[Mesa-dev] [PATCH v2 07/12] mesa: glGet: simplify the 'enum not found' condition

[Brian Paul]

On 09/10/2012 12:41 AM, Imre Deak wrote:
> When traversing the hash table looking up an enum that is invalid we
> eventually reach the first element in the descriptor array. By looking
> at the type of that element, which is always TYPE_API_MASK, we know that
> we can stop the search and return error. Since this element is always
> the first it's enough to check for its index being 0 without looking at
> its type.
>
> Later in this patchset, when we generate the hash tables during build
> time, this will allow us to remove the TYPE_API_MASK and related flags
> completly.
>
> Signed-off-by: Imre Deak<imre.deak at intel.com>
> ---
>   src/mesa/main/get.c |    8 +++++---
>   1 file changed, 5 insertions(+), 3 deletions(-)
>
> diff --git a/src/mesa/main/get.c b/src/mesa/main/get.c
> index 63fe296..48c6911 100644
> --- a/src/mesa/main/get.c
> +++ b/src/mesa/main/get.c
> @@ -2012,16 +2012,18 @@ find_value(const char *func, GLenum pname, void **p, union value *v)
>      mask = Elements(table(api)) - 1;
>      hash = (pname * prime_factor);
>      while (1) {
> -      d =&values[table(api)[hash&  mask]];
> +      int idx = table(api)[hash&  mask];
>
>         /* If the enum isn't valid, the hash walk ends with index 0,
> -       * which is the API mask entry at the beginning of values[]. */
> -      if (unlikely(d->type == TYPE_API_MASK)) {
> +       * pointing to the first entry of values[] which doesn't hold
> +       * any valid enum. */
> +      if (unlikely(!idx)) {

Minor nit, but I think "idx != 0" would be nicer here.


>            _mesa_error(ctx, GL_INVALID_ENUM, "%s(pname=%s)", func,
>                  _mesa_lookup_enum_by_nr(pname));
>            return&error_value;
>         }
>
> +      d =&values[idx];
>         if (likely(d->pname == pname))
>            break;
>

To be honest, I'm not quite sure I understand how this code works and 
how we wind up at entry[0] for an invalid enum.

Anyway,  Reviewed-by: Brian Paul <brianp at vmware.com>