From 89446b2c91b664a851874b43a295859c8383343d Mon Sep 17 00:00:00 2001 From: Mark Dickinson Date: Sun, 21 Aug 2016 10:59:48 +0100 Subject: [PATCH] Issue #25604: Fix bug in integer true division that could have resulted in off-by-one-ulp results in unusual cases. --- Misc/NEWS | 4 ++++ Objects/longobject.c | 4 ++-- 2 files changed, 6 insertions(+), 2 deletions(-) diff --git a/Misc/NEWS b/Misc/NEWS index e393d322f90e..392e9e7f88a5 100644 --- a/Misc/NEWS +++ b/Misc/NEWS @@ -10,6 +10,10 @@ What's New in Python 2.7.13? 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 #27473: Fixed possible integer overflow in str, unicode and bytearray concatenations and repetitions. Based on patch by Xiang Zhang. diff --git a/Objects/longobject.c b/Objects/longobject.c index ead8f284b757..6f469bf3e32e 100644 --- a/Objects/longobject.c +++ b/Objects/longobject.c @@ -3315,9 +3315,9 @@ 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]; -- 2.47.3