[Mesa-dev] [PATCH 05/10] nir: Use well-known power-of-two test instead of util_bitscan

[Matt Turner]

On Fri, Nov 10, 2017 at 4:02 PM, Ian Romanick <idr at freedesktop.org> wrote:
> On 11/10/2017 04:54 PM, Matt Turner wrote:
>> On Fri, Nov 10, 2017 at 2:32 PM, Ian Romanick <idr at freedesktop.org> wrote:
>>> From: Ian Romanick <ian.d.romanick at intel.com>
>>>
>>> This prevents the next change from breaking the build, and I felt that
>>> it was different enough from the rest of that patch to stand on its own.
>>>
>>> Signed-off-by: Ian Romanick <ian.d.romanick at intel.com>
>>> ---
>>>  src/compiler/nir/nir_validate.c | 5 +++--
>>>  1 file changed, 3 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/src/compiler/nir/nir_validate.c b/src/compiler/nir/nir_validate.c
>>> index 9bf8c70..ca191d2 100644
>>> --- a/src/compiler/nir/nir_validate.c
>>> +++ b/src/compiler/nir/nir_validate.c
>>> @@ -979,8 +979,9 @@ validate_var_decl(nir_variable *var, bool is_global, validate_state *state)
>>>
>>>     validate_assert(state, is_global == nir_variable_is_global(var));
>>>
>>> -   /* Must have exactly one mode set */
>>> -   validate_assert(state, util_bitcount(var->data.mode) == 1);
>>> +   /* Must have exactly one mode set (i.e., is a power of two) */
>>> +   validate_assert(state, (var->data.mode != 0 &&
>>> +                           !(var->data.mode & (var->data.mode - 1))));
>>
>> We actually have two functions in Mesa for this: util_is_power_of_two
>> and _mesa_is_pow_two. Not sure which one is available to this code,
>> but assuming one is, we should use it.
>
> I don't think either is available in its current location, but I'd be in
> favor of having only one in a new location that is always available.
> Any suggestion where that might be?

src/util/... maybe src/util/bitscan.h? Seems like an okay place for it.