MDEV-21256: Reduce the use of ut_rnd_gen_next_ulint()

ut_rnd_set_seed(): Unused function; remove.

ut_rnd_gen(): Renamed from page_cur_lcg_prng().

ut_rnd_current: The internal state of ut_rnd_gen().

page_cur_open_on_rnd_user_rec(): Replace linear search with
page_rec_get_nth().

1 files changed, 26 insertions, 28 deletions

diff --git a/storage/innobase/include/ut0rnd.h b/storage/innobase/include/ut0rnd.h
index b6d4d4abbd2..56b4a6159c1 100644
--- a/storage/innobase/include/ut0rnd.h
+++ b/storage/innobase/include/ut0rnd.h
@@ -1,6 +1,7 @@
 /*****************************************************************************
 
 Copyright (c) 1994, 2016, Oracle and/or its affiliates. All Rights Reserved.
+Copyright (c) 2019, MariaDB Corporation.
 
 This program is free software; you can redistribute it and/or modify it under
 the terms of the GNU General Public License as published by the Free Software
@@ -27,38 +28,35 @@ Created 1/20/1994 Heikki Tuuri
 #define ut0rnd_h
 
 #include "ut0byte.h"
+#include <my_sys.h>
 
 #ifndef UNIV_INNOCHECKSUM
-/** The 'character code' for end of field or string (used
-in folding records */
-#define UT_END_OF_FIELD		257
+/** Seed value of ut_rnd_gen() */
+extern uint64_t ut_rnd_current;
+
+/** @return a pseudo-random 64-bit number */
+inline uint64_t ut_rnd_gen()
+{
+	/*
+	This is a linear congruential pseudo random number generator.
+	The formula and the constants
+	being used are:
+	X[n+1] = (a * X[n] + c) mod m
+	where:
+	X[0] = my_interval_timer()
+	a = 1103515245 (3^5 * 5 * 7 * 129749)
+	c = 12345 (3 * 5 * 823)
+	m = 18446744073709551616 (1<<64), implicit */
+
+	if (UNIV_UNLIKELY(!ut_rnd_current)) {
+		ut_rnd_current = my_interval_timer();
+	}
+
+	ut_rnd_current = 1103515245 * ut_rnd_current + 12345;
+	return ut_rnd_current;
+}
 
 /********************************************************//**
-This is used to set the random number seed. */
-UNIV_INLINE
-void
-ut_rnd_set_seed(
-/*============*/
-	ulint	 seed);		 /*!< in: seed */
-/********************************************************//**
-The following function generates a series of 'random' ulint integers.
-@return the next 'random' number */
-UNIV_INLINE
-ulint
-ut_rnd_gen_next_ulint(
-/*==================*/
-	ulint	rnd);	/*!< in: the previous random number value */
-/*********************************************************//**
-The following function generates 'random' ulint integers which
-enumerate the value space (let there be N of them) of ulint integers
-in a pseudo-random fashion. Note that the same integer is repeated
-always after N calls to the generator.
-@return the 'random' number */
-UNIV_INLINE
-ulint
-ut_rnd_gen_ulint(void);
-/*==================*/
-/********************************************************//**
 Generates a random integer from a given interval.
 @return the 'random' number */
 UNIV_INLINE