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gh-140036: _pydecimal: avoid slow exponentiation in floor division #140044

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gh-140036: _pydecimal: avoid slow exponentiation in floor division #140044

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ee617bd
_pydecimal: avoid slow exponentiation in floor division
picnixz Oct 13, 2025
329c31a
refine `q < 10**context.prec` checks
picnixz Oct 14, 2025
103fe1e
_pydecimal: add helpers for computing len(str(q)) < a
picnixz Oct 26, 2025
efbdc0a
_pydecimal: use helpers for computing len(str(q)) < a
picnixz Oct 26, 2025
9377ab6
_pydecimal: add tests for unbounded contexts
picnixz Oct 26, 2025
23494fb
Apply suggestions from code review
picnixz Nov 7, 2025
6b55711
address review
picnixz Nov 9, 2025
49d5b0d
reformulate comment
picnixz Nov 9, 2025
ea3e499
Update Lib/_pydecimal.py
picnixz Nov 9, 2025
b1c24b7
add test for _is_less_than_pow10a_use_str() slow path
picnixz Nov 9, 2025
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_pydecimal: add tests for unbounded contexts
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@picnixz
picnixz committed Oct 26, 2025
commit 9377ab6240bcc07e97ee122b1a35370a25cc1709
26 changes: 26 additions & 0 deletions Lib/test/test_decimal.py
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Original file line number Diff line number Diff line change
Expand Up @@ -24,6 +24,7 @@
with the corresponding argument.
"""

import contextlib
import logging
import math
import os, sys
Expand Down Expand Up @@ -4493,6 +4494,15 @@ def test_decimal_attributes(self):

class Coverage:

@contextlib.contextmanager
def unbound_context(self, prec=None, Emax=None, Emin=None):
with self.decimal.localcontext() as c:
c.prec = self.decimal.MAX_PREC if prec is None else prec
c.Emax = self.decimal.MAX_EMAX if Emax is None else Emax
c.Emin = self.decimal.MIN_EMIN if Emin is None else Emin
c.traps[self.decimal.Inexact] = 1
yield c

def test_adjusted(self):
Decimal = self.decimal.Decimal

Expand Down Expand Up @@ -4660,6 +4670,22 @@ def test_divmod(self):
self.assertTrue(c.flags[InvalidOperation] and
c.flags[DivisionByZero])

def test_divide_unbound_context(self):
with self.unbound_context() as c:
x = self.decimal.Decimal('1')
y = x // 1 # should be fast

def test_remainder_near(self):
L = 1000
limit = sys.get_int_max_str_digits()
sys.set_int_max_str_digits(L)
self.addCleanup(sys.set_int_max_str_digits, limit)

with self.unbound_context(prec=2 * L) as c:
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self.assertEqual(c.prec, 2 * L)
x = self.decimal.Decimal(f'1e{L}')
y = x.remainder_near(1) # must not raise a ValueError

def test_power(self):
Decimal = self.decimal.Decimal
localcontext = self.decimal.localcontext
Expand Down
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