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Tue May 9 12:44:00 GMT 2000

Jon> Note that the first word of a Java object shouldn't be
Jon> significant for GC, since it's always the vtable.
In some cases we need to mark a vtable because that is how we can mark
the Class object.
Jon> If the high-order bit is zero, the bitmask contains a bit pattern
Jon> of all pointers in the object; if the high-order bit is non-zero,
Jon> it contains a negative offset to a location containing a counted
Jon> bitmask.
This is the same idea as hiding a pointer here, just using a different
encoding.
It is worth looking into doing this. I don't know how much effect it
will really have. For all we know, for very large objects the
overhead of a mark function is negligable.
If somebody wants to look into this and see what impact it has, I'm
all ears...
Tom