/* Compression routines */

/* These use a pathetically simple encoding that takes advantage of the */
/* eighth bit on a char; if you are using an international character set, */
/* they may need substantial patching. */

#ifdef COMPRESS

#define BUFFER_LEN 16384        /* nice big buffer */

#define TOKEN_BIT 0x80          /* if on, it's a token */
#define TOKEN_MASK 0x7f         /* for stripping out token value */
#define NUM_TOKENS (128)
#define MAX_CHAR (128)

/* Top 128 bigrams in the CMU TinyMUD database as of 2/13/90 */
static const char *tokens[NUM_TOKENS] = {
  "e ", " t", "th", "he", "s ", " a", "ou", "in",
  "t ", " s", "er", "d ", "re", "an", "n ", " i",
  " o", "es", "st", "to", "or", "nd", "o ", "ar",
  "r ", ", ", "on", " b", "ea", "it", "u ", " w",
  "ng", "le", "is", "te", "en", "at", " c", "y ",
  "ro", " f", "oo", "al", ". ", "a ", " d", "ut",
  " h", "se", "nt", "ll", "g ", "yo", " l", " y",
  " p", "ve", "f ", "as", "om", "of", "ha", "ed",
  "h ", "hi", " r", "lo", "Yo", " m", "ne", "l ",
  "li", "de", "el", "ta", "wa", "ri", "ee", "ti",
  "no", "do", "Th", " e", "ck", "ur", "ow", "la",
  "ac", "et", "me", "il", " g", "ra", "co", "ch",
  "ma", "un", "so", "rt", "ai", "ce", "ic", "be",
  " n", "k ", "ge", "ot", "si", "pe", "tr", "wi",
  "e.", "ca", "rs", "ly", "ad", "we", "bo", "ho",
  "ir", "fo", "ke", "us", "m ", " T", "di", ".."
};

static char token_table[MAX_CHAR][MAX_CHAR];
static int table_initialized = 0;

static void init_compress (void)
{
  int i;
  int j;

  for (i = 0; i < MAX_CHAR; i++) {
    for (j = 0; j < MAX_CHAR; j++) {
      token_table[i][j] = 0;
    }
  }

  for (i = 0; i < NUM_TOKENS; i++) {
    token_table[tokens[i][0]][tokens[i][1]] = i | TOKEN_BIT;
  }

  table_initialized = 1;
}

static int compressed (const char *s)
{
  while (*s) {
    if (*s++ & TOKEN_BIT)
      return 1;
  }
  return 0;
}

const char *compress (const char *s)
{
  static char buf[BUFFER_LEN];
  char *to;
  char token;

  if (!table_initialized)
    init_compress ();

  if (compressed (s))
    return s;                   /* already compressed */

  /* tokenize the first characters */
  for (to = buf; s[0] && s[1]; to++) {
    if (token = token_table[s[0]][s[1]]) {
      *to = token;
      s += 2;
    } else {
      *to = s[0];
      s++;
    }
  }

  /* copy the last character (if any) and null */
  while (*to++ = *s++);

  return buf;
}

const char *uncompress (const char *s)
{
  static char buf[BUFFER_LEN];
  char *to;
  const char *token;

  for (to = buf; *s; s++) {
    if (*s & TOKEN_BIT) {
      token = tokens[*s & TOKEN_MASK];
      *to++ = *token++;
      *to++ = *token;
    } else {
      *to++ = *s;
    }
  }

  *to++ = *s;

  return buf;
}

#endif /* COMPRESS */