Answer Posted / krichait

Hello... this is the way to write......

// Add two ints using bitwise operators

public class ArithWithBitOps {

//------------------------------------------------------------------------------
// Second attempt - Go bit by bit right to left doing
binary arith
static int carry = 0; // c=1 for 1+1

static int add2(int a, int b) {
int sum = 0; // get sum here
int mask = 1; // shifting mask used
to test each bit

while(mask != 0) {
int ta = a & mask; // get next bit
to add
int tb = b & mask; // get next bit
to add
int bsum = bitAdd2(ta, tb, mask); // add the bits
& set carry
if(Testing) System.out.print("ta=" + ta + ", tb=" +
tb + ", bsum=" + bsum
+ ", carry=" + carry + ", b4sum="
+ sum);
sum = (sum | bsum); // OR in the
results
if(Testing) System.out.println(", aft sum=" + sum);
mask = mask << 1; // move to next bit
} // end while() thru bits

if(carry > 0) System.err.println(">>>>>>>>>>>>losing
carry");
return sum;
} // end add2()

//----------------------------------------------------------
// Add two selected bits in x and y & set carry if carry
static int bitAdd2(int x, int y, int bsel) {
// System.out.println("bitAdd2 of " + x + " " + y);
int tx = x & bsel;
int ty = y & bsel;
if(carry == 1) { // Have carry ?
if((tx & ty) != 0) {
carry = 1;
return bsel; // 1 + 1 + c=1 -> 1 + c=1
}else if((tx ^ ty) != 0) {
carry = 1;
return 0; // 1 + 0 + c=1 -> 0 + c=1
}else {
carry = 0;
return bsel; // 0 + 0 + c=1 -> 1 + c=0
}
}else if (carry == 0) { // no carry
if((tx & ty) > 0) {
carry = 1;
return 0; // 1 + 1 + c=0 -> 0 + c=1
}else if((tx ^ ty) != 0) {
carry = 0;
return bsel; // 1 + 0 + c=0 -> 1 + c=0
}else {
System.out.println("(tx ^ ty)=" + (tx ^ ty));
carry = 0;
return 0; // 0 + 0 + c=0 -> 0 + c=0
}
}else {
System.err.println("Invalid carry= " + carry);
return 0;
}
} // end bitAdd2()

//------------------------------------------------
// Test the above
public static void main(String[] args) {
// The numbers to add
int x = -24;
int y = 15;

if(Testing) System.out.println("Max int=" +
Integer.MAX_VALUE //Max int=2147483647
+ " " + Integer.toHexString(-2) //-2=fffffffe
+ " " + 0x80000000); //-2147483648
int sum = add2(x, y);
System.out.println("Final sum= " + sum + " vs " + (x +
y) + " " + Integer.toHexString(sum));
//Final sum= -9 vs -9 fffffff7
} // end main()

static final boolean Testing = false; // global flag for
debug output
}

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