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Fixed #30363 -- Do not use exponential notation for small decimal numbers. 

In 9cc6a60040b0f64f8ea066dd215176d4bd16621d a security patch was
introduced to prevent allocating large segments of memory when a
very large or very small decimal number was to be formatted.

As a side-effect, there was a change in formatting of small decimal
numbers even when the `decimal_pos` argument was provided, which meant
that reasonable small decimal numbers (above 1e-199) would be formatted
as `0.00`, while smaller decimal numbers (under 1e-200) would be
formatted as `1e-200`.
This commit is contained in:
Sjoerd Job Postmus 2019-04-13 12:11:34 +02:00 committed by Florian Apolloner
parent ba72606760
commit e6d57c4d65
2 changed files with 9 additions and 1 deletions
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8
django/utils/numberformat.py
View File

@ -27,6 +27,14 @@ def format(number, decimal_sep, decimal_pos=None, grouping=0, thousand_sep='',
# sign # sign
sign = '' sign = ''
if isinstance(number, Decimal): if isinstance(number, Decimal):
if decimal_pos is not None:
# If the provided number is too small to affect any of the visible
# decimal places, consider it equal to '0'.
cutoff = Decimal('0.' + '1'.rjust(decimal_pos, '0'))
if abs(number) < cutoff:
number = Decimal('0')
# Format values with more than 200 digits (an arbitrary cutoff) using # Format values with more than 200 digits (an arbitrary cutoff) using
# scientific notation to avoid high memory usage in {:f}'.format(). # scientific notation to avoid high memory usage in {:f}'.format().
_, digits, exponent = number.as_tuple() _, digits, exponent = number.as_tuple()

2
tests/utils_tests/test_numberformat.py
View File

@ -94,7 +94,7 @@ class TestNumberFormat(SimpleTestCase):
('1e-10', 8, '0.00000000'), ('1e-10', 8, '0.00000000'),
('1e-11', 8, '0.00000000'), ('1e-11', 8, '0.00000000'),
('1' + ('0' * 300), 3, '1.000e+300'), ('1' + ('0' * 300), 3, '1.000e+300'),
('0.{}1234'.format('0' * 299), 3, '1.234e-300'), ('0.{}1234'.format('0' * 299), 3, '0.000'),
] ]
for value, decimal_pos, expected_value in tests: for value, decimal_pos, expected_value in tests:
with self.subTest(value=value): with self.subTest(value=value):