Christian Heimes added the comment: Am 28.10.2013 16:59, schrieb Charles-François Natali: > Well, unaligned memory access is usually slower on all architectures :-) > Also, I think some ARM architectures don't support unaligned access, so > it's not really a thing of the past...
On modern computers it's either not slower or just a tiny bit slower. http://lemire.me/blog/archives/2012/05/31/data-alignment-for-speed-myth-or-reality/ Python's str and bytes datatype are always aligned properly. The majority of bytearray and memoryview instances are aligned, too. Unaligned memory access is rare case for most applications. About 50% of strings have less than 8 bytes (!), 90% have less than 16 bytes. For the Python's test suite the numbers are even smaller: ~45% <=5 bytes, ~90% <=12 bytes. You might see a 10% slowdown for very long and unaligned byte arrays on some older CPUs. I think we can safely ignore the special case. Any special case for unaligned memory will introduce additional overhead that *will* slow down the common path. Oh, and ARM has unaligned memory access: http://infocenter.arm.com/help/index.jsp?topic=/com.arm.doc.ddi0360f/CDFEJCBH.html ---------- _______________________________________ Python tracker <rep...@bugs.python.org> <http://bugs.python.org/issue19183> _______________________________________ _______________________________________________ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
