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August 1993
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1993.08.18 19:11 "Re: byte swapping 16- and 32-bit data", by Sam Leffler
To: craigh@g2syd.genasys.com.au, tiff@sgi.sgi.com
Subject: Re: byte swapping 16- and 32-bit data
From: mccoy@pixar.com (Dan McCoy)
Date: Wed, 18 Aug 93 10:57:00 PDT
....
Sam A: you get correct data for files written on a similar machine
and byte-swapped data for files written on a machine of the
opposite byte-order. A routine is provided to check whether
or not you need to fix up the data.
Me B: you always get correct data no matter where the file was
written. The speed for files written on a similar machine
is the same as above. There is a minor performance hit for files
written on a machine of the opposite byte-order.
The performance issue is the crux of the matter. If a separate
pass is made of data just to do byte swapping, it will be noticed;
through not for small images.
I also suggested that if performance is enough of an issue, you could
add an option to toggle between approaches A and B.
Sam has strongly nixed the option. (Fine with me.)
It does sound like he is implementing approach B.
I've made mods to the library to do byte-swapping after data is
decoded. The mods were done in such a way that the compression
routines can override the default behaviour if they are changed
to roll the byte-swap work in with the decoding. I did not
provide a client interface to control this because I believe that
it's important for the library to maintain a consistent interface.
If the performance hit is too large, then I'll revisit this
decision in a later release.
Sam