Adventurer #13 31 марта 2002

Программирование

Exchange of experience - an unscientific Algorithm for Random Number (RND).

     (C) Research / Volgasoft


               Scientific RND


     In my esteemed journal Spectrum
Expert were laid out at least all the materials for self-writing
wire, and even the cast wire
engine ELITE. Now we learn how to generate pseudo-random 
numbers, and thus learn to write everything that happens inside 
the station (map of the galaxy and the names of the planets for 
example:). Enough will scrape a modest materialchik on

likeness of artificial intelligence, and anyone can write the 
elite for two months: 


     Main methods of generating random
There are two numbers (and finally can - one):

     1) the shift of floating point numbers
(Sometimes with the admixture of shifted copies);

     2) Papal method:) Tyk Now, consider the Pope's method:

N [i +1] = mod (A * N [i], Z); - where mod = Modulo
In other words: the next number = remainder of division of some 
constants A, multiplied by the previous number and the constant 
Z. That's it!


On the finger assembly:
constA EQU 137
; Z EQU 8
N EQU 3; seed


        LD IX, array; array address

        LD (IX), N

        LD DE, constA; constant A

        LD B, 32; how many numbers to generate
LL1

        LD L, (IX)

        LD H, 0

        PUSH DE

        CALL MUL_HL_DE; "A * N [i]"

        POP DE

        LD (IX +1), L; remainder of the division by 256, also 
known as the low byte 

        INC IX

        DJNZ LL1

; Ready


     The range of values ​​generated numbers
depends on the constants. In the example, Z = 256,
A = 137. The values ​​of Z - choose to taste
(Actually, in this example would not hurt
beginning to shift the result of multiplying
right by one bit, and then take the remainder). The values ​​of 
A are chosen so that the distribution was close to uniform. 
Usually taken  number (I forgot how their school was 
named - which are divided into themselves and one) such as 5, 
7.13, 17, 19, 23, etc. Make sure that there was no zeros, 
otherwise the generator will rise. As I have said that numbers 
were obtained not only odd or even - to play with the 
translations. 


     To generate numbers not only
arranged in a specified number of bits (8 -
1 .. 255, 7 - 1 .. 127) will have to ruin a few numbers, or use 
multiple generators, for example the numbers 1 .. 191:



        LD A, n1

        AND A, 1963

        LD C, A

        LD A, n2

        AND A, 127

        ADD A, C

        LD (RESULT), A


     But how to generate the names of the planets in the elite 
- everyone knows - we take, we make an array of syllables (two 
letters) and we start the generator - one number corresponds to 
one syllable, and rolls the two-letter planet, four, six:



     By the way, like algorithm is used in calculating the 
checksum, the including at the same VG93.



     Well that's all: How to tell you about the current
AI (or someone will tell in the pages
Adventurer 'a) from you with each of the elite
:))).