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/*********************************************************************** |
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** |
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** lzv.c -- an extremly fast compression/decompression-method |
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** |
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** Written by Hermann Vogt |
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** |
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** v 0.5 -- 00/04/10 fix unaligned access (Marc) |
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** v 0.4 -- 00/03/25 adapted for PApp by Marc Lehmann <pcg@goof.com> |
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** v 0.3 -- 94/03/08 aCembler version of rLZV built in. |
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** v 0.2 -- 94/03/04 Changes for usage with DouBle 0.2 built in. |
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** v 0.1 -- 94/03/01 Intensivly tested, removed all known bugs. |
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** v 0.0 -- 94/02/21 First Version. |
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** |
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** Copyright (c) 1994 Hermann Vogt. Redistribution of this file is |
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** permitted under the GNU Public Licence. |
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** |
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** The method presented here is faster and compresses better |
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** than lzrw1 and lzrw1-a. I named it lzv for "Lev-Zimpel-Vogt". |
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** It uses ideas introduced by Ross Williams in his algorithm lzrw1 |
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** [R. N. Williams (1991): "An Extremly Fast ZIV-Lempel Data |
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** Compression Algorithm", Proceedings IEEE Data Compression |
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** Conference, Snowbird, Utah, 362-371] and by Fiala and Green in their |
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** algorithm a1 [E. R. Fiala, D. H. Greene (1989): "Data Compression |
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** with Finite Windows", Communications of the ACM, 4, 490-505]. |
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** Because lzv differs strongly from both, I hope there will be no |
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** patent problems. The hashing-method has been stolen from Jean-loup |
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** Gailly's (patent free) gzip. |
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** |
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** KNOWN PROBLEMS: |
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** - My english is very bad. |
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** - Badly commented. (I hope this will be better in the next |
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** version.) |
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** - I'm not sure if lzv is free from patent problems. |
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** |
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***********************************************************************/ |
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|
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#define HSIZE 0x4000 |
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#define HMASK 0x3fff |
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#define HSHIFT 5 |
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|
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#define MLL 32 /* Maximum len of chain of literals */ |
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#define MML (8+256) /* Maximum len of match */ |
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#define MOFF 8191 /* Maximum offset */ |
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#define HSIZ 16384 /* Size of Hashtable */ |
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|
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/* ugly type names */ |
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|
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typedef unsigned char uch; |
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typedef unsigned short ush; |
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typedef unsigned int uit; |
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|
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#undef ONLY_64K /* 64k-max encoder is faster */ |
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/* but only veeeery slightly */ |
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|
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/* unconditionally aligning does not cost much much, so do it if unsure */ |
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#define align_ushort !defined(__i386) |
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|
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static int |
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wLZV1 (uch * in, uch * out, ush * heap, int len, int out_len) |
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{ |
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uit hval, op, ip, l_len, m_pos, m_off, m_len, maxlen; |
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ush *lzv1_htab = heap; |
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|
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maxlen = out_len; |
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hval = ((in[0] << 5) ^ in[1]) & (HSIZ - 1); |
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ip = op = l_len = 0; |
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|
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do |
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{ |
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hval = ((hval << 5) ^ in[ip + 2]) & (HSIZ - 1); |
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m_pos = lzv1_htab[hval]; |
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lzv1_htab[hval] = ip; |
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|
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#ifndef ONLY_64K |
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/* |
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* If you want to compress more than 64K, uncomment |
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* the following lines. |
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*/ |
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|
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m_pos = (ip & ~0xffff) + m_pos; |
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if (m_pos >= ip && m_pos >= 0x10000) |
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m_pos -= 0x10000; |
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#endif |
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|
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if (m_pos < ip |
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&& in[m_pos ] == in[ip ] |
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&& (m_off = ip - m_pos - 1) <= MOFF |
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&& ip + 4 < len |
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#if align_ushort |
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&& in[m_pos + 1] == in[ip + 1] |
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&& in[m_pos + 2] == in[ip + 2] |
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#else |
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&& *(ush *) (in + m_pos + 1) == *(ush *) (in + ip + 1) |
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#endif |
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) |
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{ |
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/* We have found a match */ |
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uit look = len - ip - 2; |
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if (look > MML) |
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look = MML; |
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m_len = 2; |
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|
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do |
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{ |
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m_len++; |
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} |
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while (m_len != look && in[ip + m_len] == in[m_pos + m_len]); |
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|
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if (op + 2 + l_len + 3 >= maxlen) |
