Bitwise Float To Int

问题

I am trying to figure out the algorithm to this but all I get with google is doing it with casting. I need to know the details.

So if we have a float x and want to return its binary representation what do we need to do?

I know we need to return the float if its NaN or a infinity but otherwise what are the steps?

EDIT

The function takes in an unsigned int, to be used as if it was a float, and then return the integer the number represents. I cannot use casting, just conditionals and bit-wise operators.

回答1:

Alternatively, use a union:

typedef union 
{
    float f_;
    int   i_;
} FloatBits;

FloatBits fb;

fb.f_ = 1.5;

Then fb.i_ contains the float mapped onto an int to allow extraction of the bits. Again, usual assunptions about the size of types - you can verify these using sizeof.

Using this approach, you can play with setting the bits in fb.i_ directly and seeing them mapped back into the float.

回答2:

To test if a 32-bit value represents NaN if it were a float you can check if its unsigned value is greater than the representation for infinity.

int n = 
if((n & 0x7FFFFFFF) > 0x7f800000) // is NaN

Removing the sign is required as a NaN can have negative sign bit set to 1 (though NaN is not positive or negative)

---

If you want to know if a float is NAN, you can use

float f = NAN
if (f != f) // is NAN

To compare with Infinity

float f = INFINITY;
if (f == INFINITY)

回答3:

The float number in c programming language follows the IEEE Standard for Floating-Point Arithmetic (IEEE 754).

You can convert float to int with the code

int i = *(int *)&f; // f is the float variable you want to convert

And then interpret the int yourself according to IEEE 754 standard.

来源：https://stackoverflow.com/questions/7396591/bitwise-float-to-int