mrfloat.c

#include <stdio.h>
#include <string.h>
#include <softfloat.h>

const double mul = 1.0000001;

double doit(double in, long unsigned iteration) {
        #pragma nounroll
        for(long unsigned u = 0; u < iteration; ++u)
                in *= mul;
        return in;
}

double doit_soft(double in, long unsigned iteration) {
        float64_t x;
        float64_t m;
        memcpy((char*)&x, (char*)&in, 8);
        memcpy((char*)&m, (char*)&mul, 8);
        #pragma nounroll
        for(long unsigned u = 0; u < iteration; ++u)
                x = f64_mul(x, m);
        double ret;
        memcpy((char*)&ret, (char*)&x, 8);
        return ret;
}

int main() {
        double in = 4;
        unsigned long it = 1000000000;
        unsigned long long start, end;

        start = __builtin_readcyclecounter();
        double out = doit(in, it);
        end = __builtin_readcyclecounter();
        printf("%lf  --  %llu\n", out, end-start);

        start = __builtin_readcyclecounter();
        double softout = doit_soft(in, it);
        end = __builtin_readcyclecounter();
        printf("%lf  --  %llu\n", out, end-start);
}