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)

CPM User at 07:03, 18 November 2015

2015-11-18T07:03:03Z

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

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

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

2010-12-17T08:46:34Z

added 16-bit routine with 'r' register

PulkoMandy at 14:09, 13 August 2006

2006-08-13T14:09:00Z

Octoate: Added RNG with lookup table

2006-08-09T17:11:46Z

Added RNG with lookup table

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>

@@ Line 88: / Line 88: @@
 <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
 </pre>

@@ 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>

@@ Line 1: / Line 1: @@
-== 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.
 '''Input:''' ''none''
@@ Line 18: / Line 37: @@
 </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''
@@ Line 35: / Line 54: @@
          add     a,l
          ld      l,a
-         jr      nc,.skip
+         jr      nc,skip
          inc     h
 .skip:  ld      a,(hl)
@@ Line 60: / Line 79: @@
 </pre>
-== 16-bit Random Number Generator ==
+=== 16-bit random number generator ===
 This algorithm uses a similar method, but returns much better results.
@@ Line 87: / Line 106: @@
 </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''
@@ Line 109: / Line 128: @@
 	ret
 </pre>
 [[Category:Programming]]

@@ Line 96: / Line 96: @@
 <pre>
-	ld a,r
+Rand16	ld a,r
 	ld h,a
-.rand8	ld b,a
+Rand8	ld b,a
 	add a,a
 	add a,a
 	add a,b
 	inc a
-	ld (rand8+1),a
+	ld (Rand8 + 1),a
 	ld l,a          ; HL now contains a random 16-bit number
 </pre>
 [[Category:Programming]]

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

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

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