Casting float to int (bitwise) in C

Question

Given the 32 bits that represent an IEEE 754 floating-point number, how can the number be converted to an integer, using integer or bit operations on the representation (rat

Answer 1

You can cast the float using a reference. A cast like this should never generate any code.

C++

float f = 1.0f;
int i = (int &)f;
printf("Float %f is 0x%08x\n", f, i);

Output:

Float 1.000000 is 0x3f800000

If you want c++ style cast use a reinterpret_cast, like this.

int i = reinterpret_cast(f);

It does not work with expressions, you have to store it in a variable.

    int i_times_two;
    float f_times_two = f * 2.0f;
    i_times_two = (int &)f_times_two;

    i_times_two = (int &)(f * 2.0f);
main.cpp:25:13: error: C-style cast from rvalue to reference type 'int &'