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Issue #25604: Fix minor bug in integer true division, which could 

have caused off-by-one-ulp results on certain platforms.
This commit is contained in:
Mark Dickinson 2016-08-21 10:23:23 +01:00
parent 164a3c822d
commit dc590a4cc3
2 changed files with 6 additions and 2 deletions
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4
Misc/NEWS
View File

@ -10,6 +10,10 @@ What's New in Python 3.6.0 beta 1
Core and Builtins
-----------------
- Issue #25604: Fix a minor bug in integer true division; this bug could
potentially have caused off-by-one-ulp results on platforms with
unreliable ldexp implementations.
- Issue #27662: Fix an overflow check in ``List_New``: the original code was
checking against ``Py_SIZE_MAX`` instead of the correct upper bound of
``Py_SSIZE_T_MAX``. Patch by Xiang Zhang.

4
Objects/longobject.c
View File

@ -3893,9 +3893,9 @@ long_true_divide(PyObject *v, PyObject *w)
/* Round by directly modifying the low digit of x. */
mask = (digit)1 << (extra_bits - 1);
low = x->ob_digit[0] | inexact;
if (low & mask && low & (3*mask-1))
if ((low & mask) && (low & (3U*mask-1U)))
low += mask;
x->ob_digit[0] = low & ~(mask-1U);
x->ob_digit[0] = low & ~(2U*mask-1U);
/* Convert x to a double dx; the conversion is exact. */
dx = x->ob_digit[--x_size];