1 files changed, 39 insertions, 2 deletions
diff --git a/erts/emulator/beam/erl_process.h b/erts/emulator/beam/erl_process.h
index 6118c671ee..0d6b512f78 100644
--- a/erts/emulator/beam/erl_process.h
+++ b/erts/emulator/beam/erl_process.h
@@ -1230,9 +1230,10 @@ void erts_check_for_holes(Process* p);
 
 /* The sequential tracing token is a tuple of size 5:
  *
- *    {Flags, Label, Serial, Sender}
+ *    {Flags, Label, Serial, Sender, LastCnt}
+ *
+ *  WARNING: The top 5-tuple is *MUTABLE* and thus INTERNAL ONLY.
  */
-
 #define SEQ_TRACE_TOKEN_ARITY(p)    (arityval(*(tuple_val(SEQ_TRACE_TOKEN(p)))))
 #define SEQ_TRACE_TOKEN_FLAGS(p)    (*(tuple_val(SEQ_TRACE_TOKEN(p)) + 1))
 #define SEQ_TRACE_TOKEN_LABEL(p)    (*(tuple_val(SEQ_TRACE_TOKEN(p)) + 2))
@@ -2631,6 +2632,9 @@ void erts_notify_inc_runq(ErtsRunQueue *runq);
 void erts_sched_finish_poke(ErtsSchedulerSleepInfo *, erts_aint32_t);
 ERTS_GLB_INLINE void erts_sched_poke(ErtsSchedulerSleepInfo *ssi);
 void erts_aux_thread_poke(void);
+ERTS_GLB_INLINE Uint32 erts_sched_local_random_hash_64_to_32_shift(Uint64 key);
+ERTS_GLB_INLINE Uint32 erts_sched_local_random(Uint additional_seed);
+
 
 #if ERTS_GLB_INLINE_INCL_FUNC_DEF
 
@@ -2647,6 +2651,39 @@ erts_sched_poke(ErtsSchedulerSleepInfo *ssi)
 }
 
 
+/*
+ * Source: https://gist.github.com/badboy/6267743
+ *         http://web.archive.org/web/20071223173210/http://www.concentric.net/~Ttwang/tech/inthash.htm
+ */
+ERTS_GLB_INLINE
+Uint32 erts_sched_local_random_hash_64_to_32_shift(Uint64 key)
+{
+    key = (~key) + (key << 18); /* key = (key << 18) - key - 1; */
+    key = key ^ (key >> 31);
+    key = (key + (key << 2)) + (key << 4);
+    key = key ^ (key >> 11);
+    key = key + (key << 6);
+    key = key ^ (key >> 22);
+    return (Uint32) key;
+}
+
+/*
+ * This function attempts to return a random number based on the state
+ * of the scheduler, the current process and the additional_seed
+ * parameter.
+ */
+ERTS_GLB_INLINE
+Uint32 erts_sched_local_random(Uint additional_seed)
+{
+    ErtsSchedulerData *esdp = erts_get_scheduler_data();
+    Uint64 seed =
+        additional_seed +
+        esdp->reductions +
+        esdp->current_process->fcalls +
+        (((Uint64)esdp->no) << 32);
+    return erts_sched_local_random_hash_64_to_32_shift(seed);
+}
+
 #endif /* #if ERTS_GLB_INLINE_INCL_FUNC_DEF */