commit 62fb0ae: [Minor] Use slightly better fast PRNGs

[Vsevolod Stakhov]

Author: Vsevolod Stakhov
Date: 2019-10-31 09:25:09 +0000
URL: https://github.com/rspamd/rspamd/commit/62fb0aeba5648ab32d4669ed9b9960f3304b6656 (HEAD -> master)

[Minor] Use slightly better fast PRNGs

---
 src/libutil/util.c | 52 +++++++++++++++++++++++++++++++++++-----------------
 src/libutil/util.h |  2 +-
 src/lua/lua_task.c |  4 ++--
 3 files changed, 38 insertions(+), 20 deletions(-)

diff --git a/src/libutil/util.c b/src/libutil/util.c
index 5fe8301fc..5ada3a27e 100644
--- a/src/libutil/util.c
+++ b/src/libutil/util.c
@@ -2638,7 +2638,7 @@ rspamd_random_double (void)
 }
 
 
-static guint64 xorshifto_seed[2];
+static guint64 xorshifto_seed[4];
 
 static inline guint64
 xoroshiro_rotl (const guint64 x, int k) {
@@ -2651,34 +2651,52 @@ rspamd_random_double_fast (void)
 	return rspamd_random_double_fast_seed (xorshifto_seed);
 }
 
-gdouble
-rspamd_random_double_fast_seed (guint64 seed[2])
+/* xoshiro256+ */
+inline gdouble
+rspamd_random_double_fast_seed (guint64 seed[4])
 {
-	const guint64 s0 = seed[0];
-	guint64 s1 = seed[1];
-	const guint64 result = s0 + s1;
+	const uint64_t result = seed[0] + seed[3];
+
+	const uint64_t t = seed[1] << 17;
+
+	seed[2] ^= seed[0];
+	seed[3] ^= seed[1];
+	seed[1] ^= seed[2];
+	seed[0] ^= seed[3];
+
+	seed[2] ^= t;
 
-	s1 ^= s0;
-	seed[0] = xoroshiro_rotl(s0, 55) ^ s1 ^ (s1 << 14);
-	seed[1] = xoroshiro_rotl (s1, 36);
+	seed[3] = xoroshiro_rotl (seed[3], 45);
 
 	return rspamd_double_from_int64 (result);
 }
 
-guint64
-rspamd_random_uint64_fast (void)
+/* xoroshiro256** */
+static inline guint64
+rspamd_random_uint64_fast_seed (guint64 seed[4])
 {
-	const guint64 s0 = xorshifto_seed[0];
-	guint64 s1 = xorshifto_seed[1];
-	const guint64 result = s0 + s1;
+	const uint64_t result = xoroshiro_rotl (seed[1] * 5, 7) * 9;
+
+	const uint64_t t = seed[1] << 17;
 
-	s1 ^= s0;
-	xorshifto_seed[0] = xoroshiro_rotl(s0, 55) ^ s1 ^ (s1 << 14);
-	xorshifto_seed[1] = xoroshiro_rotl (s1, 36);
+	seed[2] ^= seed[0];
+	seed[3] ^= seed[1];
+	seed[1] ^= seed[2];
+	seed[0] ^= seed[3];
+
+	seed[2] ^= t;
+
+	seed[3] = xoroshiro_rotl (seed[3], 45);
 
 	return result;
 }
 
+guint64
+rspamd_random_uint64_fast (void)
+{
+	return rspamd_random_uint64_fast_seed (xorshifto_seed);
+}
+
 void
 rspamd_random_seed_fast (void)
 {
diff --git a/src/libutil/util.h b/src/libutil/util.h
index c482a2d9f..d6f023205 100644
--- a/src/libutil/util.h
+++ b/src/libutil/util.h
@@ -424,7 +424,7 @@ gdouble rspamd_random_double (void);
  * @return
  */
 gdouble rspamd_random_double_fast (void);
-gdouble rspamd_random_double_fast_seed (guint64 seed[2]);
+gdouble rspamd_random_double_fast_seed (guint64 seed[4]);
 guint64 rspamd_random_uint64_fast (void);
 
 /**
diff --git a/src/lua/lua_task.c b/src/lua/lua_task.c
index 263aa83fa..e59bd3685 100644
--- a/src/lua/lua_task.c
+++ b/src/lua/lua_task.c
@@ -2118,7 +2118,7 @@ struct lua_tree_cb_data {
 	gint mask;
 	gint need_images;
 	gdouble skip_prob;
-	guint64 xoroshiro_state[2];
+	guint64 xoroshiro_state[4];
 };
 
 static void
@@ -2161,7 +2161,7 @@ lua_task_urls_adjust_skip_prob (struct rspamd_task *task,
 		memcpy (&cb->xoroshiro_state[0], &task->task_timestamp,
 				MIN (sizeof (cb->xoroshiro_state[0]), sizeof (task->task_timestamp)));
 		memcpy (&cb->xoroshiro_state[1], MESSAGE_FIELD (task, digest),
-				sizeof (cb->xoroshiro_state[1]));
+				sizeof (cb->xoroshiro_state[1]) * 3);
 		sz = max_urls;
 	}