C / C++ / MFC

lgmanuel wrote:

am trying to swap the values of 'x' and 'y' without using a temporary storage like 'z'..

template<class A>
void xswap(A& a, A& b)
{
    for(size_t i=0; i<sizeof(a); ++i)
    {
        ((char*)&a)[i] ^= ((char*)&b)[i];
        ((char*)&b)[i] ^= ((char*)&a)[i];
        ((char*)&a)[i] ^= ((char*)&b)[i];
    }
}

2 bugs found.
> recompile ...
65534 bugs found.

int x = 150;
int y = 45;
asm{
   LDA x;
   LDB y;
   STA y;
   STB x;
}

#DEFINE B 1
int x = 150;
int y = 45;
asm{
   /* x ^= y */
   LDA x;  /* A register = x */
   XOR y;  /* A = A XOR y */
   STA x;  /* x = A, i.e., x ^= y */

   /* y ^= x */
   STA B;  /* B register = x */
   LDA y;  /* A register = y */
   XOR B;  /* A = A XOR B */
   STA y;  /* y = A, i.e., y ^= x  */

   /* x ^= y */
   STA B;  /* B register = y */
   LDA x;  /* A register = x */
   XOR B;  /* A = A XOR B */
   STA x;  /* x = A, i.e., x ^= y  */
}

#DEFINE B 1
int x = 150;
int y = 45;
asm{
   /* x = x + y; */
   LDA x;  /* A register = x */
   LDB y;  /* B register = y */
   ADA B;  /* A register = A + B, i.e. A = x + y */
   STA x;  /* Save A register to x */

   /* y = x - y */
   /* A contains x, B contains y */
   CMB;   /* 1's complement B register, i.e. B = -y -1 */
   INB;   /* increment (2's complement) B , i.e. B = -y */
   ADA B; /* Add B (-y) to A (x), i.e. A = x - y */
   STA y; /* Save A register to y */

   /* x = x - y */
   /* At this point, A contains y */
   CMA;   /* 1's complement A register, i.e. A = -y -1 */
   INA;   /* increment A (2's complement), i.e. A = -y */
   ADA x; /* Add x to A, i.e., A = -y + x */
   STA x; /* Save A register to x */
}

int x = 450;
int y = 45;
Console.WriteLine("X = " + y);
Console.WriteLine("Y = " + x);

x^=y;
y^=x;
x^=y;