On 06/02/2011 06:43 AM, Benjamin Bellec wrote:
Hello,
I performed several tests of the logbase2() function.
This function is defined and used in these files:
src/mesa/main/teximage.c
src/mesa/drivers/dri/intel/intel_tex_image.c
src/mesa/drivers/dri/unichrome/via_tex.c
src/mesa/drivers/dri/i965/intel_tex_image.c
src/mesa/drivers/dri/tdfx/tdfx_tex.c
There is also a util_logbase2() function in
src/gallium/auxiliary/util/u_math.c which do the same thing.
Both functions from "src/mesa/main/teximage.c" and
"src/gallium/auxiliary/util/u_math.c" are called when I play to ETQW
with r600g.
First thing: is it possible to merge this function in one place? The
same function is implement in different place. I have no sufficient
experience of the Mesa architecture to answer this myself.
Second thing: there is a C implementation in Wikipedia (
http://en.wikipedia.org/wiki/Binary_logarithm#Algorithm ), I merged it
in Mesa and I noted that it is *at least* twice faster than logbase2()
and util_logbase2() (with or without GCC optimization).
Third thing: I think it's better to use an unsigned int than a int for
the logbase2's parameter. At least in "teximage.c" and
"intel_tex_image.c", the result is stored in a GLuint. But not in
"via_tex.c"
Here is a patch to merge it, at least in "src/mesa/main/teximage.c". I
will understand any comments, especially on the relevance of this patch.
(The patch still uses a integer parameter).
Thanks for the patch.
AFAIK, the logbase2() function isn't called from any hot-spot code so
the performance of it isn't critical. But who knows if that might
change in the future.
I'll commit the patch in a bit.
There is some duplication of utility code between Mesa and Gallium.
At some point we'll probably start consolidating it.
-Brian
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