using unions with float and long

[Rau_ashaman]

i need to know how to use unions to extract and return the sign, the intended exponent value and the full 24-bit mantissa from a 32-bit floating-point number. I know that it has something to do with using the fact that the two share the same space because of the union, but i'm not too sure on the coding to make the values apparant...

[Dave McLelland]

typedef union {
    float FloatVal;
    struct {
        unsigned int SignBit:1;        // 1 bit for the sign
        unsigned int Exponent:7;    // 7 bits for the exponent
        unsigned int Mantissa:24;   // 24 bits for the mantissa
    } FloatBits;
} FLOAT;

FLOAT f;
f.FloatVal = 1.234f;

Basically all the elements in a union occupy the same space in memory. A union simply defines a set of templates (names and types) for accessing that memory.

So. The above allows you to declare a variable of type FLOAT and access its memory (4 bytes) as a float (f.FloatVal) or as a set of bit fields representing the individual parts that make up the float representation f.FloatBits.Exponent etc.

(ps. I have not compiled the above, but it should be enough to point you in the right direction if it dosent work)

[Rau_ashaman]

thanks heaps, thats what i was looking for, well it was enough to point me in the right direction. thanks again.