How to check an EAN13 barcode's CRC

An EAN13 barcode has a built-in checksum to help cash registers discover damaged barcodes. You can easily check these checksums by hand.

Standard	Digit positions
EAN-8											N₁	N₂	N₃	N₄	N₅	N₆	N₇	N₈
EAN-12							N₁	N₂	N₃	N₄	N₅	N₆	N₇	N₈	N₉	N₁₀	N₁₁	N₁₂
EAN-13						N₁	N₂	N₃	N₄	N₅	N₆	N₇	N₈	N₉	N₁₀	N₁₁	N₁₂	N₁₃
EAN-14					N₁	N₂	N₃	N₄	N₅	N₆	N₇	N₈	N₉	N₁₀	N₁₁	N₁₂	N₁₃	N₁₄
SSCC	N₁	N₂	N₃	N₄	N₅	N₆	N₇	N₈	N₉	N₁₀	N₁₁	N₁₂	N₁₃	N₁₄	N₁₅	N₁₆	N₁₇	N₁₈
Step 1: Multiply value of each position by
	x3	x1	x3	x1	x3	x1	x3	x1	x3	x1	x3	x1	x3	x1	x3	x1	x3
Step 2: Add results together to create sum
Step 3: Subtract the sum from nearest equal or higher multiple of ten = *Check Digit*

The following table gives an example to illustrate how a Check Digit is calculated:

Pos	N₁	N₂	N₃	N₄	N₅	N₆	N₇	N₈	N₉	N₁₀	N₁₁	N₁₂	N₁₃
Number *without* Check Digit	1	2	3	4	5	6	7	8	9	1	2	3	-
Step 1: Multiply	x	x	x	x	x	x	x	x	x	x	x	x	-
by	1	3	1	3	1	3	1	3	1	3	1	3	-
Step 2: Add results	=	=	=	=	=	=	=	=	=	=	=	=	-
to create *sum*	1	6	3	12	5	18	7	24	9	3	2	9	= 91
Step 3: Subtract the sum from nearest equal or higher multiple of ten = 100-99 = 1
Number *with* Check Digit	1	2	3	4	5	6	7	8	9	1	2	3	1

My PHP code to check the CRC code:

function ean13_check_digit($digits){
   $digits=preg_split("//",$digits,-1,PREG_SPLIT_NO_EMPTY);
   $a=$b=0;
   for($i=0;$i&lt;6;$i++){
      $a+=(int)array_shift($digits);
      $b+=(int)array_shift($digits);
   }
   $total=($a*1)+($b*3);
   $nextten=ceil($total/10)*10;
   return $nextten-$total==array_shift($digits);
}
 
 
echo ean13_check_digit('1234567891231')?"good":"wrong";
echo ean13_check_digit('1234567891232')?"good":"wrong";
echo ean13_check_digit('1234567891233')?"good":"wrong";
echo ean13_check_digit('1234567891234')?"good":"wrong";
echo ean13_check_digit('1234567891235')?"good":"wrong";
echo ean13_check_digit('1234567891236')?"good":"wrong";
echo ean13_check_digit('1234567891237')?"good":"wrong";

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How to check an EAN13 barcode’s CRC

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