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simple ALU
I am trying to write a simple ALU. I think I am on the right track, but don't really know how I can improve on it. I also dont fully understand what to do with the carryin value? I found this site on google and tried a search but could not find anything related(sorry if it's already been covered). Any tips?
Code:
#include <iostream>
#include <cstdlib>
#include <string>
using namespace std;
int main() {
/*4-bit ALU*/
char A[5] = "0101";
char B[5] = "0011";
char zero[2] = "0";
int a[5];
int b[5];
char Cin[2] = "0";
int Result[5];
/*Makes an int out of input A*/
for(int i=0; i<4; i++){
if(A[i] == zero[0]){
a[i] = 0;
}
else{
a[i] = 1;
}
}
/*Makes an int out of input B*/
for(int i=0; i<4; i++){
if(B[i] == zero[0]){
b[i] = 0;
}
else{
b[i] = 1;
}
}
cout << "4 bit ALU" << endl;
cout << "--------------------";
cout << "\nThe first input is: ";
for(int i=0; i<4; i++){
cout << a[i];
}
cout << "\nThe second input is: ";
for(int i=0; i<4; i++){
cout << b[i];
}
cout << "\nThe carry-in is: ";
for(int i=0;i<1;i++){
cout << Cin[i];
}
cout << "\n--------------------";
/*AND*/
for(int i=0; i<4; i++){
Result[i] = a[i]&b[i];
}
cout << "\nThe Result of AND is: ";
for(int i=0;i<4;i++){
cout << Result[i];
}
cout << "\n";
/*OR*/
for(int i=0; i<4; i++){
Result[i] = a[i]|b[i];
}
cout << "The Result of OR is: ";
for(int i=0;i<4;i++){
cout << Result[i];
}
cout << "\n";
/*XOR*/
for(int i=0; i<4; i++){
Result[i] = a[i]^b[i];
}
cout << "The Result of XOR is: ";
for(int i=0;i<4;i++){
cout << Result[i];
}
cout << "\n";
/*32 bit ALU*/
char A2[33] = "000011111010011001011001";
char B2[33] = "001100101101111000100101";
char zero2[2] = "0";
int a2[33];
int b2[33];
int bb[33];
char Cin2[2] = "0";
int Result2[33];
/*Makes an int out of input A*/
for(int i=0; i<32; i++){
if(A2[i] == zero2[0]){
a2[i] = 0;
}
else{
a2[i] = 1;
}
}
/*Makes an int out of input B*/
for(int i=0; i<32; i++){
if(B2[i] == zero2[0]){
b2[i] = 0;
}
else{
b2[i] = 1;
}
}
/*Makes an int out of input B INVERSE using twos compliment*/
for(int i=0; i<32; i++){
if(B2[i] == zero2[0]){
bb[i] = 1;
}
else{
bb[i] = 0;
}
}
bb[31]++;
cout << "32 bit ALU" << endl;
cout << "--------------------";
cout << "\nThe first input is: ";
for(int i=0; i<32; i++){
cout << a2[i];
}
cout << "\nThe second input is: ";
for(int i=0; i<32; i++){
cout << b2[i];
}
cout << "\nThe INVERSE of the second input is: ";
for(int i=0; i<32; i++){
cout << bb[i];
}
cout << "\nThe carry-in is: ";
for(int i=0;i<1;i++){
cout << Cin2[i];
}
cout << "\n--------------------";
/*AND*/
for(int i=0; i<32; i++){
Result2[i] = a2[i]&b2[i];
}
cout << "\nThe Result of AND is: ";
for(int i=0;i<32;i++){
cout << Result2[i];
}
cout << "\n";
/*OR*/
for(int i=0; i<32; i++){
Result2[i] = a2[i]|b2[i];
}
cout << "The Result of OR is: ";
for(int i=0;i<32;i++){
cout << Result2[i];
}
cout << "\n";
/*XOR*/
for(int i=0; i<32; i++){
Result2[i] = a2[i]^b2[i];
}
cout << "The Result of XOR is: ";
for(int i=0;i<32;i++){
cout << Result2[i];
}
cout << "\n";
/*Sub*/
for(int i=0; i<32; i++){
Result2[i] = a2[i]|bb[i];
}
cout << "The Result of Sub is: ";
for(int i=0;i<32;i++){
cout << Result2[i];
}
cout << "\n";
return 0;
}
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Looks promising.
Make some utility functions to clean main() up.
Eg
Code:
void convertToInt ( int *result, const char *input, int len ) {
/*Makes an int out of input */
for(int i=0; i<len; i++){
if(input[i] == '0' ){
result[i] = 0;
}
else{
result[i] = 1;
}
}
}
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yeah I know my main is messy, thanks for the tip :-) haha
do you have anytips about the logic behind carryin and carryout?
from my understanding 4bit doesnt need carryout but 32 does so that it can handle overflow?
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Eg.
01
11
For addition, you start with carry = 0
Then take the two right-most bits
r = 1 + 1 + carry
In a single bit, r = 0 and the carry is now 1
The next bits would be
r = 0 + 1 + carry
Again, r = 0 and carry is again 1
So our complete result (in 2 bits) is 00 (and carry = 1)
