[Webkit-unassigned] [Bug 70691] BitVector isInline check could fail

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=70691


Geoffrey Garen <ggaren at apple.com> changed:

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                 CC|                            |ggaren at apple.com




--- Comment #2 from Geoffrey Garen <ggaren at apple.com>  2011-10-23 11:33:08 PST ---
> One possible fix is to use the lowest bit of m_bitsOrPointer to indicate inline or outofline, based on the assumption that the pointer to OutOfLineBits should be 4 or 8 byte aligned (please correct me if we can safely make this assumption).

I think this is a reasonable assumption.

You can do two things to make your assumption clearer to the reader:

(1) Add an ASSERT(!isInline()) at the end of BitVector::resizeOutOfLine()

(2) Add a comment above the declaration of m_bitsOrPointer explaining what the low bit means:

"The low bit of m_bitsOrPointer is a flag indicating whether this field is inline bits or a pointer to out of line bits. If the flag is set, the field is inline bits. This works because the low bit in a pointer is always unset."

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