shift-divmod 0.0.2

Implement faster divmod() for moduli with trailing 0 bits

Info:

This is the README file for ShiftDivMod.

Author:

Shlomi Fish <[e-mail]>

Copyright:

© 2020, Shlomi Fish.

Date:

2020-09-13

Version:

0.0.2

PURPOSE

This distribution implements faster divmod() (and .mod()) operations for moduli with a large number of trailing 0 bits (where the div/mod base is divisible by 2 ** n for an integer n).

It should yield the same result as the built-n divmod() function for positive numerators (its behaviour for negative ones is currently untested and undefined).

INSTALLATION

pip3 install shift_divmod

USAGE

from shift_divmod import ShiftDivMod

base = 997
shift = 1200
modder = ShiftDivMod(base, shift)
# Alternative constructor which may require more
# work and eventualy calls the default constructor
modder = ShiftDivMod.from_int(base << shift)

x = 10 ** 500
# Same as divmod(x, (base << shift))
print( modder.divmod(x) )

NOTES

The code from which this distribution has been derived, was proposed as a proof-of-concept for a potential improvement for the built in cpython3 operations here: https://bugs.python.org/issue41487 . However, changing cpython3 in this manner was rejected.

libdivide ( https://github.com/ridiculousfish/libdivide ) provides a different, but also interesting, approach for optimizing division.

COPYRIGHT

Copyright © 2020, Shlomi Fish. All rights reserved.

Redistribution and use in source and binary forms, with or without modification, are permitted provided that the following conditions are met:

1. Redistributions of source code must retain the above copyright notice, this list of conditions, and the following disclaimer.

2. Redistributions in binary form must reproduce the above copyright notice, this list of conditions, and the following disclaimer in the documentation and/or other materials provided with the distribution.

3. Neither the name of the author of this software nor the names of contributors to this software may be used to endorse or promote products derived from this software without specific prior written consent.

THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS “AS IS” AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.