util: Fix RevHash func.

Previous version was not working properly. New one is validated with a
test.

util/util.go

@@ -45,15 +45,14 @@ func ReverseToInt(s string) (int32, error) {
 
 // RevHash reverses a hash in string format.
 func RevHash(hash string) string {
-	revHash := ""
-	for i := 0; i < 7; i++ {
-		j := i * 8
-		part := fmt.Sprintf("%c%c%c%c%c%c%c%c",
-			hash[6+j], hash[7+j], hash[4+j], hash[5+j],
-			hash[2+j], hash[3+j], hash[0+j], hash[1+j])
-		revHash += part
+	rev := []rune(hash)
+	for i := 0; i <= len(rev)/2-2; i += 2 {
+		opp := len(rev) - 2 - i
+		rev[i], rev[opp] = rev[opp], rev[i]
+		rev[i+1], rev[opp+1] = rev[opp+1], rev[i+1]
 	}
-	return revHash
+
+	return string(rev)
 }
 
 // DiffToTarget converts a whole number difficulty into a target.

util/util_test.go

@@ -0,0 +1,24 @@
+package util
+
+import "testing"
+
+func TestRevHash(t *testing.T) {
+	tests := []struct {
+		name string
+		hash string
+		want string
+	}{
+		{
+			"ok",
+			"f82aadcc5f683978c0cf7b616b41f956bb6c4bbd073e93ccffb868972e000000",
+			"0000002e9768b8ffcc933e07bd4b6cbb56f9416b617bcfc07839685fccad2af8",
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			if got := RevHash(tt.hash); got != tt.want {
+				t.Errorf("RevHash() = %v, want %v", got, tt.want)
+			}
+		})
+	}
+}