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https://github.com/ZDoom/gzdoom.git
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403 lines
10 KiB
C++
403 lines
10 KiB
C++
/*
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gunzip.c by Pasi Ojala, a1bert@iki.fi
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http://www.iki.fi/a1bert/
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A hopefully easier to understand guide to GZip
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(deflate) decompression routine than the GZip
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source code.
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*/
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/*----------------------------------------------------------------------*/
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#include <stdlib.h>
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#include "ancientzip.h"
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/****************************************************************
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Bit-I/O variables and routines/macros
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These routines work in the bit level because the target
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environment does not have a barrel shifter. Trying to
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handle several bits at once would've only made the code
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slower.
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If the environment supports multi-bit shifts, you should
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write these routines again (see e.g. the GZIP sources).
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[RH] Since the target environment is not a C64, I did as
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suggested and rewrote these using zlib as a reference.
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****************************************************************/
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#define READBYTE(c) \
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do { \
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c = 0; \
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if (InLeft) { \
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InLeft--; \
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if (bs < be) \
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c = ReadBuf[bs++]; \
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else { \
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be = In->Read(&ReadBuf, sizeof(ReadBuf)); \
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c = ReadBuf[0]; \
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bs = 1; \
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} \
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} \
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} while (0)
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/* Get a byte of input into the bit accumulator. */
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#define PULLBYTE() \
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do { \
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unsigned char next; \
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READBYTE(next); \
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Hold += (unsigned int)(next) << Bits; \
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Bits += 8; \
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} while (0)
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/* Assure that there are at least n bits in the bit accumulator. */
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#define NEEDBITS(n) \
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do { \
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while (Bits < (unsigned)(n)) \
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PULLBYTE(); \
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} while (0)
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/* Return the low n bits of the bit accumulator (n < 16) */
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#define BITS(n) \
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((unsigned)Hold & ((1U << (n)) - 1))
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/* Remove n bits from the bit accumulator */
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#define DROPBITS(n) \
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do { \
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Hold >>= (n); \
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Bits -= (unsigned)(n); \
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} while (0)
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#define READBITS(c, a) \
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do { \
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NEEDBITS(a); \
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c = BITS(a); \
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DROPBITS(a); \
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} while (0)
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/****************************************************************
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Shannon-Fano tree routines
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****************************************************************/
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static const unsigned char BitReverse4[] = {
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0x00, 0x08, 0x04, 0x0c, 0x02, 0x0a, 0x06, 0x0e,
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0x01, 0x09, 0x05, 0x0d, 0x03, 0x0b, 0x07, 0x0f
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};
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#define FIRST_BIT_LEN 8
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#define REST_BIT_LEN 4
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void FZipExploder::InsertCode(TArray<HuffNode> &decoder, unsigned int pos, int bits, unsigned short code, int len, unsigned char value)
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{
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assert(len > 0);
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unsigned int node = pos + (code & ((1 << bits) - 1));
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if (len > bits)
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{ // This code uses more bits than this level has room for. Store the bottom bits
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// in this table, then proceed to the next one.
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unsigned int child = decoder[node].ChildTable;
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if (child == 0)
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{ // Need to create child table.
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child = InitTable(decoder, 1 << REST_BIT_LEN);
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decoder[node].ChildTable = child;
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decoder[node].Length = bits;
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decoder[node].Value = 0;
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}
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else
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{
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assert(decoder[node].Length == bits);
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assert(decoder[node].Value == 0);
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}
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InsertCode(decoder, child, REST_BIT_LEN, code >> bits, len - bits, value);
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}
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else
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{ // If this code uses fewer bits than this level of the table, it is
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// inserted repeatedly for each value that matches it at its lower
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// bits.
