Step by Step solution about How to resolve the algorithm Four bit adder step by step in the C programming language

This C code implements a 4-bit full adder, a digital circuit that performs addition of two 4-bit binary numbers. It includes functions for a half adder (adds two bits) and a full adder (adds three bits) and the main function that tests the 4-bit adder. Here's a detailed breakdown:

• Custom Data Type and Macros:

  • typedef char pin_t;: Defines a custom data type pin_t to represent a single bit or "pin."
  • Macros like IN and OUT are used to indicate input and output pins, respectively.
  • PIN(X) is a macro to define a pin named X as static.

• Half Adder (Function halfadder):

  • Takes two input pins a and b and outputs two pins s (sum) and c (carry).
  • Uses the XOR gate (XOR(V(a), V(b))) to calculate the sum and the AND gate (V(a) & V(b)) to calculate the carry.

• Full Adder (Function fulladder):

  • Takes three input pins a, b, and ic (carry-in) and outputs two pins s (sum) and oc (carry-out).
  • Internally, it uses two halfadder functions to calculate the sum and carry.
  • The carry-out is calculated as V(tc) | V(pc), where tc is the carry from the first half adder, and pc is the carry from the second half adder.

• 4-Bit Adder (Function fourbitsadder):

  • Takes four input bits for each operand (a and b) and four output bits for the sum (o).
  • It uses three fulladder functions to calculate the sum and carry for each bit position.

• Main Function:

  • Initializes input and output pins for the 4-bit addition.
  • Sets input values for testing: a = 0001 and b = 0111.
  • Calls the fourbitsadder function to perform the addition.
  • Prints the input values, sum, and overflow flag.

In summary, this code simulates a 4-bit binary adder using functions that implement half and full adders. It takes two 4-bit binary numbers as input and outputs their sum and an overflow flag.

#include <stdio.h>

typedef char pin_t;
#define IN const pin_t *
#define OUT pin_t *
#define PIN(X) pin_t _##X; pin_t *X = & _##X;
#define V(X) (*(X))

/* a NOT that does not soil the rest of the host of the single bit */
#define NOT(X) (~(X)&1)

/* a shortcut to "implement" a XOR using only NOT, AND and OR gates, as
   task requirements constrain */
#define XOR(X,Y) ((NOT(X)&(Y)) | ((X)&NOT(Y)))

void halfadder(IN a, IN b, OUT s, OUT c)
{
  V(s) = XOR(V(a), V(b));
  V(c) = V(a) & V(b);
}

void fulladder(IN a, IN b, IN ic, OUT s, OUT oc)
{
  PIN(ps); PIN(pc); PIN(tc);

  halfadder(/*INPUT*/a, b, /*OUTPUT*/ps, pc);
  halfadder(/*INPUT*/ps, ic, /*OUTPUT*/s, tc);
  V(oc) = V(tc) | V(pc);
}

void fourbitsadder(IN a0, IN a1, IN a2, IN a3,
		   IN b0, IN b1, IN b2, IN b3,
		   OUT o0, OUT o1, OUT o2, OUT o3,
		   OUT overflow)
{
  PIN(zero); V(zero) = 0;
  PIN(tc0); PIN(tc1); PIN(tc2);

  fulladder(/*INPUT*/a0, b0, zero, /*OUTPUT*/o0, tc0);
  fulladder(/*INPUT*/a1, b1, tc0,  /*OUTPUT*/o1, tc1);
  fulladder(/*INPUT*/a2, b2, tc1,  /*OUTPUT*/o2, tc2);
  fulladder(/*INPUT*/a3, b3, tc2,  /*OUTPUT*/o3, overflow);
}


int main()
{
  PIN(a0); PIN(a1); PIN(a2); PIN(a3);
  PIN(b0); PIN(b1); PIN(b2); PIN(b3);
  PIN(s0); PIN(s1); PIN(s2); PIN(s3);
  PIN(overflow);

  V(a3) = 0; V(b3) = 1;
  V(a2) = 0; V(b2) = 1;
  V(a1) = 1; V(b1) = 1;
  V(a0) = 0; V(b0) = 0;

  fourbitsadder(a0, a1, a2, a3, /* INPUT */
		b0, b1, b2, b3,
		s0, s1, s2, s3, /* OUTPUT */
		overflow);

  printf("%d%d%d%d + %d%d%d%d = %d%d%d%d, overflow = %d\n",
	 V(a3), V(a2), V(a1), V(a0),
	 V(b3), V(b2), V(b1), V(b0),
	 V(s3), V(s2), V(s1), V(s0),
	 V(overflow));
  
  return 0;
}