Re: C++ ptrmemfun break if FUNCTION_BOUNDARY < 2 * BITS_PER_UNIT

[Alexandre Oliva <aoliva@redhat.com>]

On Apr 18, 2001, Richard Earnshaw <rearnsha@arm.com> wrote:

> aoliva@redhat.com said:
>> I don't want to extract a bit.  I want to extract the remaining bits.
>> The delta was shifted left (or multiplied by 2) to make room for the
>> vbit; now I want the delta back.  It's a signed offset.  

> This is OK, provided that you can guarantee that the left shift won't 
> cause the "sign" bit to change value.

Since the delta is as wide as a pointer, in order for a left-shift to
modify its sign bit we'd need a single C++ object that takes more than
half the address space of a machine.  Actually, we need a C++ object
so complicated that one of its bases ends up with such a large offset.
I believe we can assume no such objects are never going to be defined.

-- 
Alexandre Oliva   Enjoy Guarana', see http://www.ic.unicamp.br/~oliva/
Red Hat GCC Developer                  aoliva@{cygnus.com, redhat.com}
CS PhD student at IC-Unicamp        oliva@{lsd.ic.unicamp.br, gnu.org}
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