# HG changeset patch
# User Paul Boddie <paul@boddie.org.uk>
# Date 1541344498 -3600
# Node ID 6d95b67997e657cdb4473d13ebffa2c4d83ea40c
# Parent  9d30c6982e8d975ae4a35da8f59c67745f7ae084
Introduced various pointer address wrapping functions.

diff -r 9d30c6982e8d -r 6d95b67997e6 include/display.h
--- a/include/display.h	Sun Nov 04 15:46:13 2018 +0100
+++ b/include/display.h	Sun Nov 04 16:14:58 2018 +0100
@@ -115,4 +115,10 @@
 
 void scroll_display(display_config_t *cfg, int x, int y);
 
+/* Address-related functions. */
+
+uint8_t *wrap_pointer(uint8_t *ptr, uint8_t *lower, uint8_t *upper);
+
+uint8_t *wrap_screen_pointer(display_config_t *cfg, uint8_t *ptr);
+
 #endif /* __DISPLAY_H__ */
diff -r 9d30c6982e8d -r 6d95b67997e6 lib/display.c
--- a/lib/display.c	Sun Nov 04 15:46:13 2018 +0100
+++ b/lib/display.c	Sun Nov 04 16:14:58 2018 +0100
@@ -147,10 +147,7 @@
                 0x00;
         }
 
-        linedata += cfg->line_length;
-
-        if (linedata >= cfg->screen_limit)
-            linedata -= cfg->screen_size;
+        linedata = wrap_screen_pointer(cfg, linedata + cfg->line_length);
     }
 }
 
@@ -172,7 +169,7 @@
 {
     int sx, sy, dx, dy;
     uint8_t *storeline = store + ystart * width,
-            *displayline = cfg->screen_start + y * cfg->line_length,
+            *displayline = wrap_screen_pointer(cfg, cfg->screen_start + y * cfg->line_length),
             pixel;
 
     /* Define the limits of the copying in the store. */
@@ -189,9 +186,6 @@
 
     for (sy = ystart, dy = y; (sy < ylimit) && (dy < cfg->line_count); sy++, dy++)
     {
-        if (displayline >= cfg->screen_limit)
-            displayline -= cfg->screen_size;
-
         for (sx = xstart, dx = x; (sx < xlimit) && (dx < cfg->line_length); sx++, dx++)
         {
             if (to_display)
@@ -205,7 +199,7 @@
         }
 
         storeline += width;
-        displayline += cfg->line_length;
+        displayline = wrap_screen_pointer(cfg, displayline + cfg->line_length);
     }
 }
 
@@ -213,21 +207,30 @@
 
 void scroll_display(display_config_t *cfg, int x, int y)
 {
-    uint8_t *start;
-
-    /* Move the screen start by the given number of bytes and lines. */
+    /* Move the screen start by the given number of bytes and lines, wrapping
+       around the start and end of the framebuffer. */
 
-    start = cfg->screen_start + x + y * cfg->line_length;
+    cfg->screen_start = wrap_screen_pointer(cfg, cfg->screen_start + x +
+                                                 y * cfg->line_length);
+}
 
-    /* Wrap around the start of the framebuffer to the end. */
+/* Wrap a pointer within the given limits. */
+
+uint8_t *wrap_pointer(uint8_t *ptr, uint8_t *lower, uint8_t *upper)
+{
+    uint32_t size = upper - lower;
 
-    if (start < cfg->frame_start)
-        start = cfg->screen_limit - (cfg->frame_start - start) % cfg->screen_size;
-
-    /* Wrap around the end of the framebuffer to the start. */
+    if (ptr < lower)
+        return upper - (lower - ptr) % size;
+    else if (ptr >= upper)
+        return lower + (ptr - upper) % size;
+    else
+        return ptr;
+}
 
-    else if (start >= cfg->screen_limit)
-        start = cfg->frame_start + (start - cfg->screen_limit) % cfg->screen_size;
+/* Wrap the screen pointer to the current frame. */
 
-    cfg->screen_start = start;
+uint8_t *wrap_screen_pointer(display_config_t *cfg, uint8_t *ptr)
+{
+    return wrap_pointer(ptr, cfg->frame_start, cfg->screen_limit);
 }