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().

5 files changed, 39 insertions, 105 deletions

diff --git a/storage/innobase/gis/gis0geo.cc b/storage/innobase/gis/gis0geo.cc
index fb55945549e..3a727185632 100644
--- a/storage/innobase/gis/gis0geo.cc
+++ b/storage/innobase/gis/gis0geo.cc
@@ -444,26 +444,6 @@ pick_seeds(
 	}
 }
 
-/*********************************************************//**
-Generates a random iboolean value.
-@return the random value */
-static
-ibool
-ut_rnd_gen_ibool(void)
-/*=================*/
-{
-	ulint    x;
-
-	x = ut_rnd_gen_ulint();
-
-	if (((x >> 20) + (x >> 15)) & 1) {
-
-		return(TRUE);
-	}
-
-	return(FALSE);
-}
-
 /*************************************************************//**
 Select next node and group where to add. */
 static
@@ -500,8 +480,7 @@ pick_next(
 			/* Introduce some randomness if the record
 			is identical */
 			if (diff == 0) {
-				diff = static_cast<double>(
-					ut_rnd_gen_ibool());
+				diff = static_cast<double>(ut_rnd_gen() & 1);
 			}
 
 			*n_group = 1 + (diff > 0);
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
diff --git a/storage/innobase/include/ut0rnd.ic b/storage/innobase/include/ut0rnd.ic
index 0003c42baad..8b7ea5fe1e4 100644
--- a/storage/innobase/include/ut0rnd.ic
+++ b/storage/innobase/include/ut0rnd.ic
@@ -1,7 +1,7 @@
 /*****************************************************************************
 
 Copyright (c) 1994, 2016, Oracle and/or its affiliates. All Rights Reserved.
-Copyright (c) 2017, MariaDB Corporation.
+Copyright (c) 2017, 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
@@ -43,17 +43,6 @@ Created 5/30/1994 Heikki Tuuri
 extern	ulint	 ut_rnd_ulint_counter;
 
 /********************************************************//**
-This is used to set the random number seed. */
-UNIV_INLINE
-void
-ut_rnd_set_seed(
-/*============*/
-	ulint	 seed)		 /*!< in: seed */
-{
-	ut_rnd_ulint_counter = seed;
-}
-
-/********************************************************//**
 The following function generates a series of 'random' ulint integers.
 @return the next 'random' number */
 UNIV_INLINE
diff --git a/storage/innobase/page/page0cur.cc b/storage/innobase/page/page0cur.cc
index b4ec3e6dcdf..a5a8c6c3d1e 100644
--- a/storage/innobase/page/page0cur.cc
+++ b/storage/innobase/page/page0cur.cc
@@ -35,38 +35,6 @@ Created 10/4/1994 Heikki Tuuri
 
 #include <algorithm>
 
-/*******************************************************************//**
-This is a linear congruential generator PRNG. Returns a pseudo random
-number between 0 and 2^64-1 inclusive. 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 (2^64)
-
-@return number between 0 and 2^64-1 */
-static
-ib_uint64_t
-page_cur_lcg_prng(void)
-/*===================*/
-{
-#define LCG_a	1103515245
-#define LCG_c	12345
-	static uint64_t	lcg_current;
-
-	if (!lcg_current) {
-		lcg_current = my_interval_timer();
-	}
-
-	/* no need to "% 2^64" explicitly because lcg_current is
-	64 bit and this will be done anyway */
-	lcg_current = LCG_a * lcg_current + LCG_c;
-
-	return(lcg_current);
-}
-
 #ifdef BTR_CUR_HASH_ADAPT
 # ifdef UNIV_SEARCH_PERF_STAT
 static ulint	page_cur_short_succ;
@@ -814,8 +782,7 @@ page_cur_open_on_rnd_user_rec(
 	buf_block_t*	block,	/*!< in: page */
 	page_cur_t*	cursor)	/*!< out: page cursor */
 {
-	ulint	rnd;
-	ulint	n_recs = page_get_n_recs(buf_block_get_frame(block));
+	const ulint	n_recs = page_get_n_recs(block->frame);
 
 	page_cur_set_before_first(block, cursor);
 
@@ -824,11 +791,9 @@ page_cur_open_on_rnd_user_rec(
 		return;
 	}
 
-	rnd = (ulint) (page_cur_lcg_prng() % n_recs);
-
-	do {
-		page_cur_move_to_next(cursor);
-	} while (rnd--);
+	cursor->rec = page_rec_get_nth(block->frame,
+				       static_cast<ulint>
+				       (ut_rnd_gen() % n_recs) + 1);
 }
 
 /** Write a redo log record of inserting a record into an index page.
@@ -2426,18 +2391,17 @@ page_cur_delete_rec(
 #ifdef UNIV_COMPILE_TEST_FUNCS
 
 /*******************************************************************//**
-Print the first n numbers, generated by page_cur_lcg_prng() to make sure
+Print the first n numbers, generated by ut_rnd_gen() to make sure
 (visually) that it works properly. */
 void
-test_page_cur_lcg_prng(
-/*===================*/
+test_ut_rnd_gen(
 	int	n)	/*!< in: print first n numbers */
 {
 	int			i;
 	unsigned long long	rnd;
 
 	for (i = 0; i < n; i++) {
-		rnd = page_cur_lcg_prng();
+		rnd = ut_rnd_gen();
 		printf("%llu\t%%2=%llu %%3=%llu %%5=%llu %%7=%llu %%11=%llu\n",
 		       rnd,
 		       rnd % 2,
diff --git a/storage/innobase/ut/ut0rnd.cc b/storage/innobase/ut/ut0rnd.cc
index 3c1e51536a1..dcf43b9d7e1 100644
--- a/storage/innobase/ut/ut0rnd.cc
+++ b/storage/innobase/ut/ut0rnd.cc
@@ -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
@@ -25,6 +26,9 @@ Created 5/11/1994 Heikki Tuuri
 
 #include "ut0rnd.h"
 
+/** Seed value of ut_rnd_gen() */
+uint64_t ut_rnd_current;
+
 /** These random numbers are used in ut_find_prime */
 /*@{*/
 #define	UT_RANDOM_1	1.0412321