function checkrequired(){var vendors=new Array();if((isbn=correctisbn())==false){document.getElementById("isbnform").isbnno.focus();return false;}
if(isbn>=9780000000000&&isbn<=9785999999999||isbn>=9787000000000&&isbn<=9787999999999){countrylength=4;}
else if(isbn>=9788000000000&&isbn<=9789499999999||isbn>=9791000000000&&isbn<=9791099999999){countrylength=5;}
else if(isbn>=9786000000000&&isbn<=9786499999999||isbn>=9789500000000&&isbn<=9789899999999){countrylength=6;}
else if(isbn>=9789900000000&&isbn<=9789989999999){countrylength=7;}
else if(isbn>=9789990000000&&isbn<=9789999999999){countrylength=8;}
else{countrylength=10;}
countrycode=parseFloat(isbn.substring(0,countrylength));vendors=checkvendor(countrycode,isbn.substring(countrylength,12));vendorlength=vendors[0];vendorcode=isbn.substring(countrylength,countrylength+vendorlength);if(isbn.substring(0,3)=="978"){returnisbn10=checkISBN10(isbn.substring(3,12));}
else{returnisbn10="N/A";}
if(vendorlength!=-1){countrycode=""+countrycode;if(countrycode.substring(0,3)=="979"){returnisbn13="979-"+countrycode.substring(3,countrylength)+"-"+vendorcode+"-"+isbn.substring(countrylength+vendorlength,12)+"-"+isbn.substring(12,13);}else{returnisbn10=countrycode.substring(3,countrylength)+"-"+vendorcode+"-"+returnisbn10.substring(countrylength+vendorlength-3,9)+"-"+returnisbn10.substring(9,10);returnisbn13="978-"+countrycode.substring(3,countrylength)+"-"+vendorcode+"-"+isbn.substring(countrylength+vendorlength,12)+"-"+isbn.substring(12,13);}}
else{returnisbn13=isbn;}
document.getElementById("isbnform").isbnno.value="";document.getElementById("isbnform").isbnno10.value=returnisbn10;document.getElementById("isbnform").isbnno13.value=returnisbn13;document.getElementById("isbnform").isbnregion.value=vendors[1];document.getElementById("isbnform").isbnno.focus();return false;}
function correctisbn(){isbn=document.getElementById("isbnform").isbnno.value.replace(/[- \.]/g,"");if(isbn.length==9||isbn.length==12){isbn=isbn+" ";}
if(isbn.length!=10&&isbn.length!=13){alert("Invalid ISBN number.");document.getElementById("isbnform").isbnno.focus();return false;}
if((isbn.length==13&&isbn.substring(0,3)!="978"&&isbn.substring(0,3)!="979")||(isbn.length==10&&isNaN(isbn.substring(0,9)))||(isbn.length==13&&isNaN(isbn))){alert("Invalid ISBN number.");document.getElementById("isbnform").isbnno.focus();return false;}
if(isbn.length==10){isbn="978"+isbn;}
return checkISBN13(isbn.substring(0,12))}
function checkISBN10(code){code=(code+'').replace(/[-\s]/g,'');if(!/^\d{9}[\dxX]?$/.test(code))return;var i=0,c=0;for(;i<9;)
c+=code.charAt(i++)*i;c%=11;if(c==10)c='X';if(code.length==9)return code+c;return c==(i=code.charAt(9))||c=='X'&&i=='x';}
function checkISBN13(code){code=(code+'').replace(/[-\s]/g,'');if(!/^\d{12,13}$/.test(code))return;var i=1,c=0;for(;i<12;i+=2)
c+=Math.floor(code.charAt(i));for(c*=3,i=0;i<12;i+=2)
c+=Math.floor(code.charAt(i));c=(220-c)%10;if(code.length==12)return code+c;return c==code.charAt(12);}
function log10(arg){return Math.log(arg)/Math.LN10;}