Programming:Random Number Generator - Revision history

CPM User: /* 8-bit random number generator using Refresh Register (R) */

2016-01-08T21:11:54Z

8-bit random number generator using Refresh Register (R)

← Older revision		Revision as of 21:11, 8 January 2016
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	<pre>		<pre>
	~~.rnd~~		;-----> Generate a random number
	ld a,r		; ouput a=answer 0<=a<=255
	ld b,a		ld hl,(seed_ion)
	ld a,~~(seed)~~		ld a,r
	xor b		ld d,a
	add a		ld e,a
	xor b		add hl,de
	ld (~~seed~~),a		xor l
	ret		add a
	.~~seed db 0~~		xor h
			ld l,a
			ld (seed_ion),hl
			ret
			seed_ion: .dw 0x0
	</pre>		</pre>

CPM User at 07:03, 18 November 2015

2015-11-18T07:03:03Z

@@ Line 77: / Line 77: @@
          db      &70,&27,&F7,&1F,&BE,&12,&B6,&50,&BC,&4D,&28,&C8,&84,&30,&A5,&4C
          db      &AB,&E9,&8E,&E8,&7E,&C4,&89,&8B,&0B,&24,&85,&3E,&38,&04,&D2,&90
 </pre>

Nich: Added section on generating random numbers from BASIC, and reorganised and renamed other headings

2010-12-23T11:29:43Z

Added section on generating random numbers from BASIC, and reorganised and renamed other headings

← Older revision		Revision as of 11:29, 23 December 2010
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	== ~~8-bit Random Number Generator~~ ==		== BASIC ==

	This is a very simple generator. ~~It's~~ function is x[i + 1] = (5 * x[i] + 1) mod 256. The only advantage is the small size and ~~it's~~ simplicity.		The BASIC command <tt>RANDOMIZE TIME</tt> can be used to generate random numbers, using the value of the <tt>TIME</tt> variable as a seed. The <tt>TIME</tt> variable is incremented every 1/300th of a second, so it is highly unlikely that the same set of numbers will be generated each time the BASIC program is run.

			However, after about five or six numbers are obtained using the <tt>RND</tt> command, the randomness of the numbers decreases dramatically. The listing below demonstrates this problem:

			<pre>10 MODE 2
			20 FOR a=1 TO 23
			30 RANDOMIZE TIME
			40 FOR b=1 TO 25
			50 PRINT USING("## ");INT(RND*100);
			60 NEXT b
			70 PRINT
			80 NEXT a</pre>

			This problem can be overcome by using the commands <tt>RANDOMIZE TIME:RANDOMIZE RND</tt> instead. This re-initialises the random number seed and greatly improves the randomness of the numbers that are obtained using the <tt>RND</tt> command.

			== Machine code ==

			=== 8-bit random number generator ===

			This is a very simple generator. Its function is x[i + 1] = (5 * x[i] + 1) mod 256. The only advantage is the small size and its simplicity.

	'''Input:''' ''none''		'''Input:''' ''none''
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	</pre>		</pre>

	== 8-bit ~~Random Number Generator -~~ lookup table based ==		=== 8-bit random number generator (lookup table based) ===

	To use this routine you need to define 1 ~~Byte~~ of RAM for the ''RandomPtr''.		To use this routine you need to define 1 byte of RAM for the ''RandomPtr''.

	'''Input:''' ''none''		'''Input:''' ''none''
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	add a,l		add a,l
	ld l,a		ld l,a
	jr nc,.skip		jr nc,skip
	inc h		inc h
	.skip: ld a,(hl)		.skip: ld a,(hl)
Line 60:		Line 79:
	</pre>		</pre>

	== 16-bit ~~Random Number Generator~~ ==		=== 16-bit random number generator ===

	This algorithm uses a similar method, but returns much better results.		This algorithm uses a similar method, but returns much better results.
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	</pre>		</pre>

	== 16-bit ~~Random Number Generator~~ using ~~'r'~~ register ==		=== 16-bit random number generator using the R register ===

	A pseudo random generator using the ~~'r'~~ register for the first byte of the random number. It then uses this number as a seed to feed the 8-bit random number generator to generate the other byte of the random value.		A pseudo random generator using the R register for the first byte of the random number. It then uses this number as a seed to feed the 8-bit random number generator to generate the other byte of the random value.

	'''Input:''' ''none''		'''Input:''' ''none''
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	ret		ret
	</pre>		</pre>

	[[Category:Programming]]		[[Category:Programming]]

Octoate: /* 16-bit Random Number Generator using 'r' register */ changed labels, added ret

2010-12-17T08:47:51Z

16-bit Random Number Generator using 'r' register: changed labels, added ret

← Older revision		Revision as of 08:47, 17 December 2010
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	<pre>		<pre>
	ld a,r		Rand16 ld a,r
	ld h,a		ld h,a

	~~.rand8~~ ld b,a		Rand8 ld b,a
	add a,a		add a,a
	add a,a		add a,a
	add a,b		add a,b
	inc a		inc a
	ld (~~rand8~~+1),a		ld (Rand8 + 1),a

	ld l,a ; HL now contains a random 16-bit number		ld l,a ; HL now contains a random 16-bit number
			ret
	</pre>		</pre>
	[[Category:Programming]]		[[Category:Programming]]

Octoate: added 16-bit routine with 'r' register

2010-12-17T08:46:34Z

added 16-bit routine with 'r' register

@@ Line 85: / Line 85: @@
 Rand	ld	(Rand16+1),hl
 	ret
 </pre>
 [[Category:Programming]]

PulkoMandy at 14:09, 13 August 2006

2006-08-13T14:09:00Z

← Older revision		Revision as of 14:09, 13 August 2006
Line 86:		Line 86:
	ret		ret
	</pre>		</pre>
			[[Category:Programming]]

Octoate: Added RNG with lookup table

2006-08-09T17:11:46Z

Added RNG with lookup table

@@ Line 16: / Line 16: @@
 	ld	(Rand8+1),a
 	ret
 </pre>

Octoate: Initial page

2006-08-06T19:11:37Z

Initial page

New page

== 8-bit Random Number Generator ==

This is a very simple generator. It's function is x[i + 1] = (5 * x[i] + 1) mod 256. The only advantage is the small size and it's simplicity.

'''Input:''' ''none''

'''Output:''' A = ''a pseudo random number, period 256''

<pre>
Rand8 ld a,Seed ; Seed is usually 0
ld b,a
add a,a
add a,a
add a,b
inc a ; another possibility is ADD A,7
ld (Rand8+1),a
ret
</pre>

== 16-bit Random Number Generator ==

This algorithm uses a similar method, but returns much better results.

'''Input:''' ''none''

'''Output:''' A = ''a pseudo random number, period 65536''

<pre>
Rand16 ld de,Seed ; Seed is usually 0
ld a,d
ld h,e
ld l,253
or a
sbc hl,de
sbc a,0
sbc hl,de
ld d,0
sbc a,d
ld e,a
sbc hl,de
jr nc,Rand
inc hl
Rand ld (Rand16+1),hl
ret
</pre>