The Generate Random Number command allows you to create random
numbers. This is a useful function for several types of
applications:
- Simulations
- Creating test data
- Creating a relative record number (synonyms will exist)
- Performance testing
- Playing games (Spin the wheel, roll the dice etc.)
See also the GENUNQNBR tool for generating unique numbers.
A typical command would be entered as:
GENRANNBR RANNBR(&RANNBR) LOVAL(1) HIVAL(1000)
This would return a random number between 1 and 1000.
There are two ways to use the command:
** The default is to use the current time as a beginning value.
Each time you use the command, you will receive a different
random number. If you request multiple uses of the command,
the numbers will vary. This is the technique to use when you
want random data.
** A starting value may be specified to be used instead of the
beginning time. This allows you to receive the same number or
set of numbers each time you make a request. A starting value
would normally be used when you are doing performance testing
and want the same test values for repeated tests or when you
are generating a relative record number based on a key.
A command interface is provided or the CPP can be called directly
with a parameter list.
The command returns a value so therefore it can only be used in a CL
program.
Randomizing results
-------------------
The randomizing technique is fairly good. It will spread the values
over the range available. If a wide range exists and the amount of
numbers generated is not great, there will be minimal duplicates.
With a small range of possible values (e.g. 2-10), the randomization
is still reasonably good.
A perfect randomization is not achieved (nor is it achieved in real
life).
If you are interested in testing the results of the randomization, be
sure to run the same test multiple times (assuming a 0 start value).
The results will vary each time you run a test in the same manner it
varies in real life.
Using relative record numbers
-----------------------------
Generating a relative record number from a key value is a typical use
of the need for a random number. The use of relative record numbers
can be a performance advantage in that it does not require a search
of an index. However, you normally must provide a larger space than
is necessary and handle the synonyms (a synonym is where two keys
would generate the same random number).
The algorithm used by the tool is not very efficient as it uses a
combination of multiply and divide. This can use considerable CPU
resources.
Accessing randomly by relative record number may not be significantly
more efficient than keyed processing. The major potential gain is
the avoidance of paging in the index pages. In a system with
sufficient memory, the index pages will more likely be in memory.
The most likely place for a gain is when you are doing interactive
work.
Assume you have 1000 records and speed of access is essential. You
could create a data file that was initialized so there was room for
10,000 records. The larger the space you create the less possibility
there will be of synonyms. With a 10 to 1 ratio (10,000 slots to be
filled by 1,000 records), you would typically get about 95% unique
requests using the GENRANNBR command (assuming your starting values
were unique). This means that about 5% of the time you would have to
handle a synonym.
A typical means of handling a synonym would be to look in the next
relative record number slot to see if the key really matches.
You may want to try some different starting values with your data to
determine the best one to use (the one which normally gives you the
most unique values as well as spreading the numbers).
Parameter list
--------------
You may call the TAANBRAR command processing program directly with a
HLL program. The parameter list is as follows:
RANNBR *DEC LEN(9 0) The number to be returned
LOVAL *DEC LEN(9 0) The lowest value to be returned
HIVAL *DEC LEN(9 0) The highest value to be returned
PGMEND *CHAR LEN(4) *YES/*NO value for setting LR
STRVAL *DEC LEN(9 0) 0 = Random start, n = fxd str
The following code is in the proper format to be copied into an RPG
program. Use CPYTAA TAAARCMBR(GENRANNBR) to copy this documentation
source to the QATTINFO file in TAATOOL.
C Z-ADD1 LOVAL Low value
C Z-ADD50000 HIVAL High value
C Z-ADD0 STRVAL Start value
C MOVE '*NO ' PGMEND Program end
C CALL 'TAANBRAR' Call pgm
C PARM RANNBR 90 Random nbr
C PARM LOVAL 90 Low value
C PARM HIVAL 90 High value
C PARM PGMEND 4 Program end
C PARM STRVAL 90 Start value
Sample program to simulate flipping a coin for heads or tails
-------------------------------------------------------------
The following program shows how the GENRANNBR command can be used to
simulate flipping a coin.
PGM /* FLIP program for simulating coin toss */
DCL &RANNBR *DEC LEN(9 0)
DCL &FLIP *CHAR LEN(10)
GENRANNBR RANNBR(&RANNBR) LOVAL(1) HIVAL(2) PGMEND(*YES)
IF (&RANNBR *EQ 1) CHGVAR &FLIP 'HEADS'
IF (&RANNBR *EQ 2) CHGVAR &FLIP 'TAILS'
SNDPGMMSG MSG(&FLIP)
ENDPGM
Sample program to simulate tossing two dice
-------------------------------------------
PGM /* ROLL program to simulate roll of 2 dice */
DCL &RANNBR *DEC LEN(9 0)
DCL &TOTAL *DEC LEN(9 0)
DCL &ROLLAMT *CHAR LEN(22)
GENRANNBR RANNBR(&RANNBR) LOVAL(1) HIVAL(6)
CHGVAR &TOTAL (&TOTAL + &RANNBR)
GENRANNBR RANNBR(&RANNBR) LOVAL(1) HIVAL(6) PGMEND(*YES)
CHGVAR &TOTAL (&TOTAL + &RANNBR)
EDTVAR CHROUT(&ROLLAMT) NUMINP(&TOTAL)
SNDPGMMSG MSG(&ROLLAMT)
ENDPGM
Command parameters *CMD
------------------
RANNBR The random number to be returned. It must be
defined as a 9 digit field with 0 decimals.
LOVAL The lowest number you want returned. It must be
defined as *DEC LEN(9 0). It cannot be less than 0.
HIVAL The highest number you want returned. It must be
defined as *DEC LEN(9 0). It cannot be less than or
equal to LOVAL.
PGMEND A *YES/*NO value that determines whether the command
processing program should end (set LR on). The
default is *NO. If you are going to request a
series of numbers, you would say *NO until the last
request.
STRVAL Starting value. A *DEC LEN(9 0) value. A 0 entry
means that the function should pick a random value
to begin with. The current time in 9 digits is used
and is added to the YYMMDD value in a scrambled
fashion. With a 0 value, you would receive a
different set of values each time you made the same
request.
A specific value requests the same number or set of
numbers each time you make a request. A specific
value would normally be used when you are doing
performance testing or generating a relative record
number. Any 9 digit value may be entered.
Restrictions
------------
None.
Prerequisites
-------------
None.
Implementation
--------------
None, the tool is ready to use.
Objects used by the tool
------------------------
Object Type Attribute Src member Src file
------ ----- --------- ---------- -----------
GENRANNBR *CMD TAANBRA QATTCMD
TAANBRAR *PGM RPG TAANBRAR QATTRPG
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