Merge branch 'PHP-7.4'

* PHP-7.4:
  Fix #79615: Wrong GIF header written in GD GIFEncode

Author: cmb69

ext/gd/libgd/gd_gif_out.c

@@ -333,7 +333,7 @@ GIFEncode(gdIOCtxPtr fp, int GWidth, int GHeight, int GInterlace, int Background
         /*
          * OR in the resolution
          */
-        B |= (Resolution - 1) << 5;
+        B |= (Resolution - 1) << 4;
 
         /*
          * OR in the Bits per Pixel

ext/gd/tests/bug79615.phpt

@@ -0,0 +1,20 @@
+--TEST--
+Bug #79615 (Wrong GIF header written in GD GIFEncode)
+--SKIPIF--
+<?php
+if (!extension_loaded('gd')) die('skip gd extension not available');
+?>
+--FILE--
+<?php
+$im = imagecreate(3, 3); // 3x3, 9 colors, 4 bits per pixel
+for ($x = 0; $x < 3; $x++) {
+    for ($y = 0; $y < 3; $y++) {
+        imagesetpixel($im, $x, $y, imagecolorallocate($im, $x, $y, 0));
+    }
+}
+ob_start();
+imagegif($im);
+echo decbin(ord(ob_get_clean()[0xA]));
+?>
+--EXPECT--
+10110011