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for (int i = 1 << (bits - len); --i >= 0; node += 1 << len)
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{
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decoder[node].Length = len;
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decoder[node].Value = value;
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assert(decoder[node].ChildTable == 0);
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}
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}
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}
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unsigned int FZipExploder::InitTable(TArray<HuffNode> &decoder, int numspots)
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{
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unsigned int start = decoder.Size();
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decoder.Reserve(numspots);
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memset(&decoder[start], 0, sizeof(HuffNode)*numspots);
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return start;
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}
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int STACK_ARGS FZipExploder::buildercmp(const void *a, const void *b)
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{
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const TableBuilder *v1 = (const TableBuilder *)a;
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const TableBuilder *v2 = (const TableBuilder *)b;
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int d = v1->Length - v2->Length;
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if (d == 0) {
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d = v1->Value - v2->Value;
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}
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return d;
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}
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int FZipExploder::BuildDecoder(TArray<HuffNode> &decoder, TableBuilder *values, int numvals)
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{
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int i;
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qsort(values, numvals, sizeof(*values), buildercmp);
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// Generate the Shannon-Fano tree:
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unsigned short code = 0;
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unsigned short code_increment = 0;
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unsigned short last_bit_length = 0;
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for (i = numvals - 1; i >= 0; --i)
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{
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code += code_increment;
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if (values[i].Length != last_bit_length)
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{
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last_bit_length = values[i].Length;
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code_increment = 1 << (16 - last_bit_length);
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}
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// Reverse the order of the bits in the code before storing it.
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values[i].Code = BitReverse4[code >> 12] |
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(BitReverse4[(code >> 8) & 0xf] << 4) |
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(BitReverse4[(code >> 4) & 0xf] << 8) |
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(BitReverse4[code & 0xf] << 12);
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}
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// Insert each code into the hierarchical table. The top level is FIRST_BIT_LEN bits,
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// and the other levels are REST_BIT_LEN bits. If a code does not completely fill
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// a level, every permutation for the remaining bits is filled in to
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// match this one.
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InitTable(decoder, 1 << FIRST_BIT_LEN); // Set up the top level.
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for (i = 0; i < numvals; ++i)
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{
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InsertCode(decoder, 0, FIRST_BIT_LEN, values[i].Code, values[i].Length, values[i].Value);
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}
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return 0;
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}
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int FZipExploder::DecodeSFValue(const TArray<HuffNode> &decoder)
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{
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unsigned int bits = FIRST_BIT_LEN, table = 0, code;
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const HuffNode *pos;
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do
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{
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NEEDBITS(bits);
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code = BITS(bits);
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bits = REST_BIT_LEN;
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pos = &decoder[table + code];
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DROPBITS(pos->Length);
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table = pos->ChildTable;
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}
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while (table != 0);
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return pos->Value;
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}
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int FZipExploder::DecodeSF(TArray<HuffNode> &decoder, int numvals)
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{
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TableBuilder builder[256];
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unsigned char a, c;
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int i, n, v = 0;
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READBYTE(c);
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n = c + 1;
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for (i = 0; i < n; i++) {
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int nv, bl;
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READBYTE(a);
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nv = ((a >> 4) & 15) + 1;
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bl = (a & 15) + 1;
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while (nv--) {
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builder[v].Length = bl;
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builder[v].Value = v;
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v++;
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}
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}
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if (v != numvals)
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return 1; /* bad table */
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return BuildDecoder(decoder, builder, v);
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}
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int FZipExploder::Explode(unsigned char *out, unsigned int outsize,
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FileReader *in, unsigned int insize,
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int flags)
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{
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int c, i, minMatchLen = 3, len, dist;
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int lowDistanceBits;
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unsigned int bIdx = 0;
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Hold = 0;
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Bits = 0;
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In = in;
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InLeft = insize;
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bs = be = 0;
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if ((flags & 4)) {
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/* 3 trees: literals, lengths, distance top 6 */
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minMatchLen = 3;
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if (DecodeSF(LiteralDecoder, 256))
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return 1;
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} else {
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/* 2 trees: lengths, distance top 6 */
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minMatchLen = 2;
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}
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if (DecodeSF(LengthDecoder, 64))
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return 1;
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if (DecodeSF(DistanceDecoder, 64))
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return 1;
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lowDistanceBits = (flags & 2) ? /* 8k dictionary */ 7 : /* 4k dictionary */ 6;
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while (bIdx < outsize)
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{
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READBITS(c, 1);
