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@unprovable unprovable/test.c
Created Nov 18, 2017

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#include <stdlib.h>
#include <stdio.h>
static int do_rand(unsigned long *ctx)
{
/*
* Compute x = (7^5 * x) mod (2^31 - 1)
* wihout overflowing 31 bits:
* (2^31 - 1) = 127773 * (7^5) + 2836
* From "Random number generators: good ones are hard to find",
* Park and Miller, Communications of the ACM, vol. 31, no. 10,
* October 1988, p. 1195.
*/
long hi, lo, x;
x = *ctx;
/* Can't be initialized with 0, so use another value. */
if (x == 0)
x = 123459876L;
hi = x / 127773L;
lo = x % 127773L;
x = 16807L * lo - 2836L * hi;
if (x < 0)
x += 0x7fffffffL;
return ((*ctx = x) % ((unsigned long)RAND_MAX + 1));
}
static unsigned long next = 1;
int rand(void)
{
return do_rand(&next);
}
void srand(unsigned int seed)
{
next = seed;
}
int main(int argc, char **argv)
{
char *p;
long conv = strtol(argv[1], &p, 10);
srand(conv); // seed with input
unsigned long start = rand(); // get starting number
if ((start & 0xffff) == 0){
printf("%04x\n", start);
}
long unsigned int t;
//for (int i=0; i<8000000; i++) {
while(1){
t = rand();
if (t == start){
printf("We are done!");
return 0;
}
if ((t & 0xffff) == 0){
printf("%04x\n", t);
}
}
}
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