MDEV-21256: Simplify ut_rnd_interval()

ut_rnd_interval(): Remove the first parameter, which was mostly
passed as 0. Implement as a simple wrapper around ut_rnd_gen().
Trivially return 0 if the size of the interval is smaller than 2.

ut_rnd_ulint_counter, ut_rnd_gen_next_ulint(), ut_rnd_gen_ulint(): Remove.

storage/innobase/dict/dict0stats.cc

@@ -1747,7 +1747,7 @@ dict_stats_analyze_index_for_n_prefix(
 		ut_rnd_interval() to work with too big numbers since
 		ib_uint64_t could be bigger than ulint */
 		const ulint	rnd = ut_rnd_interval(
-			0, static_cast<ulint>(right - left));
+			static_cast<ulint>(right - left));
 
 		const ib_uint64_t	dive_below_idx
 			= boundaries->at(static_cast<unsigned>(left + rnd));

storage/innobase/include/ib0mutex.h

@@ -225,7 +225,7 @@ struct TTASFutexMutex {
 				return;
 			}
 
-			ut_delay(ut_rnd_interval(0, max_delay));
+			ut_delay(ut_rnd_interval(max_delay));
 		}
 
 		for (n_waits= 0;; n_waits++) {
@@ -362,7 +362,7 @@ struct TTASMutex {
 		uint32_t n_spins = 0;
 
 		while (!try_lock()) {
-			ut_delay(ut_rnd_interval(0, max_delay));
+			ut_delay(ut_rnd_interval(max_delay));
 			if (++n_spins == max_spins) {
 				os_thread_yield();
 				max_spins+= step;
@@ -516,7 +516,7 @@ struct TTASEventMutex {
 					sync_array_wait_event(sync_arr, cell);
 				}
 			} else {
-				ut_delay(ut_rnd_interval(0, max_delay));
+				ut_delay(ut_rnd_interval(max_delay));
 			}
 		}
 

storage/innobase/include/ut0rnd.h

@@ -56,15 +56,11 @@ inline uint64_t ut_rnd_gen()
 	return ut_rnd_current;
 }
 
-/********************************************************//**
-Generates a random integer from a given interval.
-@return the 'random' number */
-UNIV_INLINE
-ulint
-ut_rnd_interval(
-/*============*/
-	ulint	low,	/*!< in: low limit; can generate also this value */
-	ulint	high);	/*!< in: high limit; can generate also this value */
+/** @return a random number between 0 and n-1, inclusive */
+inline ulint ut_rnd_interval(ulint n)
+{
+  return n > 1 ? static_cast<ulint>(ut_rnd_gen() % n) : 0;
+}
 
 /*******************************************************//**
 The following function generates a hash value for a ulint integer

