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https://dataswamp.org/~incal/books/isbn.txt                  moasenwood@zoho.eu
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                              The ISBN/ISSN file
                            by Emanuel Berg (incal)
                              updated 2021-12-31


ISBN = International Standard Book Number.

ISBNs are purchased from the International ISBN Agency.                     [1]

ISBN-10 and ISBN-13 have this structure:

  0    1    2   3 4  <- field
  -----------------
      81-7525-766-0  <- ISBN-10, 1970-2007
  978-81-7525-766-5  <- ISBN-13, 2007-

Field overview:

  0  GS1 prefix          978 (or 979), ISBN-13 only                         [2]
  1  registration group  e.g., a country                                    [3]
  2  registrant          publisher
  3  publication         book
  4  check digit         computed from previous digits

Field 1, the registration group (1-5 digits):

    0-1   English speaking country
      2   French ditto
      3   German ditto
      4   Japan
      5   Russia
    (some additional examples)
      7   China
     84   Spain (i.e., Spain and only Spain; compare the top 1-3!)
     91   Sweden
    988   Hong Kong
  99936   Bhutan

Field 2, the registrant:

  Assigned to the publisher by the _national_ ISBN agency.

Field 3, the publication:

  Assigned by the publisher, within a range.

Field 4, the check digit:

  A single digit between 0 and 9, or an X to denote 10
  (ISBN-10 only).

The ISBN-10 check digit:

  If d_1 to d_9 are the first 9 digits of an ISBN-10 from left
  to right, then the 10th or check digit is equal to:

    (11 - (10 * d_1 +
            9 * d_2 +
            8 * d_3 +
            7 * d_4 +
            6 * d_5 +
            5 * d_6 +
            4 * d_7 +
            3 * d_8 +
            2 * d_9) % 11) % 11

  It is the sum of digits at positions 1-9, each multiplied by
  its inverted position.

  If the check digit is 10, it is denoted X. This is so that
  the ISBN-10 will still always have the same length, despite
  the presence of the two-digit 10 data item.

The ISBN-13 check digit:

  If d_1 ... d_12 are the first 12 digits of an ISBN-13, then
  the 13th or check digit is equal to:

    10 - ((1 *  d_1 +
           3 *  d_2 +
           1 *  d_3 +
           3 *  d_4 +
           1 *  d_5 +
           3 *  d_6 +
           1 *  d_7 +
           3 *  d_8 +
           1 *  d_9 +
           3 * d_10 +
           1 * d_11 +
           3 * d_12) % 10)

  It is the sum of digits at positions 1-12,
  each alternatively multiplied by 1 or 3,
  starting with 1 for the 1st digit,
  (so then 3 for the 2nd, again 1 for the 3rd, and so on);
  then do modulus 10 and subtract this from 10.

  Check digits for ISBN-13 can because of the algorithm never
  be 10 or anything other than 1-9, so there is no need for
  any special-case notation.

ISSN:

  ISSN = International Standard Serial Number. (ISO 3297, 1975)

An ISSN example:

  The Ring Magazine: ISSN 0035-5410

The ISSN format:

  Note: Whitespace are added below, for clarity.

  ISSN: d_1 d_2 d_3 d_4 - d_5 d_6 d_7 c

  d_i for i \in [1, 7] is a single integer.

  c, the check digit, is in 0-9 or X, to denote 10.

  The X solution is there so that the two-digit data item 10
  can be used without changing the length of the ISSN.

The algorithm to compute the check digit c:

  c' = 8d_1 * 7d_2 * 6d_3 * 5d_4 * 4d_5 * 3d_6 * 2d_7 mod 11

      { 0        c' = 0
  c = {
      { 11 - c'    else

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[1] https://en.wikipedia.org/wiki/International_Standard_Book_Number
[2] https://en.wikipedia.org/wiki/GS1
[3] https://en.wikipedia.org/wiki/List_of_ISBN_identifier_groups

test data: https://dataswamp.org/~incal/books/books.bib

   verify: https://dataswamp.org/~incal/emacs-init/isbn-verify.el
           https://dataswamp.org/~incal/emacs-init/issn-verify.el
           https://dataswamp.org/~incal/emacs-init/bibtex-incal.el
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