Fuzzy searching

gistfile1.c

#include <stdlib.h>
#include <string.h>
#include <limits.h>
#include <stdio.h>

const char *
bitap_fuzzy_search (const char *text, const char *pattern, int errors)
{
  const char *result = NULL;
  int m = strlen (pattern);
  unsigned long *R;
  unsigned long bitmasks[CHAR_MAX + 1];
  int i, d;

  if (pattern[0] == '\0') return text;
  if (m > 31) return "The pattern is too long!";

  /* Initialize the bit array R */
  R = malloc ((errors + 1) * sizeof (*R));
  for (i = 0; i <= errors; ++i)
    R[i] = ~1;

  /* Initialize the pattern bitmaskss */
  for (i = 0; i <= CHAR_MAX; ++i)
    bitmasks[i] = ~0;
  for (i = 0; i < m; ++i)
    bitmasks[pattern[i]] &= ~(1UL << i);

  for (i = 0; text[i] != '\0'; ++i)
    {
      /* Update the bit arrays */
      unsigned long old_Rd1 = R[0];

      R[0] |= bitmasks[text[i]];
      R[0] <<= 1;

      for (d = 1; d <= errors; ++d)
        {
          unsigned long tmp = R[d];
          /* Substitution is all we care about */
          R[d] = (old_Rd1 & (R[d] | bitmasks[text[i]])) << 1;
          old_Rd1 = tmp;
        }

    if (0 == (R[errors] & (1UL << m)))
      {
        result = (text + i - m) + 1;
        break;
      }
    }

  free (R);
  return result;
}

int
main (int argc, char *argv[])
{
  if (argv[1] && argv[2])
    printf ("%s\n", bitap_fuzzy_search(argv[1], argv[2], argv[3] ? atoi (argv[3]) : 3));
  else
    printf ("Usage: %s TEXT PATTERN [ERRORS]\n", argv[0]);
}