ex_go_secret-handshake/secret_handshake.go

// Package secret converts an integer value into a secret phrase.
package secret

// Define friendly names for the bitmasks.
const (
	wnk int = 1 << iota // 00001
	bli                 // 00010
	clo                 // 00100
	jmp                 // 01000
	rev                 // 10000
)

// Handshake receives an integer argument and returns a string slice with
// the code words in the proper sequence.
func Handshake(i int) (h []string) {
	// Return the original nil slice if the integer is negative.
	if i < 0 {
		return h
	}

	// Store the handshake phrases in a string slice (maps are slow).
	s := []string{"wink", "double blink", "close your eyes", "jump"}

	// Define an ordered set of keys.
	keys := []int{wnk, bli, clo, jmp}

	// Build the string slice by bitmasking the integer.
	for n, k := range keys {
		if i&k != 0 {
			h = append(h, s[n])
		}
	}

	// Reverse the slice (in-place) if the 5th bit is set.
	if i&rev != 0 {
		for i, j := 0, len(h)-1; i < j; i, j = i+1, j-1 {
			h[i], h[j] = h[j], h[i]
		}
	}

	return h
}

// Revision 2 benchmark:
//
// PASS
// BenchmarkHandshake-12	 5000000	       338 ns/op