[Top][All Lists]

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: struct displacements

From: Ludovic Courtès
Subject: Re: struct displacements
Date: Tue, 26 Jan 2010 00:10:27 +0100
User-agent: Gnus/5.13 (Gnus v5.13) Emacs/23.1 (gnu/linux)


Andy Wingo <address@hidden> writes:

> On Mon 25 Jan 2010 14:44, address@hidden (Ludovic Courtès) writes:
>> Andy Wingo <address@hidden> writes:
>>>     -  GC_REGISTER_DISPLACEMENT (2*sizeof(scm_t_bits)); /* for the self 
>>> data pointer */
>>>     -  GC_REGISTER_DISPLACEMENT (2*sizeof(scm_t_bits)
>>>     -                            + scm_tc3_struct); /* for the vtable data 
>>> pointer */
>>>     +  /* The first word of a struct is equal to `SCM_STRUCT_DATA (vtable) +
>>>     +     scm_tc3_struct', and `SCM_STRUCT_DATA (vtable)' is 2 words after 
>>> VTABLE by
>>>     +     default.  */
>>>     +  GC_REGISTER_DISPLACEMENT (2 * sizeof (scm_t_bits) + scm_tc3_struct);
>>> I'm pretty sure the first case is still needed, for instance
>>> reallocation. It is, as the comment indicates, "for the self data
>>> pointer" -- the second word of the object, which normally points to the
>>> third word of the object, but for reallocated instances points to the
>>> third word of *another* object.
>> As an excuse, the comment was a bit too terse for me to understand, but
>> I get your point now.  However, it’s still unclear to me how an ‘s’
>> field can point to something else than “self”.
> Hm, I think you're right; the wording was not only terse but misleading.
> It is "for the data pointer, which might point to another object's
> data", or something like that. Nothing to do with `s' fields.

OK, done:


reply via email to

[Prev in Thread] Current Thread [Next in Thread]