Question

For integer values, it is pretty straightforward the difference in little endian and big endian representation.

But it is not clear for me how a little endian float differs from a big endian float.

And finally, I would like to know which is more commonly used.

Answer 1

Some sources say IEEE754 floats are always stored little-endian but The IEEE754 specification for floating point numbers simply doesn’t cover the endianness problem and may vary from machine to machine.
Here is sample code for floating point / byte array conversion:

#include <stdio.h>

int main(int argc, char** argv){
  char *a;
  float f = 3.14159;  // number to start with

  a = (char *)&f;   // point a to f's location

  // print float & byte array as hex
  printf("float: %f\n", f);
  printf("byte array: %hhX:%hhX:%hhX:%hhX\n", \
    a[0], a[1], a[2], a[3]);

  // toggle the sign of f -- using the byte array
  a[3] = ((unsigned int)a[3]) ^ 128;

  //print the numbers again
  printf("float: %f\n", f);
  printf("byte array: %hhX:%hhX:%hhX:%hhX\n", \
    a[0], a[1], a[2], a[3]);

  return 0;
}

It’s output on a little-indian machine:

float: 3.141590
byte array: D0:F:49:40
float: -3.141590
byte array: D0:F:49:C0

Theoretically, on a big-endian machine the order of bytes would be reversed.

Reference:
http://betterexplained.com/articles/understanding-big-and-little-endian-byte-order/