-/* FYI: This is the "One-at-a-Time" algorithm by Bob Jenkins */
-/* from requirements by Colin Plumb. */
-/* (http://burtleburtle.net/bob/hash/doobs.html) */
+/* FYI: This is the "One-at-a-Time" algorithm by Bob Jenkins
+ * from requirements by Colin Plumb.
+ * (http://burtleburtle.net/bob/hash/doobs.html) */
+/* The use of a temporary pointer and the casting games
+ * is needed to serve the dual purposes of
+ * (a) the hashed data being interpreted as "unsigned char" (new since 5.8,
+ * a "char" can be either signed or unsigned, depending on the compiler)
+ * (b) catering for old code that uses a "char"
+ *
+ * The "hash seed" feature was added in Perl 5.8.1 to perturb the results
+ * to avoid "algorithmic complexity attacks".
+ *
+ * If USE_HASH_SEED is defined, hash randomisation is done by default
+ * If USE_HASH_SEED_EXPLICIT is defined, hash randomisation is done
+ * only if the environment variable PERL_HASH_SEED is set.
+ * For maximal control, one can define PERL_HASH_SEED.
+ * (see also perl.c:perl_parse()).
+ */
+#ifndef PERL_HASH_SEED
+# if defined(USE_HASH_SEED) || defined(USE_HASH_SEED_EXPLICIT)
+# define PERL_HASH_SEED PL_hash_seed
+# else
+# define PERL_HASH_SEED 0
+# endif
+#endif