roundish.cc

#include <assert.h>
#include <stdio.h>

int main() {
    double from = (1LL << 52), to = from + 2;
    long long bucket[3] = { 0 };
    int i;

    for (i = 0; i < 1000000; i++) {
        double r = from + (to - from) * (i / 1000000.);
        unsigned int b = (int)(r - from);
        assert(b < 3);
        bucket[b]++;
    }
    for(i = 0; i < 3; i++ ) {
        printf("%lld\n", bucket[i]);
    }
    return 0;
}

roundish.txt

$ g++ roundish.cc && ./a.out
250001
499999
250000