llvmpipe: doc fixes

Reviewed-by: Jose Fonseca <jose.fonseca@broadcom.com>
Reviewed-by: Roland Scheidegger <roland.scheidegger@broadcom.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/37986>

src/gallium/auxiliary/gallivm/lp_bld_arit.c

@@ -1132,8 +1132,9 @@ lp_build_div(struct lp_build_context *bld,
 /**
  * Linear interpolation helper.
  *
- * @param normalized whether we are interpolating normalized values,
- *        encoded in normalized integers, twice as wide.
+ * @param flags
+ *        LP_BLD_LERP_WIDE_NORMALIZED: whether we are interpolating normalized
+ *        values, encoded in normalized integers, twice as wide.
  *
  * @sa http://www.stereopsis.com/doubleblend.html
  */
@@ -1191,9 +1192,9 @@ lp_build_lerp_simple(struct lp_build_context *bld,
          }
       } else {
          /*
-          * The rescaling trick above doesn't work for signed numbers, so
-          * use the 2**n - 1 divison approximation in lp_build_mul_norm
-          * instead.
+          * Scale x from [0, 2**n - 1] to [0, 2**n] by adding the
+          * most-significant-bit to the lowest-significant-bit, so that
+          * later we can just divide by 2**n instead of 2**n - 1.
           */
          assert(!(flags & LP_BLD_LERP_PRESCALED_WEIGHTS));
          res = lp_build_mul_norm(bld->gallivm, bld->type, x, delta);
@@ -1228,8 +1229,8 @@ lp_build_lerp_simple(struct lp_build_context *bld,
          /*
           * We need to mask out the high order bits when lerping 8bit
           * normalized colors stored on 16bits
-          */
-         /* XXX: This step is necessary for lerping 8bit colors stored on
+          *
+          * XXX: This step is necessary for lerping 8bit colors stored on
           * 16bits, but it will be wrong for true fixed point use cases.
           * Basically we need a more powerful lp_type, capable of further
           * distinguishing the values interpretation from the value storage.

src/gallium/auxiliary/gallivm/lp_bld_sample_aos.c

@@ -546,7 +546,7 @@ lp_build_sample_image_nearest(struct lp_build_sample_context *bld,
 
 /**
  * Fetch texels for image with linear sampling.
- * Return filtered color as two vectors of 16-bit fixed point values.
+ * Return filtered color as one vectors of 8-bit unorm values.
  */
 static void
 lp_build_sample_fetch_image_linear(struct lp_build_sample_context *bld,
@@ -581,7 +581,7 @@ lp_build_sample_fetch_image_linear(struct lp_build_sample_context *bld,
     *
     * where each value is between 0 and 0xff,
     *
-    * into one 16 x i20
+    * into one 16 x i8
     *
     *   s_fpart = {s0, s0, s0, s0, s1, s1, s1, s1, s2, s2, s2, s2, s3, s3, s3, s3}
     *
@@ -628,13 +628,6 @@ lp_build_sample_fetch_image_linear(struct lp_build_sample_context *bld,
     * bit cast them into 16 x u8
     *
     *   r0 g0 b0 a0 r1 g1 b1 a1 r2 g2 b2 a2 r3 g3 b3 a3
-    *
-    * unpack them into two 8 x i16:
-    *
-    *   r0 g0 b0 a0 r1 g1 b1 a1
-    *   r2 g2 b2 a2 r3 g3 b3 a3
-    *
-    * The higher 8 bits of the resulting elements will be zero.
     */
    numj = 1 + (dims >= 2);
    numk = 1 + (dims >= 3);
@@ -677,7 +670,7 @@ lp_build_sample_fetch_image_linear(struct lp_build_sample_context *bld,
    }
 
    /*
-    * Linear interpolation with 8.8 fixed point.
+    * Linear interpolation with 8-bit unorm.
     */
 
    /* general 1/2/3-D lerping */
@@ -726,7 +719,7 @@ lp_build_sample_fetch_image_linear(struct lp_build_sample_context *bld,
 
 /**
  * Sample a single texture image with (bi-)(tri-)linear sampling.
- * Return filtered color as two vectors of 16-bit fixed point values.
+ * Return filtered color as a vector of 8-bit unorm values.
  */
 static void
 lp_build_sample_image_linear(struct lp_build_sample_context *bld,

src/gallium/auxiliary/gallivm/lp_bld_sample_soa.c

@@ -3641,7 +3641,7 @@ lp_build_sample_soa_code(struct gallivm_state *gallivm,
            (bld.num_lods == 1 ||
             derived_sampler_state.min_img_filter == derived_sampler_state.mag_img_filter))) {
          if (use_aos) {
-            /* do sampling/filtering with fixed pt arithmetic */
+            /* do sampling/filtering with 8-bit unorm arithmetic */
             lp_build_sample_aos(&bld,
                                 newcoords[0], newcoords[1],
                                 newcoords[2],
@@ -3792,7 +3792,7 @@ lp_build_sample_soa_code(struct gallivm_state *gallivm,
             }
 
             if (use_aos) {
-               /* do sampling/filtering with fixed pt arithmetic */
+               /* do sampling/filtering with 8-bit arithmetic */
                lp_build_sample_aos(&bld4,
                                    s4, t4, r4, offsets4,
                                    lod_positive4, lod_fpart4,