How to get the sign, mantissa and exponent of a floating point number
c, emulation, floating-point
Solution
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
Problem
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; } ```