Add a wrapper for 'memmem'

memmem is a GNU libc extension that works like strstr except that the
size of the needle and the haystack are passed into the function
instead of using null-terminated strings.

This patch adds a wrapper function called 'cogl_util_memmem' so that
we can use this function. There is a configure check and if the
function is not available then a fallback implementation will be used.
Otherwise cogl_util_memmem is just defined to memmem.

Reviewed-by: Robert Bragg <robert@linux.intel.com>

(cherry picked from commit 1dd1b0a67f6238e13f7f9253fb03addada0541b7)

cogl/cogl-util.c

@@ -25,6 +25,8 @@
 #include "config.h"
 #endif
 
+#include <string.h>
+
 #include "cogl-util.h"
 #include "cogl-private.h"
 
@@ -252,4 +254,26 @@ _cogl_util_pixel_format_from_masks (unsigned long r_mask,
   return image_format;
 }
 
+#ifndef HAVE_MEMMEM
+
+char *
+_cogl_util_memmem (const void *haystack,
+                   size_t haystack_len,
+                   const void *needle,
+                   size_t needle_len)
+{
+  size_t i;
+
+  if (needle_len > haystack_len)
+    return NULL;
+
+  for (i = 0; i <= haystack_len - needle_len; i++)
+    if (!memcmp ((const char *) haystack + i, needle, needle_len))
+      return (char *) haystack + i;
+
+  return NULL;
+}
+
+#endif /* HAVE_MEMMEM */
+
 #endif /* _COGL_IN_TEST_BITMASK */