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annotate libutil/iccid_luhn.c @ 76:526193acfb3f

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doc/GrcardSIM2-WEKI-file: update with knowledge from doc/vendor/grcard2-person-script
author Mychaela Falconia <falcon@freecalypso.org>
date Fri, 09 Apr 2021 02:01:47 +0000
parents 34bbb0585cab
children
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34bbb0585cab libutil: import from previous fc-pcsc-tools version
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1 /*
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2 * This module implements a function for computing the Luhn check digit
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3 * for ICCIDs that follow the 18+1 convention.
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4 */
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5
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6 #include <sys/types.h>
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7
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8 compute_iccid_luhn(digits)
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9 u_char *digits;
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10 {
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11 int i, dig, sum;
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12
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13 sum = 0;
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14 for (i = 0; i < 18; i++) {
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15 dig = digits[i];
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16 if (i & 1) {
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17 dig *= 2;
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18 if (dig > 9)
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19 dig -= 9;
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20 }
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21 sum += dig;
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22 }
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23 dig = sum % 10;
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24 if (dig)
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25 dig = 10 - dig;
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26 return dig;
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27 }