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Fix signed subtraction overflow in CBigNum::setint64().

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As noticed by sipa (Pieter Wuille), this can happen when CBigNum::setint64() is
called with an integer value of INT64_MIN (-2^63).

When compiled with -ftrapv, the program would crash. Otherwise, it would
execute an undefined operation (although in practice, usually the correct one).
This commit is contained in:
Ricardo M. Correia 2012-05-14 21:17:24 +02:00
parent 62e0453ce0
commit 5849bd472a
1 changed files with 9 additions and 1 deletions
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10
src/bignum.h
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@ -131,7 +131,15 @@ public:
if (sn < (int64)0)
{
n = -sn;
// We negate in 2 steps to avoid signed subtraction overflow,
// i.e. -(-2^63), which is an undefined operation and causes SIGILL
// when compiled with -ftrapv.
//
// Note that uint64_t n = sn, when sn is an int64_t, is a
// well-defined operation and n will be equal to sn + 2^64 when sn
// is negative.
n = sn;
n = -n;
fNegative = true;
} else {
n = sn;