add skpdiff tool to compare bitmaps

experimental/skpdiff/skpdiff_util.h

Index: experimental/skpdiff/skpdiff_util.h
diff --git a/experimental/skpdiff/skpdiff_util.h b/experimental/skpdiff/skpdiff_util.h
new file mode 100644
index 0000000000000000000000000000000000000000..40d97266e100785d2a34f19b7df0f817184ea56f
--- /dev/null
+++ b/experimental/skpdiff/skpdiff_util.h
@@ -0,0 +1,31 @@
+#ifndef skpdiff_util_DEFINED
+#define skpdiff_util_DEFINED
+
+#include <vector>
+#include <string>
+#include <CL/cl.h>
+
+/**
+ * Converts an OpenCL error number into the string of its enumeration name.
+ * @param  err The OpenCL error number
+ * @return The string of the name of the error; "UNKOWN" if the error number is invalid
+ */
+const char* cl_error_to_string(cl_int err);
+
+/**
+ * Get a positive monotonic real-time measure of the amount of seconds since some undefined epoch.
+ * Maximum precision is the goal of this routine.
+ * @return Amount of time in seconds since some epoch
+ */
+double get_seconds();
+
+/**
+ * Get file entries of the given directory.
+ * @param  path    A path to a directory to enumerate
+ * @param  entries A vector to return the results into
+ * @return         True on success, false otherwise
+ */
+bool get_directory(const char path[], std::vector<std::string>* entries);
+
+
+#endif