[Patches] [ python-Patches-717102 ] Fetch oparg with unsigned short
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Mon, 07 Apr 2003 18:32:21 -0700
Patches item #717102, was opened at 2003-04-07 19:16
Message generated for change (Comment added) made by tim_one
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Category: Core (C code)
Group: Python 2.3
Status: Open
Resolution: None
Priority: 5
Submitted By: Raymond Hettinger (rhettinger)
>Assigned to: Raymond Hettinger (rhettinger)
Summary: Fetch oparg with unsigned short
Initial Comment:
This is faster than retrieving two unsigned chars and
assembling them with a shift and bitwise-or.
Wrapped in a conditional macro because the
transformation only works for little endian
architectures.
Tim, is there something better than MS_WINDOWS to
test for a little endian environment?
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>Comment By: Tim Peters (tim_one)
Date: 2003-04-07 21:32
Message:
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You could write an autoconfig test to determine the
endianness of the box, and then builds for non-Unix
platforms would need to define the symbol (or not) by
hand. We do that for lots of stuff already. In fact, I'm
pretty sure autoconf already generates endian info.
I discourage using this, though. HW-related ifdefs are a
nightmare to maintain over time, and an optimizing
compiler should be smart enough to do this transformation
on its own -- provided it's really a win on the platform at
hand. The architecture trend is toward penalizing unaligned
access of all kinds, and if you didn't test this under every
flavor of Pentium that has been, and ever will be, released,
you don't know all its effects on speed. That's why HW-
related ifdefs become a nightmare over time.
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