mirror of
https://github.com/octoleo/syncthing.git
synced 2024-11-05 21:07:58 +00:00
1e2379df1b
The previous implementation was very generic; its tests didn't cover the actual alphabet for device IDs. Benchmark results on amd64: name old time/op new time/op delta Luhnify-8 1.00µs ± 1% 0.28µs ± 4% -72.38% (p=0.000 n=9+10) Unluhnify-8 992ns ± 2% 274ns ± 1% -72.39% (p=0.000 n=10+9)
47 lines
1.0 KiB
Go
47 lines
1.0 KiB
Go
// Copyright (C) 2014 The Protocol Authors.
|
|
|
|
package protocol
|
|
|
|
import "fmt"
|
|
|
|
var luhnBase32 = "ABCDEFGHIJKLMNOPQRSTUVWXYZ234567"
|
|
|
|
func codepoint32(b byte) int {
|
|
switch {
|
|
case 'A' <= b && b <= 'Z':
|
|
return int(b - 'A')
|
|
case '2' <= b && b <= '7':
|
|
return int(b + 26 - '2')
|
|
default:
|
|
return -1
|
|
}
|
|
}
|
|
|
|
// luhn32 returns a check digit for the string s, which should be composed
|
|
// of characters from the alphabet luhnBase32.
|
|
// Doesn't follow the actual Luhn algorithm
|
|
// see https://forum.syncthing.net/t/v0-9-0-new-node-id-format/478/6 for more.
|
|
func luhn32(s string) (rune, error) {
|
|
factor := 1
|
|
sum := 0
|
|
const n = 32
|
|
|
|
for i := range s {
|
|
codepoint := codepoint32(s[i])
|
|
if codepoint == -1 {
|
|
return 0, fmt.Errorf("digit %q not valid in alphabet %q", s[i], luhnBase32)
|
|
}
|
|
addend := factor * codepoint
|
|
if factor == 2 {
|
|
factor = 1
|
|
} else {
|
|
factor = 2
|
|
}
|
|
addend = (addend / n) + (addend % n)
|
|
sum += addend
|
|
}
|
|
remainder := sum % n
|
|
checkCodepoint := (n - remainder) % n
|
|
return rune(luhnBase32[checkCodepoint]), nil
|
|
}
|