produce: adds a hashCode implementation for #25.

produce.go

@@ -430,3 +430,26 @@ func readInput(wg *sync.WaitGroup, signals chan struct{}, stdin chan string, out
 		}
 	}
 }
+
+// hashCode imitates the behavior of the JDK's Object#hashCode method.
+// https://docs.oracle.com/javase/7/docs/api/java/lang/String.html#hashCode()
+//
+// TODO: utf16 vs utf8
+func hashCode(s string) int32 {
+	var hc, c, n int32
+	for range s {
+		n++
+	}
+
+	for _, r := range s {
+		c++
+		var p int32 = 1
+		for i := c; i < n; i++ {
+			p *= 31
+		}
+
+		hc += r * p
+	}
+
+	return hc
+}

produce_test.go

@@ -6,6 +6,46 @@ import (
 	"testing"
 )
 
+func TestHashCode(t *testing.T) {
+
+	data := []struct {
+		in       string
+		expected int32
+	}{
+		{
+			in:       "",
+			expected: 0,
+		},
+		{
+			in:       "a",
+			expected: 97,
+		},
+		{
+			in:       "b",
+			expected: 98,
+		},
+		{
+			in:       "⌘",
+			expected: 8984,
+		},
+		{
+			in:       "hashCode",
+			expected: 147696667,
+		},
+		{
+			in:       "c03a3475-3ed6-4ed1-8ae5-1c432da43e73",
+			expected: 1116730239,
+		},
+	}
+
+	for _, d := range data {
+		actual := hashCode(d.in)
+		if actual != d.expected {
+			t.Errorf("expected %v but found %v\n", d.expected, actual)
+		}
+	}
+}
+
 func TestProduceParseArgs(t *testing.T) {
 	configBefore := config
 	defer func() {