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48 lines
875 B
C
48 lines
875 B
C
// http://www.6502.org/users/mycorner/6502/code/prng.html
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//; returns pseudo random 8 bit number in A. Affects A. (r_seed) is the
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//; byte from which the number is generated and MUST be initialised to a
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//; non zero value or this function will always return zero. Also r_seed
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//; must be in RAM, you can see why......
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//rand_8
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// LDA r_seed ; get seed
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// ASL ; shift byte
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// BCC no_eor ; branch if no carry
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//
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// EOR #$CF ; else EOR with $CF
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//no_eor
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// STA r_seed ; save number as next seed
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// RTS ; done
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//r_seed
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// .byte 1 ; prng seed byte, must not be zero
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#include <stdio.h>
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unsigned char r_seed=1;
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int rand8(void) {
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if (r_seed&0x80) {
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r_seed<<=1;
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r_seed^=0xcf;
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}
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else {
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r_seed<<=1;
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}
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return r_seed;
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}
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int main(int argc, char **argv) {
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int i,r;
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for(i=0;i<1024;i++) {
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r=rand8();
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printf("%d: %02X m%02X\n",i,r,r&0x1f);
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}
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return 0;
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}
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