Decode a hex representation into a float

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

void hex_2_f(char* s)
{
    int i;

    long tmp = strtol(s, NULL, 16);

    printf("String: %s, Parsed to: %x\n", s, tmp);

    int sign = tmp >> 31;
    int exp = ((tmp >> 23) & 0xFF);
    int base = tmp & 0x7fffff;


    float result = (1 - 2*sign)*(1 + (base*(powf(2,-23))))*(powf(2,exp-127));
    printf("RESULT:: %f\n", result);

}

int main(int argc, char* argv[])
{
    float f;
    if (argc < 2)
    {   printf("usage: %s [hex val to convert to float]\n", argv[0]);
    }
    else
    {   hex_2_f(argv[1]);
    }
}

Round a FP number to an epsilon

float hack(float in, float epsilon)
{
    float in_p = in;

    int steps = (int)log10(in / epsilon) + 1;
    int start = (int)log10(in) ;

    if (in < 1) start--;

    float ans = 0.0;

    while (true)
    {
        int tmp = (int)(in_p / pow10(start));
        ans  += tmp*pow10(start);
        in_p -= tmp*pow10(start);
        start--;
        steps--;
        if (!steps) break;
    }
    return ans;
}

int main(void)
{
    printf("I GET %e\n", hack(789.145, .1));
    return 1;
}

-- MattWalsh - 06 Aug 2009