From: Paul Eggert <eggert@cs.ucla.edu>
Date: Mon, 13 Jun 2011 07:53:14 +0000 (-0700)
Subject: * xterm.c (x_alloc_nearest_color_1): Use a more-precise algorithm
X-Git-Tag: emacs-pretest-24.0.90~104^2~548^2~22
X-Git-Url: http://git.eshelyaron.com/gitweb/?a=commitdiff_plain;h=5efd304be978e2c0b3b1ac0c39b303b8d094ab66;p=emacs.git

* 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 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)
 	    {