From 0a6c227d6412b01cf2ca45cd21b90384e7fe99c3 Mon Sep 17 00:00:00 2001
From: Ben Campbell <ben@scumways.com>
Date: Wed, 13 Jul 2016 15:05:47 +1200
Subject: FindGIF: Detect version from GIF 4.1.6 and above

GIF 4.1.6 introduced version macros in the header file.  Use them
to get a full version.

Fixes #16196.
---
 Modules/FindGIF.cmake | 46 +++++++++++++++++++++++++++++++++++-----------
 1 file changed, 35 insertions(+), 11 deletions(-)

diff --git a/Modules/FindGIF.cmake b/Modules/FindGIF.cmake
index 7bbb8cf..6fbe9e9 100644
--- a/Modules/FindGIF.cmake
+++ b/Modules/FindGIF.cmake
@@ -2,12 +2,18 @@
 # FindGIF
 # -------
 #
+# This finds the GIF library (giflib)
 #
+# The module defines the following variables:
 #
-# This module searches giflib and defines GIF_LIBRARIES - libraries to
-# link to in order to use GIF GIF_FOUND, if false, do not try to link
-# GIF_INCLUDE_DIR, where to find the headers GIF_VERSION, reports either
-# version 4 or 3 (for everything before version 4)
+# ``GIF_FOUND``
+#   True if giflib was found
+# ``GIF_LIBRARIES``
+#   Libraries to link to in order to use giflib
+# ``GIF_INCLUDE_DIR``
+#   where to find the headers
+# ``GIF_VERSION``
+#   3, 4 or a full version string (eg 5.1.4) for versions >= 4.1.6
 #
 # The minimum required version of giflib can be specified using the
 # standard syntax, e.g.  find_package(GIF 4)
@@ -29,7 +35,7 @@
 #  License text for the above reference.)
 
 # Created by Eric Wing.
-# Modifications by Alexander Neundorf
+# Modifications by Alexander Neundorf, Ben Campbell
 
 find_path(GIF_INCLUDE_DIR gif_lib.h
   HINTS
@@ -61,22 +67,40 @@ set(GIF_LIBRARIES ${GIF_LIBRARY})
 # to be always " Version 2.0, " in versions 3.x of giflib.
 # In version 4 the member UserData was added to GifFileType, so we check for this
 # one.
-# http://giflib.sourcearchive.com/documentation/4.1.4/files.html
+# Versions after 4.1.6 define GIFLIB_MAJOR, GIFLIB_MINOR, and GIFLIB_RELEASE
+# see http://giflib.sourceforge.net/gif_lib.html#compatibility
 if(GIF_INCLUDE_DIR)
   include(${CMAKE_CURRENT_LIST_DIR}/CMakePushCheckState.cmake)
   include(${CMAKE_CURRENT_LIST_DIR}/CheckStructHasMember.cmake)
   CMAKE_PUSH_CHECK_STATE()
   set(CMAKE_REQUIRED_QUIET ${GIF_FIND_QUIETLY})
-  set(GIF_VERSION 3)
   set(CMAKE_REQUIRED_INCLUDES "${GIF_INCLUDE_DIR}")
-  CHECK_STRUCT_HAS_MEMBER(GifFileType UserData gif_lib.h GIF_GifFileType_UserData )
-  if(GIF_GifFileType_UserData)
-    set(GIF_VERSION 4)
+
+  # Check for the specific version defines (>=4.1.6 only)
+  file(STRINGS ${GIF_INCLUDE_DIR}/gif_lib.h _GIF_DEFS REGEX "^[ \t]*#define[ \t]+GIFLIB_(MAJOR|MINOR|RELEASE)")
+  if(_GIF_DEFS)
+    # yay - got exact version info
+    string(REGEX REPLACE ".*GIFLIB_MAJOR ([0-9]+).*" "\\1" _GIF_MAJ "${_GIF_DEFS}")
+    string(REGEX REPLACE ".*GIFLIB_MINOR ([0-9]+).*" "\\1" _GIF_MIN "${_GIF_DEFS}")
+    string(REGEX REPLACE ".*GIFLIB_RELEASE ([0-9]+).*" "\\1" _GIF_REL "${_GIF_DEFS}")
+    set(GIF_VERSION "${_GIF_MAJ}.${_GIF_MIN}.${_GIF_REL}")
+  else()
+    # use UserData field to sniff version instead
+    CHECK_STRUCT_HAS_MEMBER(GifFileType UserData gif_lib.h GIF_GifFileType_UserData )
+    if(GIF_GifFileType_UserData)
+      set(GIF_VERSION 4)
+    else()
+      set(GIF_VERSION 3)
+    endif()
   endif()
+
+  unset(_GIF_MAJ)
+  unset(_GIF_MIN)
+  unset(_GIF_REL)
+  unset(_GIF_DEFS)
   CMAKE_POP_CHECK_STATE()
 endif()
 
-
 # handle the QUIETLY and REQUIRED arguments and set GIF_FOUND to TRUE if
 # all listed variables are TRUE
 include(${CMAKE_CURRENT_LIST_DIR}/FindPackageHandleStandardArgs.cmake)
-- 
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