Initial version

serial/serial.go

@@ -0,0 +1,61 @@
+const (
+    letters = 26
+    numbers = 900 // 100–999
+    block   = letters * letters * letters * numbers // 26^3 * 900
+)
+
+func Encode(code string) (uint32, error) {
+    // Verwacht formaat: L1L2-NNN-L3-C  => lengte 10, posities: 0,1,3,4,5,7,9
+    if len(code) != 10 || code[2] != '-' || code[6] != '-' || code[8] != '-' {
+        return 0, errors.New("invalid format, expected LL-NNN-L-C")
+    }
+
+    l1, l2, l3 := code[0], code[1], code[7]
+
+    // letters checken
+    // forbidden alleen op l1,l2
+    // nummer parsen uit code[3:6]
+
+    L1 := int(l1 - 'A')
+    L2 := int(l2 - 'A')
+    L3 := int(l3 - 'A')
+    N  := num - 100
+
+    idx := uint32((((L1*letters + L2)*letters + L3) * numbers) + N)
+
+    if code[9] != checksumLetter(idx) {
+        return 0, errors.New("invalid checksum")
+    }
+
+    return idx, nil
+}
+
+func Decode(idx uint32) (string, error) {
+    if idx >= block {
+        return "", errors.New("index out of range")
+    }
+
+    x := int(idx)
+
+    L1 := x / (letters * letters * numbers)
+    r1 := x % (letters * letters * numbers)
+
+    L2 := r1 / (letters * numbers)
+    r2 := r1 % (letters * numbers)
+
+    L3 := r2 / numbers
+    N  := r2 % numbers
+
+    l1 := byte('A' + L1)
+    l2 := byte('A' + L2)
+    l3 := byte('A' + L3)
+
+    if isForbiddenPair(l1, l2) {
+        return "", errors.New("forbidden letter combination")
+    }
+
+    c := checksumLetter(idx)
+
+    return fmt.Sprintf("%c%c-%03d-%c-%c", l1, l2, N+100, l3, c), nil
+}
+