Call your file printbin.s. The C caller for this program provides a char to the assembly function printbin. It asks the user for a hex number between 0 and 0xff, converts the input from an ASCII string to a char value, passes it to printbin as an argument, and displays the returned string which should be the ASCII characters for the binary value, e.g. for entry of the hex value 0x3d, you will get the printout: “The binary format for character = is 0011 1101” You can see the function prototype for the printbin function in the calling C code. The function printbin should be C callable using a stack frame and call an assembly language subprogram “donibble” that is not required to be C callable. Avoiding the use of stack frames is one way assembly code can be more efficient than C compiler generated code. The function printbin needs to declare space in the .data section for storage of a string to be returned and return the address of that location in the %eax. While processing the bits of the input argument, keep a pointer to the string in an available register. printbin and donibble can store an ascii character 0x20, 0x30, or 0x31 in the string indirectly via that register and then increment the pointer in that register until the entire return string has been filled in. The donibble function handles one half of the char value producing the four ASCII character (0/1) for the bits in one hex digit. Printbin should call donibble twice once with each nibble to be processed in half of an available register, e.g. the %al. Donibble should scan the 4 bits of the register and move an appropriate ascii code into the string for each bit. Printbin adds the space between the two nibbles.

make printbin
./printbin