CRTC: Make the fix for bug #2054 nicer.

- Simplify the condition (a >= b + 1) to (a > b).
- Split the if/else into 2 if statements with opposite conditions.
- Swap their order because the code in the second can make the condition
  of the first true and in that case we want to execute it (that's what
  the goto did).
- Also get rid of the + 1 in if (ycounter + 1 >= VTOTALADJ) since it was
  wrong - we now nicely got rid of TWO annoying "+ 1"s. 

There was nothing to fix for cases where the VTOTALADJ register > 0,
which is fortunately most/all of the interesting test cases.


git-svn-id: https://svn.code.sf.net/p/vice-emu/code/trunk@45221 379a1393-f5fb-40a0-bcee-ef074d9b53f7

vice/src/crtc/crtc.c

@@ -717,58 +717,8 @@ static void crtc_raster_draw_alarm_handler(CLOCK offset, void *data)
      * The text lines are followed by a bottom border, vertical retrace
      * (which includes vertical sync), and top border. This total number of
      * scan lines is expressed in VTOTAL text lines + VTOTALADJ scan lines.
-     *
-     * Are we past the end of the screen, i.e. the top border?
      */
-    if (crtc.current_charline >= crtc.regs[CRTC_REG_VTOTAL] + 1) {
-#if CRTC_BEAM_RACING
-        if ((crtc.retrace_type & CRTC_RETRACE_TYPE_CRTC) == 0 && /* no CRTC */
-            crtc.current_line == 32*8 + 4 - 1) {
-            /* Set the retrace/vertical blank alarm, to end the IRQ,
-             * at the rhs of the visible text area but 1 line above it.
-             * Non-crtc timings are fixed so we might as well use the
-             * more efficient expression to check for the top line. */
-            alarm_set(crtc.adjusted_retrace_alarm,
-                      crtc.rl_start + crtc.rl_visible);
-        }
-#endif
-        /* The real end is VTOTALADJ scan lines futher down, for fine tuning */
-        if ((crtc.raster.ycounter + 1) >= crtc.regs[CRTC_REG_VTOTALADJ]) {
-hack:
-            long cycles;
-
-            /* Do vsync stuff. Reset line counters to top (0). */
-            /* printf("new screen at clk=%d\n",crtc.rl_start); */
-            crtc_reset_screen_ptr();
-            crtc.raster.ycounter = 0;
-            crtc.current_charline = 0;
-            new_venable = 1;        /* Re-enable video */
-
-            /* expected number of rasterlines for next frame */
-            crtc.framelines = crtc.current_line;
-            crtc.current_line = 0;
-
-            /* hardware cursor handling */
-            if (crtc.crsrmode & 2) {
-                crtc.crsrcnt--;
-                if (!crtc.crsrcnt) {
-                    crtc.crsrcnt = (crtc.crsrmode & 1) ? 16 : 32;
-                    crtc.crsrstate ^= 1;
-                }
-            }
-
-            /* cycles per frame, for speed adjustments */
-            cycles = crtc.rl_start - crtc.frame_start;
-            if (crtc.frame_start && (cycles != crtc.cycles_per_frame)) {
-                machine_set_cycles_per_frame(cycles);
-                crtc.cycles_per_frame = cycles;
-            }
-            crtc.frame_start = crtc.rl_start;
-        } else {
-            crtc.raster.ycounter++;
-            crtc.raster.ycounter &= 0x1f;
-        }
-    } else {
+    if (crtc.current_charline <= crtc.regs[CRTC_REG_VTOTAL]) {
         /* Are we NOT at the bottom most scan line of a character,
          * i.e still inside it? */
         if (crtc.raster.ycounter != crtc.regs[CRTC_REG_SCANLINE]) {
@@ -810,14 +760,6 @@ static void crtc_raster_draw_alarm_handler(CLOCK offset, void *data)
                 }
                 new_vsync++;  /* compensate for the first decrease below */
             }
-            /*
-             * This is a horrible hack and a better flow of control should
-             * be possible!
-             */
-            if (crtc.regs[CRTC_REG_VTOTALADJ] == 0 &&
-                    crtc.current_charline >= crtc.regs[CRTC_REG_VTOTAL] + 1) {
-                goto hack;
-            }
         }
         /* Enable or disable the cursor, if it is in the next character line */
         if (crtc.raster.ycounter == (unsigned int)(crtc.regs[CRTC_REG_CURSORSTART] & 0x1f)) {
@@ -828,6 +770,60 @@ static void crtc_raster_draw_alarm_handler(CLOCK offset, void *data)
 
         crtc.henable = 1;
     }
+    /*
+     * This is not structured as the else-part of the previous condition,
+     * because this condition can become true in the previous then-part.
+     *
+     * Are we past the end of the screen, i.e. the top border?
+     */
+    if (crtc.current_charline > crtc.regs[CRTC_REG_VTOTAL]) {
+#if CRTC_BEAM_RACING
+        if ((crtc.retrace_type & CRTC_RETRACE_TYPE_CRTC) == 0 && /* no CRTC */
+            crtc.current_line == 32*8 + 4 - 1) {
+            /* Set the retrace/vertical blank alarm, to end the IRQ,
+             * at the rhs of the visible text area but 1 line above it.
+             * Non-crtc timings are fixed so we might as well use the
+             * more efficient expression to check for the top line. */
+            alarm_set(crtc.adjusted_retrace_alarm,
+                      crtc.rl_start + crtc.rl_visible);
+        }
+#endif
+        /* The real end is VTOTALADJ scan lines futher down, for fine tuning */
+        if (crtc.raster.ycounter >= crtc.regs[CRTC_REG_VTOTALADJ]) {
+            long cycles;
+
+            /* Do vsync stuff. Reset line counters to top (0). */
+            /* printf("new screen at clk=%d\n",crtc.rl_start); */
+            crtc_reset_screen_ptr();
+            crtc.raster.ycounter = 0;
+            crtc.current_charline = 0;
+            new_venable = 1;        /* Re-enable video */
+
+            /* expected number of rasterlines for next frame */
+            crtc.framelines = crtc.current_line;
+            crtc.current_line = 0;
+
+            /* hardware cursor handling */
+            if (crtc.crsrmode & 2) {
+                crtc.crsrcnt--;
+                if (!crtc.crsrcnt) {
+                    crtc.crsrcnt = (crtc.crsrmode & 1) ? 16 : 32;
+                    crtc.crsrstate ^= 1;
+                }
+            }
+
+            /* cycles per frame, for speed adjustments */
+            cycles = crtc.rl_start - crtc.frame_start;
+            if (crtc.frame_start && (cycles != crtc.cycles_per_frame)) {
+                machine_set_cycles_per_frame(cycles);
+                crtc.cycles_per_frame = cycles;
+            }
+            crtc.frame_start = crtc.rl_start;
+        } else {
+            crtc.raster.ycounter++;
+            crtc.raster.ycounter &= 0x1f;
+        }
+    }
     /* If we're in the vertical sync area, count down how many lines are left. */
     if (new_vsync) {
         new_vsync--;