[Python-Dev] cpython (2.7): Fix comment blocks. Adjust blocksize to a power-of-two for better divmod (original) (raw)
Guido van Rossum guido at python.org
Tue Jun 25 06:10:18 CEST 2013
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On Mon, Jun 24, 2013 at 7:47 PM, Raymond Hettinger < raymond.hettinger at gmail.com> wrote:
On Jun 24, 2013, at 4:07 AM, Victor Stinner <victor.stinner at gmail.com> wrote: Out of curiosity, do you know (remember) how was the number 62 chosen? Is it a compromise between memory usage and performances? 62 is surprising because it is not a power of two :-) Is it to just have 64 (2+62) pointers in the structure? Yes, the goal was to have the struct size be an exact multiple of the cache line length (always a power-of-two, typically 64 bytes). What was different then is that deques weren't indexable. When indexing was added, the size of 62 became an unfavorable choice because it made the division and modulo calculation in dequeindex() slower than for a power of two.
A-ha! Finally an explanation of the change. It makes intuitive sense now. I think the general feeling is that folks overreacted (perhaps confused by your silence) and that the reversal will be rolled back. Benjamin?
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