#13352: Running time improvement of the bitset_len method
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Reporter: dcoudert | Owner: jason
Type: enhancement | Status: needs_review
Priority: major | Milestone: sage-5.12
Component: misc | Resolution:
Keywords: | Merged in:
Authors: David Coudert | Reviewers:
Report Upstream: N/A | Work issues:
Branch: | Commit:
Dependencies: | Stopgaps:
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Comment (by ncohen):
HMmmmmmmmm.... I'm trying to understand the code and it's much more
complicated than what I actually read. Funny, looks like you can have as
much fun with GCC than with Python, and decide how stuff is to be run at
run time instead of compile time `:-P`
This being said, if I understand well what "ifunc" does I do not see how
the popcount instruction will be used when available. To me it looks like
you should make sure that the file is compiled with the `-mpopcnt` GCC
flag (so that `__builtin_popcnt` is always replaced by the popcount
instruction even if it does not exist), and that this ifunc trick means to
avoid using this instruction if it is detected that, at runtime, it is not
available.
This being said, it is a very nice trick `O_o`
Nathann
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Ticket URL: <http://trac.sagemath.org/ticket/13352#comment:11>
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