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return 0; |
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|
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if (l_len != 0) |
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{ |
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out[op++] = (l_len - 1) << 3; |
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do |
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{ |
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out[op++] = in[ip - l_len--]; |
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} |
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while (l_len != 0); |
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} |
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|
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m_len -= 2; |
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|
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if (m_len <= 6) |
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{ |
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out[op++] = m_len | ((m_off >> 5) & 0xf8); |
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} |
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else |
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{ |
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out[op++] = 0x07 | ((m_off >> 5) & 0xf8); |
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out[op++] = m_len - 7; |
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} |
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|
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out[op++] = m_off & 0xff; |
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ip++; |
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hval = ((hval << 5) ^ in[ip + 2]) & (HSIZ - 1); |
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lzv1_htab[hval] = ip; |
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ip++; |
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|
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do |
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{ |
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hval = ((hval << 5) ^ in[ip + 2]) & (HSIZ - 1); |
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lzv1_htab[hval] = ip; |
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ip++; |
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m_len--; |
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} |
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while (0 != m_len); |
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} |
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else |
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{ |
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/* No match found */ |
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ip++; |
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l_len++; |
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|
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if (MLL == l_len) |
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{ |
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if (op + 2 + MLL >= maxlen) |
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return 0; |
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|
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out[op++] = 0xf8; |
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|
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do |
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{ |
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out[op++] = in[ip - l_len--]; |
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} |
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while (l_len != 0); |
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} |
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} |
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} |
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while (ip < len); |
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|
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if (l_len != 0) |
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{ |
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if (op + l_len + 3 >= maxlen) |
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return 0; |
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|
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out[op++] = (l_len - 1) << 3; |
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|
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do |
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{ |
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out[op++] = in[ip - l_len--]; |
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} |
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while (l_len != 0); |
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} |
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return op; |
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} |
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|
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static int |
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rLZV1 (uch const *const in, uch * const out, int ilen, int len) |
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{ |
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register uit tbuf, c_len; |
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uch *const out_end = out + len; |
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register uch *op = out; |
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uch const *const in_end = in + ilen; |
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register uch const *ip = in; |
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|
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do |
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{ |
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tbuf = *ip++; |
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c_len = tbuf & 0x07; |
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|
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if (0 == c_len) |
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{ |
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c_len = (tbuf >> 3) + 1; |
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|
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/*if (op + c_len > out_end) /* too many checks... */ |
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/* return 0;*/ |
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|
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do |
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*op++ = *ip++; |
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while (--c_len); /* effic: memcpy()? */ |
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} |
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else |
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{ |
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register uch *m_pos; |
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|
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if (0x07 == c_len) |
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c_len = *ip++ + 7; |
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m_pos = op - 1 - (((uit) (tbuf & 0xf8) << 5) | *ip++); |
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|
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/* If we don't check this then we segfault (if in user |
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space) or leave process in uninteruptible state (if |
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in kernel) if the data is corrupt. */ |
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if (m_pos < out) |
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return 0; /* Compression error. */ |
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|
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/*if (op + c_len + 2 > out_end) /* too many checks */ |
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/* return 0;*/ |
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|
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*op++ = *m_pos++; |
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*op++ = *m_pos++; |
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|
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do |
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*op++ = *m_pos++; |
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while (--c_len); |
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} |
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} |
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while (op < out_end && ip < in_end); |
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|
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return op - out; |
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} |
