on Intel Mac |
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External
Since: Jan 05, 2004
Posts: 474
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(Msg. 4) Posted: Mon Oct 23, 2006 11:47 pm
Post subject: Re: byte swapping for floats on Intel Mac [Login to view extended thread Info.]
Archived from groups: per prev. post (more info?)
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In article ,
"Howard" wrote:
> Hi,
>
> we've got data in Little-endian format, which we need to convert to the
> local Host format. I can't seem to find a way to do that. We've got
> existing software which writes data out in Little-endian format, which may
> be read on a Mac or on a PC, and now on an Intel Mac, so we need to have
> code on the Mac side which will do the conversion properly in a Universal
> Binary app, regardless of whether it's run on a PPC or an Intel Mac.
Check out this long but useful thread:
<http://lists.apple.com/archives/carbon-dev/2006/Jul/msg00152.html> >> Stay informed about: byte swapping for floats on Intel Mac |
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External
Since: May 08, 2007
Posts: 8
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(Msg. 5) Posted: Fri Jan 12, 2007 1:00 pm
Post subject: Re: byte swapping for floats on Intel Mac [Login to view extended thread Info.]
Archived from groups: per prev. post (more info?)
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"Howard" wrote in message
> Hi,
>
> we've got data in Little-endian format, which we need to convert to
the
> local Host format. I can't seem to find a way to do that. We've got
> existing software which writes data out in Little-endian format, which may
> be read on a Mac or on a PC, and now on an Intel Mac, so we need to have
> code on the Mac side which will do the conversion properly in a Universal
> Binary app, regardless of whether it's run on a PPC or an Intel Mac.
>
> Here's the code I have now, but I don't think it's doing anything. I
> think this just converts it from Host format right back to Host format,
and
> I need to convert it from Little-endian to Host format.
>
> CFSwappedFloat32 swappedFloat = CFConvertFloatHostToSwapped(
> theFloatToConvert );
> return CFConvertFloatSwappedToHost( swappedFloat );
>
> Anyone know how to do this properly?
>
> Thanks,
> -Howard
I'm new to Macs but reading the docs, I thought that running PowerPC code on
Intel
chips was not a problem..
http://developer.apple.com/documentation/MacOSX/Conceptual/universal_b...ry/univ
"Rosetta is a translation process that runs a PowerPC binary on an
Intel-based Macintosh computer-it allows applications to run as nonnative
binaries." >> Stay informed about: byte swapping for floats on Intel Mac |
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External
Since: Oct 03, 2004
Posts: 2243
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(Msg. 6) Posted: Fri Jan 12, 2007 5:58 pm
Post subject: Re: byte swapping for floats on Intel Mac [Login to view extended thread Info.]
Archived from groups: per prev. post (more info?)
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In article ,
"Howard" wrote:
> Hi,
>
> we've got data in Little-endian format, which we need to convert to the
> local Host format. I can't seem to find a way to do that. We've got
> existing software which writes data out in Little-endian format, which may
> be read on a Mac or on a PC, and now on an Intel Mac, so we need to have
> code on the Mac side which will do the conversion properly in a Universal
> Binary app, regardless of whether it's run on a PPC or an Intel Mac.
>
> Here's the code I have now, but I don't think it's doing anything. I
> think this just converts it from Host format right back to Host format, and
> I need to convert it from Little-endian to Host format.
>
> CFSwappedFloat32 swappedFloat = CFConvertFloatHostToSwapped(
> theFloatToConvert );
> return CFConvertFloatSwappedToHost( swappedFloat );
>
> Anyone know how to do this properly?
>
> Thanks,
> -Howard
I would suggest that the way to do it _properly_ is to make it so that
the stored format is big-endian and use the functions/macros available
on all your target platforms (and just about every other one in use
today) that translate from big-endian to native.
The expedient way - which may not be very expedient depending on how
centralized your IO is - is to #ifdef up the Mac code based on which
architecture you're building for so it doesn't bother trying to swap on
x86.
--
The best intentions in the world don't make a flawed argument magically valid. >> Stay informed about: byte swapping for floats on Intel Mac |
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