[issue1869] Builtin round function is sometimes inaccurate for floats

[George Boutsioukis]

George Boutsioukis <gboutsioukis at gmail.com> added the comment:

The issue is that the implementation of round includes multiplying the
number by 10**ndigits, thus unnecessarily losing some precision for
large numbers within the IEEE754 double limits. This means that even
smaller numbers can produce these results for higher ndigit values, eg.

>>> round(56294995342131.5, 3) #one less digit
56294995342131.508

In the submitted patch I used modf to split the number and keep the
integral intact.

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keywords: +patch
nosy: +gboutsioukis
Added file: http://bugs.python.org/file10944/round_patch.diff

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<http://bugs.python.org/issue1869>
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