Re: immediate strings #2

[Dmitry Antipov]

On 11/29/2011 12:50 PM, Paul Eggert wrote:

> 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.

It looks like I miss the point. For an immediate strings, we need
two extra bits - 1 for GC, 1 for string subtype, so the question is
simple: where to get them if both size and size_byte are ptrdiff_t?

Dmitry