strmatch

SFL
Version 2.10

`strmatch`

#include "sflstr.h"
int
strmatch (
    const char *string1,
    const char *string2)

Synopsis

Calculates a similarity index for the two strings. This is a value from 0 to 32767 with higher values indicating a closer match. The two strings are compared without regard for case. The algorithm was designed by Leif Svalgaard leif@ibm.net.

Source Code - (sflstr.c)

{
    static int
        name_weight [30] = {
            20, 15, 13, 11, 10, 9, 8, 8, 7, 7, 7, 6, 6, 6, 6,
             6,  5,  5,  5,  5, 5, 4, 4, 4, 4, 4, 4, 4, 4, 4
        };
    int
        comp_index,
        name_index,
        start_of_string,
        longest_so_far,
        substring_contribution,
        substring_length,
        compare_length,
        longest_length,
        length_difference,
        name_length,
        char_index,
        similarity_index,
        similarity_weight;
    char
        cur_name_char;

    ASSERT (string1);
    ASSERT (string2);

    name_length    = strlen (string1);
    compare_length = strlen (string2);
    if (name_length > compare_length)
      {
        length_difference = name_length - compare_length;
        longest_length    = name_length;
      }
    else
      {
        length_difference = compare_length - name_length;
        longest_length    = compare_length;
      }
    if (compare_length)
      {
        similarity_weight = 0;
        substring_contribution = 0;

        for (char_index = 0; char_index < name_length; char_index++)
          {
            start_of_string = char_index;
            cur_name_char   = (char) tolower (string1 [char_index]);
            longest_so_far  = 0;
            comp_index      = 0;

            while (comp_index < compare_length)
              {
                while ((comp_index < compare_length)
                &&     (tolower (string2 [comp_index]) != cur_name_char))
                    comp_index++;

                substring_length = 0;
                name_index = start_of_string;

                while ((comp_index < compare_length)
                &&     (tolower (string2 [comp_index])
                     == tolower (string1 [name_index])))
                  {
                    if (comp_index == name_index)
                        substring_contribution++;
                    comp_index++;
                    if (name_index < name_length)
                      {
                        name_index++;
                        substring_length++;
                      }
                  }
                substring_contribution += (substring_length + 1) * 3;
                if (longest_so_far < substring_length)
                    longest_so_far = substring_length;
              }
            similarity_weight += (substring_contribution
                                  + longest_so_far + 1) * 2;
            similarity_weight /= name_length + 1;
          }
        similarity_index  = (name_length < 30? name_weight [name_length]: 3)
                          * longest_length;
        similarity_index /= 10;
        similarity_index += 2 * length_difference / longest_length;
        similarity_index  = 100 * similarity_weight / similarity_index;
      }
    else
        similarity_index = 0;

    return (similarity_index);
}

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