check Isxn

-- This template is a copy of the ISXN validation code from [[Module:Citation/CS1]] -- which allows for validating ISBN, ISMN, and ISSN without invoking a citation template  local p = {}  --[[--------------------------< IS _ V A L I D _ I S X N >-----------------------------------------------------  ISBN-10 and ISSN validator code calculates checksum across all isbn/issn digits including the check digit. ISBN-13 is checked in check_isbn(). If the number is valid the result will be 0. Before calling this function, issbn/issn must be checked for length and stripped of dashes, spaces and other non-isxn characters.  ]]  local function is_valid_isxn (isxn_str, len) local temp = 0; isxn_str = { isxn_str:byte(1, len) };-- make a table of byte values '0' → 0x30 .. '9'  → 0x39, 'X' → 0x58 len = len+1;-- adjust to be a loop counter for i, v in ipairs( isxn_str ) do-- loop through all of the bytes and calculate the checksum if v == string.byte( "X" ) then-- if checkdigit is X (compares the byte value of 'X' which is 0x58) temp = temp + 10*( len - i );-- it represents 10 decimal else temp = temp + tonumber( string.char(v) )*(len-i); end end return temp % 11 == 0;-- returns true if calculation result is zero end   --[[--------------------------< IS _ V A L I D _ I S X N  _ 1 3 >----------------------------------------------  ISBN-13 and ISMN validator code calculates checksum across all 13 isbn/ismn digits including the check digit. If the number is valid, the result will be 0. Before calling this function, isbn-13/ismn must be checked for length and stripped of dashes, spaces and other non-isxn-13 characters.  ]]  local function is_valid_isxn_13 (isxn_str) local temp=0;  isxn_str = { isxn_str:byte(1, 13) };-- make a table of byte values '0' → 0x30 .. '9'  → 0x39 for i, v in ipairs( isxn_str ) do temp = temp + (3 - 2*(i % 2)) * tonumber( string.char(v) );-- multiply odd index digits by 1, even index digits by 3 and sum; includes check digit end return temp % 10 == 0;-- sum modulo 10 is zero when isbn-13/ismn is correct end  --[[--------------------------< C H E C K _ I S B N >------------------------------------------------------------  Determines whether an ISBN string is valid  ]]  local function check_isbn( isbn_str, error_string ) if nil ~= isbn_str:match("[^%s-0-9X]") then -- fail if isbn_str contains anything but digits, hyphens, or the uppercase X return error_string; end isbn_str = isbn_str:gsub( "-", "" ):gsub( " ", "" );-- remove hyphens and spaces local len = isbn_str:len();   if len ~= 10 and len ~= 13 then return error_string; end  if len == 10 then if isbn_str:match( "^%d*X?$" ) == nil then  return error_string;  end return is_valid_isxn(isbn_str, 10) and '' or error_string; else local temp = 0; if isbn_str:match( "^97[89]%d*$" ) == nil then -- isbn13 begins with 978 or 979; ismn begins with 979 return error_string;  end return is_valid_isxn_13 (isbn_str) and '' or error_string; end end  --[[--------------------------< C H E C K _ I S M N >------------------------------------------------------------  Determines whether an ISMN string is valid.  Similar to isbn-13, ismn is 13 digits begining 979-0-... and uses the same check digit calculations.  See http://www.ismn-international.org/download/Web_ISMN_Users_Manual_2008-6.pdf section 2, pages 9–12.  ]]  local function check_ismn (id, error_string) local text; local valid_ismn = true;  id=id:gsub( "[%s-–]", "" );-- strip spaces, hyphens, and endashes from the ismn  if 13 ~= id:len() or id:match( "^9790%d*$" ) == nil then-- ismn must be 13 digits and begin 9790 valid_ismn = false; else valid_ismn=is_valid_isxn_13 (id);-- validate ismn end  return valid_ismn and '' or error_string end  --[[--------------------------< I S S N >----------------------------------------------------------------------  Validate and format an issn.  This code fixes the case where an editor has included an ISSN in the citation but has separated the two groups of four digits with a space.  When that condition occurred, the resulting link looked like this:  |issn=0819 4327 gives: [http://www.worldcat.org/issn/0819 4327 0819 4327]  -- can't have spaces in an external link  This code now prevents that by inserting a hyphen at the issn midpoint.  It also validates the issn for length and makes sure that the checkdigit agrees with the calculated value.  Incorrect length (8 digits), characters other than 0-9 and X, or checkdigit / calculated value mismatch will all cause a check issn error message.  ]]  local function check_issn(id, error_string) local issn_copy = id;-- save a copy of unadulterated issn; use this version for display if issn does not validate local text; local valid_issn = true;  if not id:match ('^%d%d%d%d%-%d%d%d[%dX]$') then return error_string; end  id=id:gsub( "[%s-–]", "" );-- strip spaces, hyphens, and endashes from the issn  if 8 ~= id:len() or nil == id:match( "^%d*X?$" ) then-- validate the issn: 8 digits long, containing only 0-9 or X in the last position valid_issn=false;-- wrong length or improper character else valid_issn=is_valid_isxn(id, 8);-- validate issn end  return valid_issn and '' or error_string end   ------------------------------< E N T R Y   P O I N T S >--------------------------------------------------====  function p.check_isbn(frame) return check_isbn(frame.args[1] or frame:getParent().args[1], frame.args['error'] or frame:getParent().args['error'] or 'error') end  function p.check_ismn(frame) return check_ismn(frame.args[1] or frame:getParent().args[1], frame.args['error'] or frame:getParent().args['error'] or 'error') end  function p.check_issn(frame) return check_issn(frame.args[1] or frame:getParent().args[1], frame.args['error'] or frame:getParent().args['error'] or 'error') end  return p