#13352: Running time improvement of the bitset_len method
---------------------------------+------------------------------------------
Reporter: dcoudert | Owner: jason
Type: enhancement | Status: needs_review
Priority: major | Milestone: sage-5.3
Component: misc | Resolution:
Keywords: | Work issues:
Report Upstream: N/A | Reviewers:
Authors: David Coudert | Merged in:
Dependencies: | Stopgaps:
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Description changed by dcoudert:
Old description:
> This patch improves the running time of the {{{bitset_len}}} method by
> using fast methods for counting bits in 32 and 64 bits integers
> (popcount). It
> - adds file {{{bitcount.pxi}}} to {{{sage/misc/}}}. This file contains
> the functions for counting bits in 32 or 64 bits integers
> - adds corresponding tests to file {{{misc_c.pyx}}}
> - modifies the {{{bitset_len}}} function accordingly
>
> Before:
> {{{
> sage: x = FrozenBitset('10'*1003002); len(x)
> 1003002
> sage: %timeit len(x)
> 125 loops, best of 3: 5.27 ms per loop
> sage: x = FrozenBitset('10'*10705); len(x)
> 10705
> sage: %timeit len(x)
> 625 loops, best of 3: 56.3 µs per loop
> }}}
>
> After:
> {{{
> sage: x = FrozenBitset('10'*1003002); len(x)
> 1003002
> sage: %timeit len(x)
> 625 loops, best of 3: 865 µs per loop
> sage: x = FrozenBitset('10'*10705); len(x)
> 10705
> sage: %timeit len(x)
> 625 loops, best of 3: 9.39 µs per loop
> }}}
>
> The ``popcount_32`` method is the same than the function used in patch
> #12371.
>
> The alternative would be to use functions {{{__builtin_popcount()}}} and
> {{{__builtin_popcountll()}}}. They are extremely fast but they required
> to add flag ``-mpopcnt`` or ``-msse4.2`` to the gcc compiler. Can we do
> that? how?
>
> APPLY:
>
> * trac_13352_bitset_len.patch
New description:
This patch improves the running time of the {{{bitset_len}}} method by
using fast methods for counting bits in 32 and 64 bits integers
(popcount). It
- adds file {{{bitcount.pxi}}} to {{{sage/misc/}}}. This file contains the
functions for counting bits in 32 or 64 bits integers
- adds corresponding tests to file {{{misc_c.pyx}}}
- modifies the {{{bitset_len}}} function accordingly
Before:
{{{
sage: x = FrozenBitset('10'*1003002); len(x)
1003002
sage: %timeit len(x)
125 loops, best of 3: 5.27 ms per loop
sage: x = FrozenBitset('10'*10705); len(x)
10705
sage: %timeit len(x)
625 loops, best of 3: 56.3 µs per loop
}}}
After:
{{{
sage: x = FrozenBitset('10'*1003002); len(x)
1003002
sage: %timeit len(x)
625 loops, best of 3: 865 µs per loop
sage: x = FrozenBitset('10'*10705); len(x)
10705
sage: %timeit len(x)
625 loops, best of 3: 9.39 µs per loop
}}}
The ``popcount_32`` method is the same than the function used in patch
#12371.
The alternative would be to use functions {{{__builtin_popcount()}}} and
{{{__builtin_popcountll()}}}. They are extremely fast but they required to
add flag ``-mpopcnt`` or ``-msse4.2`` to the gcc compiler. Can we do that?
how?
APPLY:
* [attachment:trac_13352_bitset_len.patch]
--
--
Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/13352#comment:4>
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