The goal of this assignment is to implement procedures/functions using x86 assembly. In addition to implementing procedures/functions, this assignment requires to pass arguments using the stack. Another important goal is to practice using the logic operations to do bitwise manipulation.
Implement a procedure that mimics a logic unit. The logic unit has one input, one output and a set of control flags. The input size is 32 bits (4 bytes). The output size is 8 bits (1 byte) and there are 32 bits of control signals. See block diagram:
The output depends on the value of the control signals. Your job is to implement the functionality of this unit as follows:
The input is a double word. The bytes are numbered as follows:
Depending on the control signals, the output is determined as indicated in the following table:
Control Signals Output
XXXX XXX0 XXXX XXX0 XXXX XXX0 XXXX XXX1 BYTE 1
XXXX XXX0 XXXX XXX0 XXXX XXX1 XXXX XXX0 BYTE 2
XXXX XXX0 XXXX XXX1 XXXX XXX0 XXXX XXX0 BYTE 3
XXXX XXX1 XXXX XXX0 XXXX XXX0 XXXX XXX0 BYTE 4
ANY OTHER SEE BELOW
*Note: X means 0 or 1. Output for ANY OTHER control signals: Concatenate the two highest order bits of each of the input bytes to form the output byte.
The input, control signals and output are parameters to the procedure you will be implementing. You need to read the parameters from the stack. You are NOT allowed to use the parameter variable names or create new variables in your procedure.
Implement a procedure that manipulates bits in a double word input by calling four different functions. Each function will manipulate one of the bytes in the input and generate one of the output bytes. Each function takes a 32 bit input (4 bytes) and returns a 32 bit output. Within the procedure you have to call four functions to perform different bit operations on the input and generate the output. The functions to implement are the following:
MIRROR_BYTE(input) -- Mirrors value of Byte 4 (leftmost).
Example: IF Byte 4 is 1011 0100 THEN return 0010 1101
SWAP_NIBBLES(input) -- Return interchanged nibbles of input's Byte 3.
Example IF Byte 3 is 1111 0000 THEN Return 0000 1111
INVERT_BITS(input) -- Flip the bits at positions 7, 5, 3, 1 of Byte 2. Leave the rest of the bits unchanged.
Example: IF Byte 2 is 0000 0000 THEN return 1010 1010.
Example: IF Byte 2 is 1111 1111 THEN return 0101 0101.
POWER_TWO(input) -- If the number in Byte 1 is a power of 2, return 1. Otherwise return 0.
Example: IF Byte 1 is 0110 0111 THEN return 0000 0000.
Example: IF Byte 1 is 0100 0000 THEN return 0000 0001.
You have to call the four functions from inside your procedure and pass the input parameter to each function using the stack. Return the result of each function using the return register EAX. The final output of your procedure is 4 bytes. Store the result of each function in the corresponding byte of the procedure's final output, e.g. INVERT_BITS result goes into Byte 2 of the output (since it manipulates Byte 2 of the input).