#include <stdio.h>
#include <string.h>
 
bool neighbours(double a, double b)
{
    unsigned long long x;
    unsigned long long y;
    // not portable, yadda yadda yadda
    memcpy(&x, &a, 8);
    memcpy(&y, &b, 8);
    printf("distance: %llu\n", x - y);
    // no more than 1 apart?
    return x - y + 1 <= 2;
}
 
const char * notstr[] = {"not ", ""};
 
void test(double a, double b)
{
    printf("%.17f and\n%.17f are %sneighbours.\n\n", a, b, notstr[neighbours(a, b)]);
}
 
const unsigned long long EVENS = 9007199254740992;
 
int main()
{
    test(0.1 + 0.2, 0.3);
    test(0.5, 0.49999999999);
 
    test(EVENS + 1, EVENS);
    test(EVENS + 2, EVENS);
    test(EVENS + 3, EVENS);
    test(EVENS + 4, EVENS);
    test(EVENS + 5, EVENS);
}
 

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