+++ /dev/null
-/*
- * decompress.h
- *
- * Functions useful for decompression, mainly bitstreams.
- */
-
-#ifndef _WIMLIB_DECOMP_H
-#define _WIMLIB_DECOMP_H
-
-#include "util.h"
-#include "endianness.h"
-
-/* Must be at least 32 bits. */
-typedef unsigned long input_bitbuf_t;
-
-/* Structure to encapsulate a block of in-memory data that is being interpreted
- * as a stream of bits.
- *
- * This is geared specifically towards the XPRESS and LZX compression formats
- * with regards to the actual ordering the bits within the byte sequence. */
-struct input_bitstream {
-
- /* A variable of length at least 32 bits that is used to hold bits that
- * have been read from the stream. The bits are ordered from high-order
- * to low-order, and the next bit is always the high-order bit. */
- input_bitbuf_t bitbuf;
-
- /* Pointer to the next byte to be retrieved from the input. */
- const u8 *data;
-
- /* Number of bits in @bitbuf that are valid. */
- unsigned bitsleft;
-
- /* Number of words of data that are left. */
- unsigned data_bytes_left;
-};
-
-/* Initializes a bitstream to receive its input from @data. */
-static inline void init_input_bitstream(struct input_bitstream *istream,
- const void *data, unsigned num_data_bytes)
-{
- istream->bitbuf = 0;
- istream->bitsleft = 0;
- istream->data = data;
- istream->data_bytes_left = num_data_bytes;
-}
-
-/* Ensures that the bit buffer variable for the bitstream contains @num_bits
- * bits.
- *
- * If there are at least @num_bits bits remaining in the bitstream, 0 is
- * returned. Otherwise, -1 is returned. */
-static inline int bitstream_ensure_bits(struct input_bitstream *istream,
- unsigned num_bits)
-{
- wimlib_assert2(num_bits <= 16);
-
- int ret = 0;
-
- /* Unfortunately this needs to be different for the different
- * compression types. LZX requires reading no more than the number of
- * bits needed, otherwise the end of the compressed data may be overrun.
- * XPRESS, on the other hand, requires that we always return with at
- * least 16 bits in the buffer, even if fewer are requested. This is
- * important because this may change the location of a literal byte
- * read with bitstream_read_byte(). */
-#ifdef XPRESS_DECOMP
- if (istream->bitsleft < 16) {
-#else
- if (istream->bitsleft < num_bits) {
-#endif
- if (istream->data_bytes_left >= 2) {
- unsigned shift = sizeof(input_bitbuf_t) * 8 - 16 -
- istream->bitsleft;
- istream->bitbuf |= (input_bitbuf_t)le16_to_cpu(
- *(u16*)istream->data) << shift;
- istream->data += 2;
- istream->bitsleft += 16;
- istream->data_bytes_left -= 2;
- } else {
- ret = -1;
- }
- }
- wimlib_assert2(ret != 0 || istream->bitsleft >= num_bits);
- return ret;
-}
-
-/* Returns the next @num_bits bits in the buffer variable, which must contain at
- * least @num_bits bits, for the bitstream. */
-static inline unsigned
-bitstream_peek_bits(const struct input_bitstream *istream, unsigned num_bits)
-{
- wimlib_assert2(istream->bitsleft >= num_bits);
- int ret;
- if (num_bits == 0)
- ret = 0;
- else
- ret = istream->bitbuf >> (sizeof(input_bitbuf_t) * 8 - num_bits);
- return ret;
-}
-
-/* Removes @num_bits bits from the buffer variable, which must contain at least
- * @num_bits bits, for the bitstream. */
-static inline void bitstream_remove_bits(struct input_bitstream *istream,
- unsigned num_bits)
-{
- wimlib_assert2(istream->bitsleft >= num_bits);
- istream->bitbuf <<= num_bits;
- istream->bitsleft -= num_bits;
-}
-
-/* Reads @num_bits bits from the input bitstream. @num_bits must be 16 or fewer.
