* xterm.c (x_alloc_nearest_color_1): Use a more-precise algorithm

for nearest color, one that neither overflows nor relies on unsigned
arithmetic.

2 files changed, 11 insertions, 5 deletions

diff --git a/src/ChangeLog b/src/ChangeLog
index ff6945d8656..125028297d1 100644
--- a/src/ChangeLog
+++ b/src/ChangeLog
@@ -1,5 +1,9 @@
 2011-06-13  Paul Eggert  <eggert@cs.ucla.edu>
 
+        * xterm.c (x_alloc_nearest_color_1): Use a more-precise algorithm
+        for nearest color, one that neither overflows nor relies on unsigned
+        arithmetic.
+
         Remove unnecessary casts.
         * xterm.c (x_term_init):
         * xfns.c (x_set_border_pixel):
diff --git a/src/xterm.c b/src/xterm.c
index 85c19ed16af..1c1c8e3f107 100644
--- a/src/xterm.c
+++ b/src/xterm.c
@@ -1693,16 +1693,18 @@ x_alloc_nearest_color_1 (Display *dpy, Colormap cmap, XColor *color)
          a least-squares matching, which is what X uses for closest
          color matching with StaticColor visuals.  */
       int nearest, i;
-      unsigned long nearest_delta = ~ (unsigned long) 0;
+      int max_color_delta = (1 << (16 - 2)) - 1;
+      int max_delta = 3 * max_color_delta;
+      int nearest_delta = max_delta + 1;
       int ncells;
       const XColor *cells = x_color_cells (dpy, &ncells);
 
       for (nearest = i = 0; i < ncells; ++i)
         {
-          long dred   = (color->red   >> 8) - (cells[i].red   >> 8);
-          long dgreen = (color->green >> 8) - (cells[i].green >> 8);
-          long dblue  = (color->blue  >> 8) - (cells[i].blue  >> 8);
-          unsigned long delta = dred * dred + dgreen * dgreen + dblue * dblue;
+          int dred   = (color->red   >> 2) - (cells[i].red   >> 2);
+          int dgreen = (color->green >> 2) - (cells[i].green >> 2);
+          int dblue  = (color->blue  >> 2) - (cells[i].blue  >> 2);
+          int delta = dred * dred + dgreen * dgreen + dblue * dblue;
 
           if (delta < nearest_delta)
             {