87 lines
1.7 KiB
Go
87 lines
1.7 KiB
Go
package serial
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import (
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"errors"
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"fmt"
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"log"
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)
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const (
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MaxIndex = block
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letters = 26
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numbers = 900 // 100–999
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block = letters * letters * letters * numbers // 26^3 * 900
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)
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func Encode(code string) (uint32, error) {
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log.Printf("code: %v", code)
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// Verwacht formaat: L1L2-NNN-L3-C => lengte 10, posities: 0,1,3,4,5,7,9
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if len(code) != 10 || code[2] != '-' || code[6] != '-' || code[8] != '-' {
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return 0, errors.New("invalid format, expected LL-NNN-L-C")
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}
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l1, l2, l3 := code[0], code[1], code[7]
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n1, n2, n3 := code[3], code[4], code[5]
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// letters checken
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// forbidden alleen op l1,l2
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// nummer parsen uit code[3:6]
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L1 := uint32(l1 - 'A')
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L2 := uint32(l2 - 'A')
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L3 := uint32(l3 - 'A')
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num := uint32(n1*100 + n2*10 + n3)
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N := num - 100
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idx := uint32((((L1*letters+L2)*letters + L3) * numbers) + N)
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if code[9] != checksumLetter(idx) {
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return 0, errors.New("invalid checksum")
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}
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log.Printf("idx: %v", idx)
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return idx, nil
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}
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func Decode(idx uint32) (string, error) {
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log.Printf("idx: %v", idx)
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if idx >= block {
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return "", errors.New("index out of range")
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}
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x := int(idx)
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L1 := x / (letters * letters * numbers)
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r1 := x % (letters * letters * numbers)
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L2 := r1 / (letters * numbers)
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r2 := r1 % (letters * numbers)
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L3 := r2 / numbers
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N := r2 % numbers
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l1 := byte('A' + L1)
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l2 := byte('A' + L2)
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l3 := byte('A' + L3)
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if IsForbiddenPair(l1, l2) {
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return "", errors.New("forbidden letter combination")
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}
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c := checksumLetter(idx)
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code := fmt.Sprintf("%c%c-%03d-%c-%c", l1, l2, N+100, l3, c)
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log.Printf("code: %v", code)
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return code, nil
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}
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func checksumLetter(idx uint32) byte {
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return byte('A' + idx%26)
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}
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func IsForbiddenPair(l1, l2 byte) bool {
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return false
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}
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