/*
 * Copyright (c) 1995, 1996 Gunther Schadow.  All rights reserved.
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 * 
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 * 
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
 */

#include "pg_config.h"

IDENT("@(#) checkdigit.c (Gunther Schadow) 12/19/96");

#include <ctype.h>

/*
 * A simple check digit method used by HP CareVue as their M10 or
 * M11 algorithm (n = 10 or 11 respectively).
 */
int
cdmod(const char *id, int n)
{
  int S_e = 0;
  int S_o = 0;

  const char *p = id;

  if(p == NULL) return 0;

  /* skip leading text */
  while(*p != 0 && !isdigit(*p)) p++;

  /* goto end of digit string */
  while(isdigit(*p)) p++;
  
  /* now go back again, adding and stop when the leading text or
     the beginning of the string is reached */
  while(TRUE)
    {
      p--;
      if(p < id || !isdigit(*p)) break;
      S_o += ( *p & ~'0' ); 
      p--;
      if(p < id || !isdigit(*p)) break;
      S_e += ( *p & ~'0' );
    }

  return ( 2 * S_o + S_e ) % n;
}

/* This is the standard HL7 M10 algorithm
 */
int
cdM10(unsigned long x)
{
  int odd = 0, even = 0, sum = 0;

  while(x != 0)
    {
      odd = odd * 10 + x % 10;
      x = x / 10uL;
      if(x == 0) break;
      even = even * 10 + x % 10;
      x = x / 10uL;
    }
  
  odd = odd * 2;
  
  while(odd != 0 || even != 0)
    {
      sum = sum + odd % 10 + even % 10;
      odd = odd / 10;
      even = even / 10;
    }

  return (10 - (sum % 10)) % 10;
}