[issue29782] Use __builtin_clzl for bits_in_digit if available

[Niklas Fiekas]

New submission from Niklas Fiekas:

Baseline performance (9e6ac83acae):
    
$ ./python -m timeit "12345678 == 12345678.0"
5000000 loops, best of 5: 40 nsec per loop
$ ./python -m timeit "1 == 1.0"
10000000 loops, best of 5: 38.8 nsec per loop
$ ./python -m timeit "(1234578987654321).bit_length()"
10000000 loops, best of 5: 39.4 nsec per loop

Upcoming PR:

$ ./python -m timeit "12345678 == 12345678.0"
10000000 loops, best of 5: 34.3 nsec per loop
$ ./python -m timeit "1 == 1.0"
10000000 loops, best of 5: 34.4 nsec per loop
$ ./python -m timeit "(1234578987654321).bit_length()"
10000000 loops, best of 5: 36.4 nsec per loop

----------
components: Interpreter Core
messages: 289353
nosy: niklasf
priority: normal
severity: normal
status: open
title: Use __builtin_clzl for bits_in_digit if available
type: performance
versions: Python 3.7

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Python tracker <report at bugs.python.org>
<http://bugs.python.org/issue29782>
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