That's pretty neat, the perhaps not universally portable.
Your code does better than just avoiding relational and logical operators,
it also avoids conditional (and loop) statements (including ?: ).
Here's a re-write:
Code:
#include <limits.h> /* for CHAR_BIT: number of bits in a char */
#define INT_BITS (sizeof(int) * CHAR_BIT)
int maximum( int x, int y ) {
int xy[] = { x, y };
return xy[ getSign( x - y )]; /* Index xy by sign of (x-y) */
}
int getSign( int n ) { /* Returns sign bit of n */
/* Shift sign into bit position 0 */
return (unsigned)n >> INT_BITS - 1;
}
One could replace int xy[] = { x, y } by int* xy = &x, but
that assumes (minimally) that x has a lower address than y.
The method is already making an assumption about manipulating
the sign bit that may not work on all computers.
I also found your MinimumOf and MaximumOf interesting:
Code:
/* Fill n with its sign bit, becoming all 1's or 0's */
#define spread_sign(n) ((n) >> (INT_BITS - 1))
/* Return zero if n is positive, otherwise return n */
#define zero_if_positive(n) ((n) & spread_sign(n))
int minimumOf( int a, int b ) {
return b + zero_if_positive( a - b );
}
int maximumOf( int a, int b ) {
return a - zero_if_positive( a - b );
}
