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maketbl.c

/*$Source: /usr/home/dhesi/zoo/RCS/maketbl.c,v $*/
/*$Id: maketbl.c,v 1.8 91/07/09 01:39:52 dhesi Exp $*/
/***********************************************************
      maketbl.c -- make table for decoding

Adapted from "ar" archiver written by Haruhiko Okumura.
***********************************************************/
#include "options.h"
#include "zoo.h"
#include "ar.h"
#include "lzh.h"

extern void prterror();

void make_table(nchar, bitlen, tablebits, table)
int nchar;
uchar bitlen[];
int tablebits;
ushort table[];
{
      ushort count[17], weight[17], start[18], *p;
      uint i, k, len, ch, jutbits, avail, nextcode, mask;

      for (i = 1; i <= 16; i++) count[i] = 0;
      for (i = 0; i < nchar; i++) count[bitlen[i]]++;

      start[1] = 0;
      for (i = 1; i <= 16; i++)
            start[i + 1] = start[i] + (count[i] << (16 - i));
      if (start[17] != (ushort)((unsigned) 1 << 16))
            prterror('f', "Bad decode table\n");

      jutbits = 16 - tablebits;
      for (i = 1; i <= tablebits; i++) {
            start[i] >>= jutbits;
            weight[i] = (unsigned) 1 << (tablebits - i);
      }
      while (i <= 16) {
         weight[i] = (unsigned) 1 << (16 - i);
         i++;
        }

      i = start[tablebits + 1] >> jutbits;
      if (i != (ushort)((unsigned) 1 << 16)) {
            k = 1 << tablebits;
            while (i != k) table[i++] = 0;
      }

      avail = nchar;
      mask = (unsigned) 1 << (15 - tablebits);
      for (ch = 0; ch < nchar; ch++) {
            if ((len = bitlen[ch]) == 0) continue;
            nextcode = start[len] + weight[len];
            if (len <= tablebits) {
                  for (i = start[len]; i < nextcode; i++) table[i] = ch;
            } else {
                  k = start[len];
                  p = &table[k >> jutbits];
                  i = len - tablebits;
                  while (i != 0) {
                        if (*p == 0) {
                              right[avail] = left[avail] = 0;
                              *p = avail++;
                        }
                        if (k & mask) p = &right[*p];
                        else          p = &left[*p];
                        k <<= 1;  i--;
                  }
                  *p = ch;
            }
            start[len] = nextcode;
      }
}

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