Revert "llvmpipe: increase number of subpixel bits to eight"

This reverts commit 755c11dc5e.
We agreed that this is band-aid that's not very useful and
the proper solution is to rewrite the rasterization algo
so that it operates on 64 bit values.

Signed-off-by: Zack Rusin <zackr@vmware.com>

src/gallium/drivers/llvmpipe/lp_rast.h

@@ -46,20 +46,10 @@ struct lp_scene;
 struct lp_fence;
 struct cmd_bin;
 
-#define FIXED_TYPE_WIDTH 32
 /** For sub-pixel positioning */
-#define FIXED_ORDER 8
+#define FIXED_ORDER 4
 #define FIXED_ONE (1<<FIXED_ORDER)
 
-/** Maximum length of an edge in a primitive in pixels.
- *  If the framebuffer is large we have to think about fixed-point
- *  integer overflow.  Coordinates need ((FIXED_TYPE_WIDTH/2) - 1) bits
- *  to be able to fit product of two such coordinates inside
- *  FIXED_TYPE_WIDTH, any larger and we could overflow a
- *  FIXED_TYPE_WIDTH_-bit int.
- */
-#define MAX_FIXED_LENGTH (1 << (((FIXED_TYPE_WIDTH/2) - 1) - FIXED_ORDER))
-
 /* Rasterizer output size going to jit fs, width/height */
 #define LP_RASTER_BLOCK_SIZE 4
 

src/gallium/drivers/llvmpipe/lp_setup.c

@@ -1007,12 +1007,16 @@ try_update_scene_state( struct lp_setup_context *setup )
                                          &setup->draw_regions[i]);
          }
       }
-      /*
-       * Check if subdivision of triangles is needed if the framebuffer
-       * is larger than our MAX_FIXED_LENGTH can accomodate.
+      /* If the framebuffer is large we have to think about fixed-point
+       * integer overflow.  For 2K by 2K images, coordinates need 15 bits
+       * (2^11 + 4 subpixel bits).  The product of two such numbers would
+       * use 30 bits.  Any larger and we could overflow a 32-bit int.
+       *
+       * To cope with this problem we check if triangles are large and
+       * subdivide them if needed.
        */
-      setup->subdivide_large_triangles = (setup->fb.width > MAX_FIXED_LENGTH &&
-                                          setup->fb.height > MAX_FIXED_LENGTH);
+      setup->subdivide_large_triangles = (setup->fb.width > 2048 &&
+                                          setup->fb.height > 2048);
    }
                                       
    setup->dirty = 0;

src/gallium/drivers/llvmpipe/lp_setup_tri.c

@@ -995,7 +995,7 @@ check_subdivide_triangle(struct lp_setup_context *setup,
                          const float (*v2)[4],
                          triangle_func_t tri)
 {
-   const float maxLen = MAX_FIXED_LENGTH;  /* longest permissible edge, in pixels */
+   const float maxLen = 2048.0f;  /* longest permissible edge, in pixels */
    float dx10, dy10, len10;
    float dx21, dy21, len21;
    float dx02, dy02, len02;