8-bit PRNG

// rngtest < ./rand
// ./rand | dieharder -B -g 200 -a
#include <stdio.h>
#include <stdlib.h>
#include <stdint.h>
#include <math.h>


int main() {

	//starting number and table indices
	uint8_t num = 43;
	uint8_t a=131;
	uint8_t b=73;

	//bit width
	const uint8_t bw = sizeof(num)*8;

	//tables of random numbers
    uint8_t atab[] = {
		2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43, 47, 53
	};

    uint8_t btab[] = {
		59, 61, 67, 71, 73, 79, 83, 89, 97, 101, 103, 107, 109, 113, 127, 131
	};

	//number of elements in the tables (must be power of two that we can avoid expensive modulus)
	const uint8_t elems=sizeof(atab)/sizeof(atab[0]);

	while(1){
		a = (a+num&(elems-1)) & (elems-1); //use 'num' to set a index
		b = (b+1			) & (elems-1); //b index increments by 1 and loops

		//swap elements
		uint8_t buf = atab[a];
		atab[a]=btab[b]+num; //add num for additional mixing
		btab[b]=buf;

		uint8_t shift = a&(bw-1); //right shift amount

		num = (num>>shift) | (num<<(bw-shift)); //ror
		num = num ^ atab[a] + btab[b]; //mixing

		fwrite(&num, sizeof(uint8_t), 1, stdout); //write
	}

    return 0;

}