r42961: bufstart != strstart

[Michael Hind]

I would agree you are correct.

If for some reason the encoding was changed, this could cause a problem, and
there are probably other areas where this could occur.  As they are
distinct, they should be treated as such.  I am not sure why darbelo changed
this.  I will check with him before either getting him to change this or
fixing it myself.

Cheers,

Michael (mikehh)


2009/12/10 Andy Dougherty <doughera at lafayette.edu>

> On Thu, 10 Dec 2009, Michael Hind wrote:
>
> > I don't know if this is relevant but it is defined in pobj.h as:
>
> Here is the relevant structure (where the first 3 elements are deliberately
> the same as in the Buffer structure):
>
>    struct parrot_string_t {
>         Parrot_UInt flags;
>        void *     _bufstart;
>        size_t     _buflen;
>         char       *strstart;
>        UINTVAL     bufused;
>        UINTVAL     strlen;
>        UINTVAL     hashval; /* cached hash value computation */
>
>        /*    parrot_string_representation_t representation;*/
>        const struct _encoding *encoding;
>        const struct _charset  *charset;
>    };
>
> My point is that I don't think it's guaranteed that _bufstart == strstart.
> They are equal when the string is initially created, but not guaranteed
> to stay that way.  For example, in src/string/api.c, in the function
> Parrot_str_substr(), there is this excerpt:
>
>        /* do in-place i.e. reuse existing header if one */
>        if (replace_dest && d && *d) {
>            PARROT_ASSERT(src->encoding == Parrot_fixed_8_encoding_ptr);
>            dest           = *d;
>
>            dest->encoding = src->encoding;
>            dest->charset  = src->charset;
>
>            dest->strstart = (char *)src->strstart + true_offset;
>            dest->bufused  = true_length;
>
>            dest->strlen   = true_length;
>            dest->hashval  = 0;
>        }
>
> where strstart is moved, but bufstart isn't.
>
> Hence my concern that this patch is wrong in simply replacing strstart by
> bufstart.
>
> --
>     Andy Dougherty              doughera at lafayette.edu
>



-- 
Michael H. Hind

Tel:  +44 (0) 1224 443 570
Cell: +44 (0) 7877 224 745
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