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

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

diff --git a/src/ChangeLog b/src/ChangeLog
index ff6945d865693961e527d93ff71d818f0b074e23..125028297d13e671d5c16e76104ba07ae2117634 100644 (file)
--- 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 85c19ed16afd0c73f35b9ad43052c05669b9aa75..1c1c8e3f1073c9bfa20ffe374cce68fc4ba385a3 100644 (file)
--- 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)
            {