draw,util: Refactor draw_overflow_uadd into util.

So it can be used outside draw.  Also drop  the overflow_value parameter,
as it wasn't meaningfully useful.

Reviewed-by: Brian Paul <brianp@vmware.com>
Reviewed-by: Roland Scheidegger <sroland@vmware.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/19683>

src/gallium/auxiliary/draw/draw_private.h

@@ -588,21 +588,4 @@ draw_clamp_viewport_idx(int idx)
    return ((PIPE_MAX_VIEWPORTS > idx && idx >= 0) ? idx : 0);
 }
 
-
-/**
- * Adds two unsigned integers and if the addition
- * overflows then it returns the value from
- * the overflow_value variable.
- */
-static inline unsigned
-draw_overflow_uadd(unsigned a, unsigned b,
-                   unsigned overflow_value)
-{
-   unsigned res = a + b;
-   if (res < a) {
-      res = overflow_value;
-   }
-   return res;
-}
-
 #endif /* DRAW_PRIVATE_H */

src/gallium/auxiliary/draw/draw_pt.c

@@ -360,13 +360,9 @@ prim_restart_loop(struct draw_context *draw,
    struct pipe_draw_start_count_bias cur = *draw_info;
    cur.count = 0;
 
-   /* The largest index within a loop using the i variable as the index.
-    * Used for overflow detection */
-   const unsigned MAX_LOOP_IDX = 0xffffffff;
-
    for (unsigned j = 0; j < draw_info->count; j++) {
       unsigned index = 0;
-      unsigned i = draw_overflow_uadd(draw_info->start, j, MAX_LOOP_IDX);
+      unsigned i = util_clamped_uadd(draw_info->start, j);
       if (i < elt_max) {
          switch (draw->pt.user.eltSize) {
          case 1:

src/gallium/auxiliary/draw/draw_pt_vsplit.c

@@ -33,9 +33,6 @@
 #define SEGMENT_SIZE 1024
 #define MAP_SIZE     256
 
-/* The largest possible index within an index buffer */
-#define MAX_ELT_IDX 0xffffffff
-
 struct vsplit_frontend {
    struct draw_pt_front_end base;
    struct draw_context *draw;
@@ -116,7 +113,7 @@ vsplit_add_cache(struct vsplit_frontend *vsplit, unsigned fetch)
 static inline unsigned
 vsplit_get_base_idx(unsigned start, unsigned fetch)
 {
-   return draw_overflow_uadd(start, fetch, MAX_ELT_IDX);
+   return util_clamped_uadd(start, fetch);
 }
 
 

src/util/u_math.h

@@ -809,6 +809,20 @@ util_quantize_lod_bias(float lod)
    return roundf(lod * 256) / 256;
 }
 
+/**
+ * Adds two unsigned integers and if the addition
+ * overflows then clamp it to ~0U.
+ */
+static inline unsigned
+util_clamped_uadd(unsigned a, unsigned b)
+{
+   unsigned res = a + b;
+   if (res < a) {
+      res = ~0U;
+   }
+   return res;
+}
+
 #ifdef __cplusplus
 }
 #endif