This is a follow-up to my question yesterday:

CMS kindly provided this example of using bitwise operators to add two numbers in C:

#include<stdio.h>

int add(int x, int y) {
    int a, b;
    do {
        a = x & y;
        b = x ^ y;
        x = a << 1;
        y = b;
    } while (a);
    return b;
}

int main( void ){
    printf( "6 + 3 = %d", add(6,3));
    printf( "6 - 3 = %d", add(6,-3));
    return 0;
}

It works great and I then ported it to Python as follows:

def add(x, y):
    while True:
        a = x & y
        b = x ^ y
        x = a << 1
        y = b
        if a == 0:
            break
    return b

print "6 + 3 = %d" % add(6,3)
print "6 - 3 = %d" % add(6,-3)

They both work for addition and the C program works for subtraction as well. However, the Python program enters an infinite loop for subtraction. I am trying to get to the bottom of this and have posted the program here for further experimentation: http://codepad.org/pb8IuLnY

Can anyone advise why there would be a difference between the way C handles this and the way CPython handles this?

python low-level
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