On 29/08/2013 20:26, Hadley Wickham wrote:
Do pointers always have to be aligned?
Depends on the architecture, e.g., Sparc doesn't allow non-aligned pointers at
all (results in a segfault), SV x86_64 ABI specifies pointers to be aligned at
8 bytes, but the x86_64 CPUs will allow misaligned pointers with a performance
penalty (the same was true for x86 - i.e. misaligned pointers are tolerated
with a penalty).
Ok, so you might not have to align pointers a particular architecture,
but if you're writing code that you want to work across multiple
architectures you must.
Yes, and note too that you may or may not need to align doubles,
independently of pointers (and it may even be a compiler setting: it is
on Solaris).
Hadley
--
Brian D. Ripley, rip...@stats.ox.ac.uk
Professor of Applied Statistics, http://www.stats.ox.ac.uk/~ripley/
University of Oxford, Tel: +44 1865 272861 (self)
1 South Parks Road, +44 1865 272866 (PA)
Oxford OX1 3TG, UK Fax: +44 1865 272595
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