gh-129275: avoid temporary buffer in dec_as_long() by skirpichev · Pull Request #129630 · python/cpython

bedevere-app

According to the documentation: "If rdata is non-NULL, it MUST be allocated by one of libmpdec’s allocation functions and rlen MUST be correct. If necessary, the function will resize rdata. Resizing is slow and should not occur if rlen has been obtained by a call to mpd_sizeinbase."

So, possible resizing in mpd_qexport_u32/16() is for guarding against broken log10() implementations (log10 is used in the mpd_sizeinbase()).

Issue: Avoid temporary allocation in dec_as_long() #129275

Temporary memory allocation slowdown conversion for small integers (~2 digits):

Benchmark	ref	patch
int(Decimal(1<<7))	499 ns	495 ns: 1.01x faster
int(Decimal(1<<300))	2.16 us	2.06 us: 1.05x faster
Geometric mean	(ref)	1.02x faster

Benchmark hidden because not significant (2): int(Decimal(1<<38)), int(Decimal(1<<3000))

Details

# bench_Decimal-to-int.py

import pyperf
from decimal import Decimal

values = ['1<<7', '1<<38', '1<<300', '1<<3000']

runner = pyperf.Runner()
for v in values:
    d = Decimal(eval(v))
    bn = 'int(Decimal('+v+'))'
    runner.bench_func(bn, int, d)