util: treat denorm'ed floats like zero

The D3D10 spec is very explicit about treatment of denorm floats and
the behavior is exactly the same for them as it would be for -0 or
+0. This makes our shading code match that behavior, since OpenGL
doesn't care and on a few cpu's it's faster (worst case the same).
Float16 conversions will likely break but we'll fix them in a follow
up commit.

Signed-off-by: Zack Rusin <[email protected]>
Reviewed-by: Jose Fonseca <[email protected]>
Reviewed-by: Roland Scheidegger <[email protected]>

2 files changed, 11 insertions, 0 deletions

diff --git a/src/gallium/drivers/llvmpipe/lp_rast.c b/src/gallium/drivers/llvmpipe/lp_rast.c
index 871cc50fb4c..e172dac40cb 100644
--- a/src/gallium/drivers/llvmpipe/lp_rast.c
+++ b/src/gallium/drivers/llvmpipe/lp_rast.c
@@ -751,6 +751,12 @@ static PIPE_THREAD_ROUTINE( thread_function, init_data )
    struct lp_rasterizer_task *task = (struct lp_rasterizer_task *) init_data;
    struct lp_rasterizer *rast = task->rast;
    boolean debug = false;
+   unsigned fpstate = util_fpstate_get();
+
+   /* Make sure that denorms are treated like zeros. This is 
+    * the behavior required by D3D10. OpenGL doesn't care.
+    */
+   util_fpstate_set_denorms_to_zero(fpstate);
 
    while (1) {
       /* wait for work */
diff --git a/src/gallium/drivers/llvmpipe/lp_test_main.c b/src/gallium/drivers/llvmpipe/lp_test_main.c
index 4c610923146..8a896becf53 100644
--- a/src/gallium/drivers/llvmpipe/lp_test_main.c
+++ b/src/gallium/drivers/llvmpipe/lp_test_main.c
@@ -370,6 +370,11 @@ int main(int argc, char **argv)
    unsigned i;
    boolean success;
    boolean single = FALSE;
+   unsigned fpstate;
+
+   util_cpu_detect();
+   fpstate = util_fpstate_get();
+   util_fpstate_set_denorms_to_zero(fpstate);
 
    for(i = 1; i < argc; ++i) {
       if(strcmp(argv[i], "-v") == 0)