How to get the sign, mantissa and exponent of a floating point number

Question

I have a program, which is running on two processors, one of which does not have floating point support. So, I need to perform floating point calculations using fixed point in that processor. For that purpose, I will be using a floating point emulation library.

I need to first extract the signs, mantissas and exponents of floating point numbers on the processor which do support floating point. So, my question is how can I get the sign, mantissa and exponent of a single precision floating point number.

Following the format from this figure,

That is what I've done so far, but except sign, neither mantissa and exponent are correct. I think, I'm missing something.

void getSME( int& s, int& m, int& e, float number ) {     unsigned int* ptr = (unsigned int*)&number;      s = *ptr >> 31;     e = *ptr & 0x7f800000;     e >>= 23;     m = *ptr & 0x007fffff; } 

Answer 1

I think it is better to use unions to do the casts, it is clearer.

#include <stdio.h>  typedef union {   float f;   struct {     unsigned int mantisa : 23;     unsigned int exponent : 8;     unsigned int sign : 1;   } parts; } float_cast;  int main(void) {   float_cast d1 = { .f = 0.15625 };   printf("sign = %x\n", d1.parts.sign);   printf("exponent = %x\n", d1.parts.exponent);   printf("mantisa = %x\n", d1.parts.mantisa); } 

Example based on http://en.wikipedia.org/wiki/Single_precision