- * On success, returns 0 and returns the requested bits in @n. If there are
- * fewer than @num_bits remaining in the bitstream, -1 is returned. */
-static inline int bitstream_read_bits(struct input_bitstream *istream,
- unsigned num_bits, unsigned *n)
-{
- wimlib_assert2(num_bits <= 16);
- int ret = bitstream_ensure_bits(istream, num_bits);
- if (ret == 0) {
- *n = bitstream_peek_bits(istream, num_bits);
- bitstream_remove_bits(istream, num_bits);
- } else {
- ERROR("bitstream_read_bits(): Input buffer exhausted");
- }
- return ret;
-}
-
-/* In the XPRESS format there can be literal bytes embedded in the bitstream.
- * These bytes are basically separate from the bitstream, as they come AFTER the
- * bits that are currently in the buffer variable (based on reading 16 bits at a
- * time), even though the buffer variable may not be empty.
- *
- * This function returns the next such literal byte, or -1 if there are no more.
- */
-static inline int bitstream_read_byte(struct input_bitstream *istream)
-{
- wimlib_assert2(istream->bitsleft < 32);
- int ret;
-
- if (istream->data_bytes_left == 0) {
- ERROR("bitstream_read_byte(): Input buffer exhausted");
- ret = -1;
- } else {
- istream->data_bytes_left--;
- ret = *istream->data++;
- }
- return ret;
-}
-
-/* Reads @num_bits bits from the buffer variable for a bistream without checking
- * to see if that many bits are in the buffer or not. */
-static inline unsigned
-bitstream_read_bits_nocheck(struct input_bitstream *istream, unsigned num_bits)
-{
- unsigned n = bitstream_peek_bits(istream, num_bits);
- bitstream_remove_bits(istream, num_bits);
- return n;
-}
-
-extern int read_huffsym_near_end_of_input(struct input_bitstream *istream,
- const u16 decode_table[],
- const u8 lens[],
- unsigned num_syms,
- unsigned table_bits,
- unsigned *n);
-
-/*
- * Reads a Huffman-encoded symbol from a bitstream.
- *
- * This function may be called hundreds of millions of times when extracting a
- * large WIM file. I'm not sure it could be made much faster that it is,
- * especially since there isn't enough time to make a big table that allows
- * decoding multiple symbols per lookup. But if extracting files to a hard
- * disk, the I/O will be the bottleneck anyway.
- *
- * @buf: The input buffer from which the symbol will be read.
- * @decode_table: The fast Huffman decoding table for the Huffman tree.
- * @lengths: The table that gives the length of the code for each
- * symbol.
- * @num_symbols: The number of symbols in the Huffman code.
- * @table_bits: Huffman codes this length or less can be looked up
- * directory in the decode_table, as the
- * decode_table contains 2**table_bits entries.
- */
-static inline int read_huffsym(struct input_bitstream *istream,
- const u16 decode_table[],
- const u8 lens[],
- unsigned num_syms,
- unsigned table_bits,
- unsigned *n,
- unsigned max_codeword_len)
-{
- int ret;
-
- /* In the most common case, there are at least max_codeword_len bits
- * remaining in the stream. */
- if (bitstream_ensure_bits(istream, max_codeword_len) == 0) {
-
- /* Use the next table_bits of the input as an index into the
- * decode_table. */
- u16 key_bits = bitstream_peek_bits(istream, table_bits);
-
- u16 sym = decode_table[key_bits];
-
- /* If the entry in the decode table is not a valid symbol, it is
- * the offset of the root of its Huffman subtree. */
- if (sym >= num_syms) {
- bitstream_remove_bits(istream, table_bits);
- do {
- key_bits = sym + bitstream_peek_bits(istream, 1);
- bitstream_remove_bits(istream, 1);
-
- wimlib_assert2(key_bits < num_syms * 2 +
- (1 << table_bits));
- } while ((sym = decode_table[key_bits]) >= num_syms);
- } else {
- wimlib_assert2(lens[sym] <= table_bits);
- bitstream_remove_bits(istream, lens[sym]);
- }
- *n = sym;
- ret = 0;
- } else {
- /* Otherwise, we must be careful to use only the bits that are
- * actually remaining. */
- ret = read_huffsym_near_end_of_input(istream, decode_table,
- lens, num_syms,
- table_bits, n);
- }
- return ret;
-}
-
-extern int make_huffman_decode_table(u16 decode_table[], unsigned num_syms,
- unsigned num_bits, const u8 lengths[],
- unsigned max_codeword_len);
-
-#endif /* _WIMLIB_DECOMP_H */
git://wimlib.net / wimlib / blobdiff