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package verhoeff
import (
"strconv"
"strings"
"github.com/neonxp/checksum"
)
var d = [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},
}
var p = [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},
}
var inv = [10]int{0, 4, 3, 2, 1, 5, 6, 7, 8, 9}
// Check number is correct by verhoeff algorithm
func Check(number string) error {
c := 0
numbers := strings.Split(number, "")
l := len(numbers)
for i := l; i > 0; i-- {
ch := numbers[i-1]
num, err := strconv.Atoi(string(ch))
if err != nil {
return checksum.ErrInvalidNumber
}
c = d[c][p[(l-i)&7][num]]
}
if c != 0 {
return checksum.ErrInvalidChecksum
}
return nil
}
// Generate checksum (must be added to number at right)
func Generate(number string) (string, error) {
c := 0
numbers := strings.Split(number, "")
l := len(numbers)
for i := l; i > 0; i-- {
ch := numbers[i-1]
num, err := strconv.Atoi(string(ch))
if err != nil {
return "", checksum.ErrInvalidNumber
}
c = d[c][p[(l-i+1)&7][num]]
}
return strconv.Itoa(inv[c]), nil
}
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