gallivm: optimize soa linear clamp to edge wrap mode a bit

Clamp against 0 instead of -0.5, which simplifies things.
The former version would have resulted in both int coords being zero
(in case of coord being smaller than 0) and some "unused" weight value,
whereas now the int coords will be 0 and 1, but weight will be 0, hence the
lerp should produce the same value.
Still not happy about differences between normalized and non-normalized...

diff --git a/src/gallium/auxiliary/gallivm/lp_bld_sample_soa.c b/src/gallium/auxiliary/gallivm/lp_bld_sample_soa.c
index b020782..f3c4b6a 100644 (file)
--- a/src/gallium/auxiliary/gallivm/lp_bld_sample_soa.c
+++ b/src/gallium/auxiliary/gallivm/lp_bld_sample_soa.c
@@ -288,30 +288,37 @@ lp_build_sample_wrap_linear(struct lp_build_sample_context *bld,
       break;
 
    case PIPE_TEX_WRAP_CLAMP_TO_EDGE:
-      if (bld->static_state->normalized_coords) {
-         /* clamp to [0,1] */
-         coord = lp_build_clamp(coord_bld, coord, coord_bld->zero, coord_bld->one);
-         /* mul by tex size and subtract 0.5 */
-         coord = lp_build_mul(coord_bld, coord, length_f);
-         coord = lp_build_sub(coord_bld, coord, half);
-      }
-      /* XXX this is odd normalized ranges from -0.5 to length-0.5 after denorm
-         but non-normalized ranges from to 0.5 to length-0.5 after clamp */
-      else {
-         LLVMValueRef min, max;
-         /* clamp to [0.5, length - 0.5] */
-         min = half;
-         max = lp_build_sub(coord_bld, length_f, min);
-         coord = lp_build_clamp(coord_bld, coord, min, max);
+      {
+         struct lp_build_context abs_coord_bld = bld->coord_bld;
+         abs_coord_bld.type.sign = FALSE;
+
+         if (bld->static_state->normalized_coords) {
+            /* mul by tex size */
+            coord = lp_build_mul(coord_bld, coord, length_f);
+            /* clamp to length max */
+            coord = lp_build_min(coord_bld, coord, length_f);
+            /* subtract 0.5 */
+            coord = lp_build_sub(coord_bld, coord, half);
+            /* clamp to [0, length - 0.5] */
+            coord = lp_build_max(coord_bld, coord, coord_bld->zero);
+         }
+         /* XXX this is odd normalized ranges from 0 to length-0.5 after denorm
+            but non-normalized ranges from to 0.5 to length-0.5 after clamp.
+            Is this missing the sub 0.5? */
+         else {
+            LLVMValueRef min, max;
+            /* clamp to [0.5, length - 0.5] */
+            min = half;
+            max = lp_build_sub(coord_bld, length_f, min);
+            coord = lp_build_clamp(coord_bld, coord, min, max);
+         }
+         /* convert to int, compute lerp weight */
+         lp_build_ifloor_fract(&abs_coord_bld, coord, &coord0, &weight);
+         coord1 = lp_build_add(int_coord_bld, coord0, int_coord_bld->one);
+         /* coord1 = min(coord1, length-1) */
+         coord1 = lp_build_min(int_coord_bld, coord1, length_minus_one);
+         break;
       }
-      /* convert to int, compute lerp weight */
-      lp_build_ifloor_fract(coord_bld, coord, &coord0, &weight);
-      coord1 = lp_build_add(int_coord_bld, coord0, int_coord_bld->one);
-      /* coord0 = max(coord0, 0) */
-      coord0 = lp_build_max(int_coord_bld, coord0, int_coord_bld->zero);
-      /* coord1 = min(coord1, length-1) */
-      coord1 = lp_build_min(int_coord_bld, coord1, length_minus_one);
-      break;
 
    case PIPE_TEX_WRAP_CLAMP_TO_BORDER:
       {