[Python-Dev] More compact dictionaries with faster iteration (original) (raw)
Antoine Pitrou solipsis at pitrou.net
Tue Dec 11 10:13:31 CET 2012
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Le Mon, 10 Dec 2012 18:17:57 -0500, Raymond Hettinger <raymond.hettinger at gmail.com> a écrit :
On Dec 10, 2012, at 2:48 AM, Christian Heimes <christian at python.org> wrote: > On the other hand every lookup and collision checks needs an > additional multiplication, addition and pointer dereferencing: > > entry = entriesbaseaddr + sizeof(PyDictKeyEntry) * idx
Currently, the dict implementation allows alternative lookup functions based on whether the keys are all strings. The choice of lookup function is stored in a function pointer. That lets each lookup use the currently active lookup function without having to make any computations or branches.
An indirect function call is technically a branch, as seen from the CPU (and not necessarily a very predictable one, although recent Intel CPUs are said to be quite good at that).
Regards
Antoine.
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