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if (c) {
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/* literal data */
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if ((flags & 4)) {
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c = DecodeSFValue(LiteralDecoder);
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} else {
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READBITS(c, 8);
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}
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out[bIdx++] = c;
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} else {
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READBITS(dist, lowDistanceBits);
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c = DecodeSFValue(DistanceDecoder);
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dist |= (c << lowDistanceBits);
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len = DecodeSFValue(LengthDecoder);
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if (len == 63) {
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READBITS(c, 8);
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len += c;
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}
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len += minMatchLen;
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dist++;
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if (bIdx + len > outsize) {
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throw CExplosionError("Not enough output space");
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}
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if ((unsigned int)dist > bIdx) {
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/* Anything before the first input byte is zero. */
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int zeros = dist - bIdx;
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if (len < zeros)
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zeros = len;
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for(i = zeros; i; i--)
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out[bIdx++] = 0;
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len -= zeros;
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}
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for(i = len; i; i--, bIdx++) {
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out[bIdx] = out[bIdx - dist];
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}
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}
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}
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return 0;
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}
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/* HSIZE is defined as 2^13 (8192) in unzip.h */
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#define HSIZE 8192
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#define BOGUSCODE 256
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#define CODE_MASK (HSIZE - 1) /* 0x1fff (lower bits are parent's index) */
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#define FREE_CODE HSIZE /* 0x2000 (code is unused or was cleared) */
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#define HAS_CHILD (HSIZE << 1) /* 0x4000 (code has a child--do not clear) */
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int ShrinkLoop(unsigned char *out, unsigned int outsize,
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FileReader *In, unsigned int InLeft)
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{
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unsigned char ReadBuf[256];
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unsigned short Parent[HSIZE];
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unsigned char Value[HSIZE], Stack[HSIZE];
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unsigned char *newstr;
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int len;
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int KwKwK, codesize = 9; /* start at 9 bits/code */
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int code, oldcode, freecode, curcode;
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unsigned int Bits = 0, Hold = 0;
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unsigned int size = 0;
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unsigned int bs = 0, be = 0;
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freecode = BOGUSCODE;
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for (code = 0; code < BOGUSCODE; code++)
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{
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Value[code] = code;
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Parent[code] = BOGUSCODE;
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}
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for (code = BOGUSCODE+1; code < HSIZE; code++)
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Parent[code] = FREE_CODE;
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READBITS(oldcode, codesize);
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if (size < outsize) {
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out[size++] = oldcode;
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}
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while (size < outsize)
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{
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READBITS(code, codesize);
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if (code == BOGUSCODE) { /* possible to have consecutive escapes? */
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READBITS(code, codesize);
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if (code == 1) {
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codesize++;
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} else if (code == 2) {
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/* clear leafs (nodes with no children) */
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/* first loop: mark each parent as such */
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for (code = BOGUSCODE+1; code < HSIZE; ++code) {
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curcode = (Parent[code] & CODE_MASK);
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if (curcode > BOGUSCODE)
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Parent[curcode] |= HAS_CHILD; /* set parent's child-bit */
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}
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/* second loop: clear all nodes *not* marked as parents; reset flag bits */
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for (code = BOGUSCODE+1; code < HSIZE; ++code) {
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if (Parent[code] & HAS_CHILD) { /* just clear child-bit */
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Parent[code] &= ~HAS_CHILD;
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} else { /* leaf: lose it */
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Parent[code] = FREE_CODE;
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}
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}
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freecode = BOGUSCODE;
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}
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continue;
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}
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newstr = &Stack[HSIZE-1];
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curcode = code;
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if (Parent[curcode] == FREE_CODE) {
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KwKwK = 1;
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newstr--; /* last character will be same as first character */
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curcode = oldcode;
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len = 1;
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} else {
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KwKwK = 0;
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len = 0;
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}
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do {
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*newstr-- = Value[curcode];
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len++;
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curcode = (Parent[curcode] & CODE_MASK);
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} while (curcode != BOGUSCODE);
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newstr++;
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if (KwKwK) {
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Stack[HSIZE-1] = *newstr;
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}
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do {
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freecode++;
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} while (Parent[freecode] != FREE_CODE);
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Parent[freecode] = oldcode;
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Value[freecode] = *newstr;
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oldcode = code;
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while (len--) {
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out[size++] = *newstr++;
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}
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}
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return 0;
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}
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