storage/innobase/include/ut0rnd.ic

@@ -29,87 +29,6 @@ Created 5/30/1994 Heikki Tuuri
 
 #ifndef UNIV_INNOCHECKSUM
 
-#define UT_RND1			151117737
-#define UT_RND2			119785373
-#define UT_RND3			 85689495
-#define UT_RND4			 76595339
-#define UT_SUM_RND2		 98781234
-#define UT_SUM_RND3		126792457
-#define UT_SUM_RND4		 63498502
-#define UT_XOR_RND1		187678878
-#define UT_XOR_RND2		143537923
-
-/** Seed value of ut_rnd_gen_ulint() */
-extern	ulint	 ut_rnd_ulint_counter;
-
-/********************************************************//**
-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 */
-{
-	ulint	n_bits;
-
-	n_bits = 8 * sizeof(ulint);
-
-	rnd = UT_RND2 * rnd + UT_SUM_RND3;
-	rnd = UT_XOR_RND1 ^ rnd;
-	rnd = (rnd << 20) + (rnd >> (n_bits - 20));
-	rnd = UT_RND3 * rnd + UT_SUM_RND4;
-	rnd = UT_XOR_RND2 ^ rnd;
-	rnd = (rnd << 20) + (rnd >> (n_bits - 20));
-	rnd = UT_RND1 * rnd + UT_SUM_RND2;
-
-	return(rnd);
-}
-
-/********************************************************//**
-The following function generates 'random' ulint integers which
-enumerate the value space of ulint integers in a pseudo random
-fashion. Note that the same integer is repeated always after
-2 to power 32 calls to the generator (if ulint is 32-bit).
-@return the 'random' number */
-UNIV_INLINE
-ulint
-ut_rnd_gen_ulint(void)
-/*==================*/
-{
-	ulint	rnd;
-
-	ut_rnd_ulint_counter = UT_RND1 * ut_rnd_ulint_counter + UT_RND2;
-
-	rnd = ut_rnd_gen_next_ulint(ut_rnd_ulint_counter);
-
-	return(rnd);
-}
-
-/********************************************************//**
-Generates a random integer from a given interval.
-@return the 'random' number */
-UNIV_INLINE
-ulint
-ut_rnd_interval(
-/*============*/
-	ulint	low,	/*!< in: low limit; can generate also this value */
-	ulint	high)	/*!< in: high limit; can generate also this value */
-{
-	ulint	rnd;
-
-	ut_ad(high >= low);
-
-	if (low == high) {
-
-		return(low);
-	}
-
-	rnd = ut_rnd_gen_ulint();
-
-	return(low + (rnd % (high - low)));
-}
-
 /*******************************************************//**
 The following function generates a hash value for a ulint integer
 to a hash table of size table_size, which should be a prime

storage/innobase/page/page0cur.cc

@@ -792,8 +792,7 @@ page_cur_open_on_rnd_user_rec(
 	}
 
 	cursor->rec = page_rec_get_nth(block->frame,
-				       static_cast<ulint>
-				       (ut_rnd_gen() % n_recs) + 1);
+				       ut_rnd_interval(n_recs) + 1);
 }
 
 /** Write a redo log record of inserting a record into an index page.

storage/innobase/sync/sync0rw.cc

@@ -299,7 +299,7 @@ rw_lock_s_lock_spin(
 	HMT_low();
 	while (i < srv_n_spin_wait_rounds && lock->lock_word <= 0) {
 		if (srv_spin_wait_delay) {
-			ut_delay(ut_rnd_interval(0, srv_spin_wait_delay));
+			ut_delay(ut_rnd_interval(srv_spin_wait_delay));
 		}
 
 		i++;
@@ -425,7 +425,7 @@ rw_lock_x_lock_wait_func(
 
 		HMT_low();
 		if (srv_spin_wait_delay) {
-			ut_delay(ut_rnd_interval(0, srv_spin_wait_delay));
+			ut_delay(ut_rnd_interval(srv_spin_wait_delay));
 		}
 
 		if (i < srv_n_spin_wait_rounds) {
@@ -684,8 +684,7 @@ rw_lock_x_lock_func(
 		       && lock->lock_word <= X_LOCK_HALF_DECR) {
 
 			if (srv_spin_wait_delay) {
-				ut_delay(ut_rnd_interval(
-						0, srv_spin_wait_delay));
+				ut_delay(ut_rnd_interval(srv_spin_wait_delay));
 			}
 
 			i++;
@@ -790,8 +789,7 @@ rw_lock_sx_lock_func(
 		       && lock->lock_word <= X_LOCK_HALF_DECR) {
 
 			if (srv_spin_wait_delay) {
-				ut_delay(ut_rnd_interval(
-						0, srv_spin_wait_delay));
+				ut_delay(ut_rnd_interval(srv_spin_wait_delay));
 			}
 
 			i++;

storage/innobase/ut/ut0rnd.cc

@@ -36,9 +36,6 @@ uint64_t ut_rnd_current;
 #define UT_RANDOM_3	1.0132677
 /*@}*/
 
-/** Seed value of ut_rnd_gen_ulint(). */
-ulint	ut_rnd_ulint_counter = 65654363;
-
 /***********************************************************//**
 Looks for a prime number slightly greater than the given argument.
 The prime is chosen so that it is not near any power of 2.