#include #include #include #include /** * A bitwise integer calculator * Performs addition, subtraction, multiplication, and integer division without regard to sign. * @uthor: @ce * Bugs: Error handling not complete. * Version: * 0.0.0.0: Initial Release * 0.0.0.1: Patch added to address error-handling. Please enter 2 integers on the same line. i.e. 42 5 * 0.0.0.2: Added compatibility to compute larger than values * 0.0.0.3: divide bug addressed and fixed. Thanks @Baptiste */ int readNum(int &, int &); long int add(int, int); long int subtract(int, int); long int multiply(int, int); int divide(int, int); int main() { int x=0, y=0; srand(time(NULL)); if(readNum(x, y) == EXIT_FAILURE) { perror("Failure to read integers. Random value used!\n"); x = rand() % 100; y = add(rand() % 100, 1); printf("%d is used as 1st number! %d is used as 2nd number!\n", x, y); } printf("%d + %d = %ld\n", x, y, add(x, y)); printf("%d - %d = %ld\n", x, y, subtract(x, y)); printf("%d * %d = %ld\n", x, y, multiply(x, y)); if(y) { printf("%d / %d = %d\n", x, y, divide(x, y)); }else { perror("For division, 2nd integer cannot be zero. Default used!\n"); y = add((rand() % 100), 1); printf("%d is used as 2nd number!\n", y); printf("%d\n", divide(x, y)); } return 0; } /* * Safely reads in 2 integers if possible * @return 0 if no integer was read, 1 otherwise. */ int readNum(int &x, int &y) { char* line = (char*)malloc(101*sizeof(char)); //process the input as a string first if(!line) { perror("malloc failure"); return EXIT_FAILURE; } fgets(line, 101*sizeof(char), stdin); if(line) { if(sscanf(line, "%d%d", &x, &y)==2) return EXIT_SUCCESS; } //if we reach here, no valid input was entered or we have a null pointer. return EXIT_FAILURE; } /* * Made long to accomodate for possible int overflow */ long int add(int x, int y) { return y ? add(x ^ y, (x & y) << 1) : x; } /* * Made long to accomodate for possible int overflow */ long int subtract(int x, int y) { return y ? subtract(x ^ y, (~x & y) << 1) : x; } /* * Made long to accomodate for possible int overflow */ long int multiply(int x, int y) { if(!x || !y) return 0; if(y==1) return x; if(x==1) return y; /*swap x and y if x < y*/ if (x < y) (x ^= y), (y ^= x), (x ^= y); long product = 0; while(x) { if(x & 1) // If x is odd product = add(product, y); x >>= 1; // Note: This must set highest order bit ZERO. It must not copy the sign bit. y <<= 1; } return product; } int divide(int n, int d) { int sign = 0; //check sign both on dividend and divisor in case we are dealing with a negative number. We need to check the signed bit for this if ((n & (1 << 31)) == (1 << 31)) { // Check for signed bit sign = !sign; // Negation - to get 2s complement n = add(~n, 1); } if((d & (1 << 31)) == (1 << 31)) { sign = !sign; d = add(~d, 1); } int quotient = 0; long r; for (int i = 30; i >= 0; i = subtract(i, 1)) { // Left shift divisor until it's smaller than dividend r = (d << i); if ((r < INT_MAX && r > 0) && (r <= n)) { // Avoid cases where comparison between long and int doesn't make sense quotient |= (1 << i); n = subtract(n, (int) r); } } if (sign) quotient = add(~quotient, 1); return quotient; }

BitwiseCalculator