example of conveting float numbers to ieee 754 in single and double precison format.

convert_float_to_ieee754.c

#include <stdio.h>
#include <stdint.h>
#include <inttypes.h>

/*
 * See also : http://class.ece.iastate.edu/arun/CprE281_F05/ieee754/ie5.html
 */

union FloatingPointSinglePrecisionIEEE754 {
  struct {
    unsigned int mantissa : 23;
    unsigned int exponent : 8;
    unsigned int sign : 1;
  } raw;
  float f;
} fnumber;

union FloatingPointDoublePrecisionIEEE754 {
  struct {
    uint64_t mantissa : 52;
    uint64_t exponent : 11;
    uint64_t sign : 1;
  } raw;
  double d;
} dnumber;

int main() {
  printf("sign\texponent\tmantissa\n");

  fnumber.f = -6.8;
  printf("%x\t%x\t\t%x\n",
    fnumber.raw.sign,
    fnumber.raw.exponent,
    fnumber.raw.mantissa); 

  dnumber.d = -6.8;
  printf("%x\t%x\t\t%" PRIx64 "\n",
    dnumber.raw.sign,
    dnumber.raw.exponent,
    (uint64_t)dnumber.raw.mantissa);

  return 0;
}