genesis: merge r874 from upstream (sprite corner-case fix)

BizHawk.Emulation.Cores/Consoles/Sega/gpgx/GPGX.cs

@@ -21,7 +21,7 @@ namespace BizHawk.Emulation.Cores.Consoles.Sega.gpgx
 		"",
 		isPorted: true,
 		isReleased: true,
-		portedVersion: "r872",
+		portedVersion: "r874",
 		portedUrl: "https://code.google.com/p/genplus-gx/"
 		)]
 	public class GPGX : IEmulator, ISyncSoundProvider, IVideoProvider

genplus-gx/core/vdp_render.c

@@ -3862,44 +3862,50 @@ void parse_satb_m5(int line)
 
   do
   {
-    /* Read Y position & size from internal SAT */
+    /* Read Y position from internal SAT cache */
     ypos = (q[link] >> im2_flag) & 0x1FF;
-    size = q[link + 1] >> 8;
 
-    /* Sprite height */
-    height = 8 + ((size & 3) << 3);
-
-    /* Y range */
-    ypos = line - ypos;
-
-    /* Sprite is visble on this line ? */
-    if ((ypos >= 0) && (ypos < height))
+    /* Check if sprite Y position has been reached */
+    if (line >= ypos)
     {
-      /* Sprite overflow */
-      if (count == max)
+      /* Read sprite size from internal SAT cache */
+      size = q[link + 1] >> 8;
+
+      /* Sprite height */
+      height = 8 + ((size & 3) << 3);
+
+      /* Y range */
+      ypos = line - ypos;
+
+      /* Check if sprite is visible on current line */
+      if (ypos < height)
       {
-        status |= 0x40;
-        break;
+        /* Sprite overflow */
+        if (count == max)
+        {
+          status |= 0x40;
+          break;
+        }
+
+        /* Update sprite list (only name, attribute & xpos are parsed from VRAM) */ 
+        object_info->attr  = p[link + 2];
+        object_info->xpos  = p[link + 3] & 0x1ff;
+        object_info->ypos  = ypos;
+        object_info->size  = size & 0x0f; 
+
+        /* Increment Sprite count */
+        ++count;
+
+        /* Next sprite entry */
+        object_info++;
       }
-
-      /* Update sprite list (only name, attribute & xpos are parsed from VRAM) */ 
-      object_info->attr  = p[link + 2];
-      object_info->xpos  = p[link + 3] & 0x1ff;
-      object_info->ypos  = ypos;
-      object_info->size  = size & 0x0f; 
-
-      /* Increment Sprite count */
-      ++count;
-
-      /* Next sprite entry */
-      object_info++;
     }
 
-    /* Read link data from internal SAT */ 
+    /* Read link data from internal SAT cache */ 
     link = (q[link + 1] & 0x7F) << 2;
 
-    /* Last sprite */
-    if (link == 0) break;
+    /* Stop parsing if link data points to first entry (#0) or after the last entry (#64 in H32 mode, #80 in H40 mode) */
+    if ((link == 0) || (link >= bitmap.viewport.w)) break;
   }
   while (--total);