ieee754.cc

#include <iostream>
#include <string>
#include <cstring>
#include <bitset>
#include <cmath>

// Convert the 32-bit binary encoding into hexadecimal
int binary_to_hex(std::string &binary)
{
    std::bitset<32> set(binary);      
    int hex = set.to_ulong();
     
    return hex;
}

void parse_ieee754(std::string &binary) {
    std::string sign = binary.substr(0,1);
    std::string exp  = binary.substr(1,8);
    std::string frac = binary.substr(9,32);
    
    std::cout << binary << " " << binary.length() << std::endl;
    std::cout << sign << " " << sign.length() << std::endl;
    std::cout << exp << " " << exp.length() << std::endl;
    std::cout << frac << " " << frac.length() << std::endl;   
}

// Convert the 32-bit binary into the decimal
float binary_to_f32(std::string &binary)
{
    int hexNr = binary_to_hex(binary);
 
    bool negative  = !!(hexNr & 0x80000000);
    int  exponent  =   (hexNr & 0x7f800000) >> 23;    
    int sign = negative ? -1 : 1;

    std::cout << "exp: " << exponent << ", sign: " << sign << std::endl; 

    // Subtract 127 from the exponent
    exponent -= 127;
 
    // Convert the mantissa into decimal using the
    // last 23 bits
    int power = -1;
    float total = 0.0;
    for ( int i = 0; i < 23; i++ )
    {
        int c = binary[ i + 9 ] - '0';
        total += (float)c * (float)pow(2.0, power);
        power--;
    }
    total += 1.0;
 
    float value = sign * (float)pow(2.0, exponent) * total;
 
    return value;
}

int main() {

    std::string binary = "00111110001000000000000000000000";

    std::cout << binary << std::endl;

    parse_ieee754(binary);

    std::cout << binary_to_hex(binary) << std::endl;

    std::cout << binary_to_f32(binary) << std::endl;

    unsigned long ul = 0x3E200000;
    float f;
    char *pul = (char *)&ul;  // ok, char* can alias any type
    char *pf = (char *)&f;    // ok, char* can alias any type
    memcpy(pf, pul, sizeof(float));
    std::cout << f << std::endl;
}