approximate string matching with bitwise

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

const char *search(const char *text, const char *pattern)
{
 int num = strlen(pattern),i=0;
 unsigned long X;
 unsigned long mask[CHAR_MAX+1];

  if (pattern[0] == '\0')
   return text;

  if (num > 31)
   return "The pattern is too long!";

  X = ~1;

  for (i=0; i <= CHAR_MAX; ++i)
   mask[i] = ~0;

  for (i=0; i < num; ++i)
   mask[pattern[i]] &= ~(1UL << i);

  for (i=0; text[i] != '\0'; ++i)
  {
   X |= mask[text[i]];
   X <<= 1;
   if (!(X & (1UL << num)))
    return (text + i - num) + 1;
  }

 return NULL;
}


int main()
{
 puts(search("ola cara","macaco"));
 puts(search("ola cara","cara"));
 puts(search("ola cara","la"));

 return 0;
}