~mendelmaleh/checksum

checksum/verhoeff.go -rw-r--r-- 1.1 KiB
3c2ecf21Mendel E Luhn optimizations 11 months ago
                                                                                
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
package checksum

// https://en.m.wikibooks.org/wiki/Algorithm_Implementation/Checksums/Verhoeff_Algorithm#C
var (
	mult = [10][10]int{
		{0, 1, 2, 3, 4, 5, 6, 7, 8, 9},
		{1, 2, 3, 4, 0, 6, 7, 8, 9, 5},
		{2, 3, 4, 0, 1, 7, 8, 9, 5, 6},
		{3, 4, 0, 1, 2, 8, 9, 5, 6, 7},
		{4, 0, 1, 2, 3, 9, 5, 6, 7, 8},
		{5, 9, 8, 7, 6, 0, 4, 3, 2, 1},
		{6, 5, 9, 8, 7, 1, 0, 4, 3, 2},
		{7, 6, 5, 9, 8, 2, 1, 0, 4, 3},
		{8, 7, 6, 5, 9, 3, 2, 1, 0, 4},
		{9, 8, 7, 6, 5, 4, 3, 2, 1, 0},
	}

	perm = [8][10]int{
		{0, 1, 2, 3, 4, 5, 6, 7, 8, 9},
		{1, 5, 7, 6, 2, 8, 3, 0, 9, 4},
		{5, 8, 0, 3, 7, 9, 6, 1, 4, 2},
		{8, 9, 1, 6, 0, 4, 3, 5, 2, 7},
		{9, 4, 5, 3, 1, 2, 6, 8, 7, 0},
		{4, 2, 8, 6, 5, 7, 3, 9, 0, 1},
		{2, 7, 9, 3, 8, 0, 6, 4, 1, 5},
		{7, 0, 4, 6, 9, 1, 3, 2, 5, 8},
	}

	inv = [10]int{0, 4, 3, 2, 1, 5, 6, 7, 8, 9}
)

func verhoeff(i, n, c int) int {
	return mult[c][perm[i%8][n]]
}

// Verhoeff checksum validation
func Verhoeff(num int) bool {
	return IterInt(num, verhoeff) == 0
}

// GetVerhoeff calculates the Verhoeff checksum digit for num.
func GetVerhoeff(num int) int {
	return inv[IterInt(num*10, verhoeff)]
}