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Re: immediate strings #2

From: Paul Eggert
Subject: Re: immediate strings #2
Date: Tue, 29 Nov 2011 00:50:17 -0800
User-agent: Mozilla/5.0 (X11; Linux i686; rv:8.0) Gecko/20111124 Thunderbird/8.0

On 11/28/11 18:07, Stefan Monnier wrote:
> There are bits available in size and size_byte, we
> have to use those (like we currently do with gcmarkbit in `size')

There is a bit available in size (since it's always nonnegative)
but not in size_byte (since it ranges from -1 .. PTRDIFF_MAX
and is a ptrdiff_t, assuming a 32-bit host configured --with-wide-int
and assuming the memory-saving patch of Bug#9874).

This is in contrast with our current uses of mark bits (e.g.,
ARRAY_MARK_FLAG), which use bits that are otherwise unused, even if
a vector has its maximal size.

We can fairly easily get that bit back from size_byte by restricting
its range to (say) 0 .. PTRDIFF_MAX.

So this is a fairly minor glitch that can be fixed but is not yet
fixed in the current proposal.

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