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LolloDev5123/verhoeff.lua

Created February 9, 2025 14:32
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verhoeff.lua
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verhoeff.lua
--[[
Verhoeff Gumm Check Digit Library in Lua
-----------------------------------------
@lollodev5123
MIT License
Copyright (c) 2025
Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies
of the Software, and to permit persons to whom the Software is furnished to do so,
subject to the following conditions:
The above copyright notice and this permission notice shall be included in all
copies or substantial portions of the Software.
THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED,
INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR
PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE
FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE,
ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
--]]
local verhoeff = {}
-- Multiplication table d (1-indexed; use [digit+1] to index)
local 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}
}
-- Permutation table p (1-indexed; row: ((position mod 8)+1), column: (digit+1))
local 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}
}
-- Inverse table inv (1-indexed; use [digit+1] to index)
local inv = {0,4,3,2,1,5,6,7,8,9}
----------------------------------------------------------------------
-- Generate the Verhoeff check digit.
--
-- @param input (string|table) A number as a string of digits or an array of digits (0–9)
-- @return number The computed check digit (0–9)
----------------------------------------------------------------------
function verhoeff.generate(input)
local c = 0
if type(input) == "string" then
local n = #input
for i = n, 1, -1 do
local ch = input:sub(i, i)
local digit = ch:byte() - 48 -- convert ASCII '0'-'9' to number 0-9
if digit < 0 or digit > 9 then
error("Invalid character '" .. ch .. "' in input string. Expected digits 0–9.")
end
local pos = ((n - i) % 8) + 1
c = d[c + 1][ p[pos][digit + 1] ]
end
elseif type(input) == "table" then
local n = #input
for i = n, 1, -1 do
local digit = input[i]
if type(digit) ~= "number" or digit < 0 or digit > 9 or digit ~= math.floor(digit) then
error("Invalid digit at position " .. i .. " in input table. Expected an integer 0–9.")
end
local pos = ((n - i) % 8) + 1
c = d[c + 1][ p[pos][digit + 1] ]
end
else
error("Input must be a string or a table of digits (0–9).")
end
return inv[c + 1]
end
----------------------------------------------------------------------
-- Validate a number that includes a Verhoeff check digit.
--
-- @param input (string|table) A number (with check digit) as a string or an array of digits (0–9)
-- @return boolean True if the input is valid, false otherwise.
----------------------------------------------------------------------
function verhoeff.validate(input)
local c = 0
if type(input) == "string" then
local n = #input
for i = n, 1, -1 do
local ch = input:sub(i, i)
local digit = ch:byte() - 48
if digit < 0 or digit > 9 then
error("Invalid character '" .. ch .. "' in input string. Expected digits 0–9.")
end
local pos = ((n - i) % 8) + 1
c = d[c + 1][ p[pos][digit + 1] ]
end
elseif type(input) == "table" then
local n = #input
for i = n, 1, -1 do
local digit = input[i]
if type(digit) ~= "number" or digit < 0 or digit > 9 or digit ~= math.floor(digit) then
error("Invalid digit at position " .. i .. " in input table. Expected an integer 0–9.")
end
local pos = ((n - i) % 8) + 1
c = d[c + 1][ p[pos][digit + 1] ]
end
else
error("Input must be a string or a table of digits (0–9).")
end
return c == 0
end
----------------------------------------------------------------------
-- Append the Verhoeff check digit to the given number.
--
-- @param input (string|table) A number without the check digit (as a string or table)
-- @return (string|table) The input with the computed check digit appended (same format as input)
----------------------------------------------------------------------
function verhoeff.append(input)
local checkDigit = verhoeff.generate(input)
if type(input) == "string" then
return input .. tostring(checkDigit)
elseif type(input) == "table" then
local result = {}
for i = 1, #input do
result[i] = input[i]
end
result[#result + 1] = checkDigit
return result
else
error("Input must be a string or a table of digits (0–9).")
end
end
return verhoeff
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