convertfloat.cpp

#include <iostream>
#include <cmath>

using namespace std;

float F16ConvertToF32(uint16_t f16)
{
    float f32 = 0;
    unsigned sign = (f16 & 0x8000) >> 15;       //extract out the sign
    unsigned exponent = ((f16 & 0x7C00) >> 10); //extract out the exponent
    float fraction = (f16 & 0x03ff) / 1024.0;   //extract out the fraction
    //check for inf & NaN, 0x7F800000 = +inf 0xFF800000 = -inf
    if (exponent == 0x1f)
    {
        if (fraction == 0)
        {
            int positveInf = 0x7f800000;
            int negativeInf = 0xff800000;
            return (sign == 0) ? *(float *)&positveInf : *(float *)&negativeInf;
        }
        else
        {
            return 0.0 / 0.0; //use 0.0 to generate NaN
        }
    }
    //check for 0 or subnormal
    if (exponent == 0)
    {
        if (fraction == 0)
        { // if it is 0
            if (sign == 1)
                return -0.0;
            return 0.0; // use 0.0 to return a zero in float
        }
        else
        {
            f32 = fraction * pow(2.0, -14.0);
            if (sign == 1)
                f32 *= -1.0;
            return f32;
        }
    }
    //the number is not a NaN or 0 or subnormal
    f32 = (fraction + 1.0) * pow(2.0, ((int)exponent - 15));
    if (sign == 1)
        f32 *= -1.0;
    return f32;
}

int main(int argc, char **argv)
{
    char *pCh;
    unsigned long unlong = 42;

    // Check enough arguments.

    if (argc != 2)
    {
        cout << "Not enough arguments."
             << "\n";
        return 1;
    }

    // Convert to ulong WITH CHECKING!

    unlong = strtoul(argv[1], &pCh, 10);

    // Ensure argument was okay.

    if ((pCh == argv[1]) || (*pCh != '\0'))
    {
        cout << "Invalid number: " << argv[1]
             << "\n";
        return 1;
    }

    // Output converted argument and exit.

    cout << F16ConvertToF32(unlong);
    return 0;
}