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== 8-bit Random Number Generator BASIC ==

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 220 FOR a=1 TO 2330 RANDOMIZE TIME40 FOR b=1 TO 2550 PRINT USING("## ");INT(RND*100);60 NEXT b70 PRINT80 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. It's Its function is x[i + 1] = (5 * x[i] + 1) mod 256. The only advantage is the small size and it's its simplicity.

=== 8-bit random number generator (lookup table based) === To use this routine you need to define 1 byte of RAM for the ''RandomPtr''. '''Input:''' ''none'' '''Output:''' A = ''a pseudo random number, period 256'' <pre>RandomNumber: push hl ld a,(RandomPtr) inc a ld (RandomPtr),a ld hl,RandTable add a,l ld l,a jr nc,skip inc h.skip: ld a,(hl) pop hl ret RandTable: db &3B,&02,&B7,&6B,&08,&74,&1A,&5D,&21,&99,&95,&66,&D5,&59,&05,&42 db &F8,&03,&0F,&53,&7D,&8F,&57,&FB,&48,&26,&F2,&4A,&3D,&E4,&1D,&D9 db &9D,&DC,&2F,&F5,&92,&5C,&CC,&00,&73,&15,&BF,&B1,&BB,&EB,&9E,&2E db &32,&FC,&4B,&CD,&A7,&E6,&C2,&10,&11,&80,&52,&B2,&DA,&77,&4F,&EC db &13,&54,&64,&ED,&94,&8C,&C6,&9A,&19,&9F,&75,&FA,&AA,&8D,&FE,&91 db &01,&23,&07,&C1,&40,&18,&51,&76,&3C,&BD,&2A,&88,&2D,&F1,&8A,&72 db &F6,&98,&35,&97,&68,&93,&B3,&0C,&82,&4E,&CB,&39,&D8,&5F,&C7,&D4 db &CE,&AE,&6D,&A3,&7C,&6A,&B8,&A6,&6F,&5E,&E5,&1B,&F4,&B5,&3A,&14 db &78,&FD,&D0,&7A,&47,&2C,&A8,&1E,&EA,&2B,&9C,&86,&83,&E1,&7B,&71 db &F0,&FF,&D1,&C3,&DB,&0E,&46,&1C,&C9,&16,&61,&55,&AD,&36,&81,&F3 db &DF,&43,&C5,&B4,&AF,&79,&7F,&AC,&F9,&37,&E7,&0A,&22,&D3,&A0,&5A db &06,&17,&EF,&67,&60,&87,&20,&56,&45,&D7,&6E,&58,&A9,&B0,&62,&BA db &E3,&0D,&25,&09,&DE,&44,&49,&69,&9B,&65,&B9,&E0,&41,&A4,&6C,&CF db &A1,&31,&D6,&29,&A2,&3F,&E2,&96,&34,&EE,&DD,&C0,&CA,&63,&33,&5B 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> === 8-bit random number generator using Refresh Register (R) === Code courtesy from Singaja, this seems to produce a more random effect. '''Input:''' ''none'' '''Output:''' seed = ''a pseudo random number, period 256'' <pre> ;-----> Generate a random number ; ouput a=answer 0<=a<=255 ld hl,(seed_ion) ld a,r ld d,a ld e,a add hl,de xor l add a xor h ld l,a ld (seed_ion),hl ret seed_ion: .dw 0x0</pre> === 16-bit Random Number Generator random number generator ===