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Bug 1202556 - Detect underflow in TimeStamp addition/subtraction operators; r=froydnj

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This commit is contained in:
Brian Birtles 2015-09-14 09:47:09 +09:00
parent b71f4ee5fd
commit 557a21eb5d
1 changed files with 16 additions and 2 deletions
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18
mozglue/misc/TimeStamp.h
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@ -504,13 +504,27 @@ public:
TimeStamp& operator+=(const TimeDuration& aOther)
{
MOZ_ASSERT(!IsNull(), "Cannot compute with a null value");
mValue += aOther.mValue;
TimeStampValue value = mValue + aOther.mValue;
// Check for underflow.
// (We don't check for overflow because it's not obvious what the error
// behavior should be in that case.)
if (aOther.mValue < 0 && value > mValue) {
value = 0;
}
mValue = value;
return *this;
}
TimeStamp& operator-=(const TimeDuration& aOther)
{
MOZ_ASSERT(!IsNull(), "Cannot compute with a null value");
mValue -= aOther.mValue;
TimeStampValue value = mValue - aOther.mValue;
// Check for underflow.
// (We don't check for overflow because it's not obvious what the error
// behavior should be in that case.)
if (aOther.mValue > 0 && value > mValue) {
value = 0;
}
mValue = value;
return *this;
}