Re: [Modulos-devel] Gotos?

[Luiz H. S. <shi...@in...>]

On Fri, 18 Jan 2002, Stephen Caldwell wrote:
> Do you think it's wise to use gotos so much? 99.99% C/C++ of the programming community would say that gotos are bad. 

You're right. But I use gotos to generate better code.

Usually I use gotos when an error occurs and something must be done to
undo what was done.

Like this:

    if (MemManager_AllocObj(mapCache, (void**)&map))
        return NULL;
    TaskManager_P(&task->mapSem);
    /* get address if not FIXED */
    if (!(prop & UserModManager_FIXED_ADDR)) {
        start = GetUnmappedArea(task, start, len, align);
        if (!start)
            goto errorFreeMap;
    } else {
        /* free old mappings */
        if (DestroyMapping(task, start, len)) {
            start = NULL;
errorFreeMap:
            MemManager_FreeObj(mapCache, map);
            goto errorV;
        }
    }
    ...
    ...
errorV:
    TaskManager_V(&task->mapSem, 0);
    return start;
}

Without gotos:

    if (MemManager_AllocObj(mapCache, (void**)&map))
        return NULL;
    TaskManager_P(&task->mapSem);
    /* get address if not FIXED */
    if (!(prop & UserModManager_FIXED_ADDR)) {
        start = GetUnmappedArea(task, start, len, align);
        if (!start) {
            MemManager_FreeObj(mapCache, map);
            TaskManager_V(&task->mapSem, 0);
            return NULL;
        }
    } else {
        /* free old mappings */
        if (DestroyMapping(task, start, len)) {
            MemManager_FreeObj(mapCache, map);
            TaskManager_V(&task->mapSem, 0);
            return NULL;
        }
    }
    ...
    ...
    TaskManager_V(&task->mapSem, 0);
    return start;
}

You can see a lot of duplicate code. But the compiler can't! So I have to
use gotos to generate smaller code.

That's a common practice. Look Linux, FreeBSD, etc, etc.

If you see some code that can be changed to eliminate a goto without
making the code bigger. Please, tell me. I'll be glad to change it.

See you,

Luiz Henrique Shigunov (shi...@in...)    ICQ: 103562572
Visit ModulOS: http://modulos.sourceforge.net/
Personal Page: http://www.inf.ufsc.br/~shigunov/