(gif_load): Avoid sign extension and thus out of bounds

color indices when accessing raster pixels.

2 files changed, 13 insertions, 4 deletions

diff --git a/src/ChangeLog b/src/ChangeLog
index ea19bf734eb..3eaef5446c6 100644
--- a/src/ChangeLog
+++ b/src/ChangeLog
@@ -1,3 +1,8 @@
+2000-01-01  Gerd Moellmann  <gerd@gnu.org>
+
+        * xfns.c (gif_load): Avoid sign extension and thus out of bounds
+        color indices when accessing raster pixels.
+
 1999-12-31  Gerd Moellmann  <gerd@gnu.org>
 
         * xfns.c: New image functions adapted to Emacs conventions.
diff --git a/src/xfns.c b/src/xfns.c
index c1c1eaf5c75..a1c30944c32 100644
--- a/src/xfns.c
+++ b/src/xfns.c
@@ -9207,6 +9207,7 @@ gif_load (f, img)
   Lisp_Object image;
   int ino, image_left, image_top, image_width, image_height;
   gif_memory_source memsrc;
+  unsigned char *raster;
 
   specified_file = image_spec_value (img->spec, QCfile, NULL);
   specified_data = image_spec_value (img->spec, QCdata, NULL);
@@ -9327,7 +9328,11 @@ gif_load (f, img)
         XPutPixel (ximg, x, y, FRAME_BACKGROUND_PIXEL (f));
     }
 
-  /* Read the GIF image into the X image.  */
+  /* Read the GIF image into the X image.  We use a local variable
+     `raster' here because RasterBits below is a char *, and invites
+     problems with bytes >= 0x80.  */
+  raster = (unsigned char *) gif->SavedImages[ino].RasterBits;
+  
   if (gif->SavedImages[ino].ImageDesc.Interlace)
     {
       static int interlace_start[] = {0, 4, 2, 1};
@@ -9348,8 +9353,7 @@ gif_load (f, img)
           
           for (x = 0; x < image_width; x++)
             {
-              unsigned int i
-                = gif->SavedImages[ino].RasterBits[(y * image_width) + x];
+              int i = raster[(y * image_width) + x];
               XPutPixel (ximg, x + image_left, row + image_top,
                          pixel_colors[i]);
             }
@@ -9362,7 +9366,7 @@ gif_load (f, img)
       for (y = 0; y < image_height; ++y)
         for (x = 0; x < image_width; ++x)
           {
-            unsigned i = gif->SavedImages[ino].RasterBits[y * image_width + x];
+            int i = raster[y * image_width + x];
             XPutPixel (ximg, x + image_left, y + image_top, pixel_colors[i]);
           }
     }