Verhoeff algorithm: Difference between revisions

=={{header|Nim}}==

<lang Nim>import strformat

const

D = [[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]]

Inv = [0, 4, 3, 2, 1, 5, 6, 7, 8, 9]

P = [[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]]

type Digit = 0..9

proc verhoeff[T: SomeInteger](n: T; validate, verbose = false): T =

## Compute or validate a check digit.

## Return the check digit if computation or the number with the check digit

## removed if validation.

## If not in verbose mode, an exception is raised if validation failed.

doAssert n >= 0, "Argument must not be negative."

# Extract digits.

var digits: seq[Digit]

if not validate: digits.add 0

var val = n

while val != 0:

digits.add val mod 10

val = val div 10

if verbose:

echo if validate: &"Check digit validation for {n}:" else: &"Check digit computation for {n}:"

echo " i ni p(i, ni) c"

# Compute c.

var c = 0

for i, ni in digits:

let p = P[i mod 8][ni]

c = D[c][p]

if verbose: echo &"{i:2} {ni} {p} {c}"

if validate:

if verbose:

let verb = if c == 0: "is" else: "is not"

echo &"Validation {verb} successful.\n"

elif c != 0:

raise newException(ValueError, &"Check digit validation failed for {n}.")

result = n div 10

else:

result = Inv[c]

if verbose: echo &"The check digit for {n} is {result}.\n"

for n in [236, 12345]:

let d = verhoeff(n, false, true)

discard verhoeff(10 * n + d, true, true)

discard verhoeff(10 * n + 9, true, true)

let n = 123456789012

let d = verhoeff(n)

echo &"Check digit for {n} is {d}."

discard verhoeff(10 * n + d, true)

echo &"Check digit validation was successful for {10 * n + d}."

try:

discard verhoeff(10 * n + 9, true)

except ValueError:

echo getCurrentExceptionMsg()</lang>

{{out}}

<pre>Check digit computation for 236:

i ni p(i, ni) c

0 0 0 0

1 6 3 3

2 3 3 1

3 2 1 2

The check digit for 236 is 3.

Check digit validation for 2363:

i ni p(i, ni) c

0 3 3 3

1 6 3 1

2 3 3 4

3 2 1 0

Validation is successful.

Check digit validation for 2369:

i ni p(i, ni) c

0 9 9 9

1 6 3 6

2 3 3 8

3 2 1 7

Validation is not successful.

Check digit computation for 12345:

i ni p(i, ni) c

0 0 0 0

1 5 8 8

2 4 7 1

3 3 6 7

4 2 5 2

5 1 2 4

The check digit for 12345 is 1.

Check digit validation for 123451:

i ni p(i, ni) c

0 1 1 1

1 5 8 9

2 4 7 2

3 3 6 8

4 2 5 3

5 1 2 0

Validation is successful.

Check digit validation for 123459:

i ni p(i, ni) c

0 9 9 9

1 5 8 1

2 4 7 8

3 3 6 2

4 2 5 7

5 1 2 5

Validation is not successful.

Check digit for 123456789012 is 0.

Check digit validation was successful for 1234567890120.

Check digit validation failed for 1234567890129.</pre>