From: Eric Biggers Date: Wed, 6 Aug 2014 03:26:38 +0000 (-0500) Subject: LZX decompression: Cleanup X-Git-Tag: v1.7.1~6 X-Git-Url: https://wimlib.net/git/?p=wimlib;a=commitdiff_plain;h=56f882a80475fbe170f3d580400eb6f011ec5dfb LZX decompression: Cleanup No change in behavior. --- diff --git a/Makefile.am b/Makefile.am index 0d3d0f04..c6efa2ce 100644 --- a/Makefile.am +++ b/Makefile.am @@ -107,6 +107,7 @@ libwim_la_SOURCES = \ include/wimlib/lz_suffix_array_utils.h \ include/wimlib/lzms.h \ include/wimlib/lzx.h \ + include/wimlib/lzx_constants.h \ include/wimlib/metadata.h \ include/wimlib/pathlist.h \ include/wimlib/paths.h \ diff --git a/include/wimlib/decompress_common.h b/include/wimlib/decompress_common.h index 2b5d4f65..856c6411 100644 --- a/include/wimlib/decompress_common.h +++ b/include/wimlib/decompress_common.h @@ -230,7 +230,7 @@ make_huffman_decode_table(u16 decode_table[], unsigned num_syms, * This function won't write any data beyond this position. */ static inline void -lz_copy(u8 *dst, unsigned length, unsigned offset, const u8 *winend) +lz_copy(u8 *dst, u32 length, u32 offset, const u8 *winend) { const u8 *src = dst - offset; #if defined(__x86_64__) || defined(__i386__) diff --git a/include/wimlib/lzx.h b/include/wimlib/lzx.h index 539edf30..576d8bd5 100644 --- a/include/wimlib/lzx.h +++ b/include/wimlib/lzx.h @@ -1,12 +1,15 @@ +/* + * lzx.h + * + * Declarations shared between LZX compression and decompression. + */ + #ifndef _WIMLIB_LZX_H #define _WIMLIB_LZX_H -/* Constants for the LZX data compression format. See the comments in - * lzx-compress.c and lzx-decompress.c for more information about this format. - * */ - #include "wimlib/assert.h" #include "wimlib/compiler.h" +#include "wimlib/lzx_constants.h" #include "wimlib/util.h" #include "wimlib/types.h" @@ -19,77 +22,6 @@ # define LZX_ASSERT(...) #endif -/* Constants, most of which are defined by the LZX specification: */ - -/* The smallest and largest allowed match lengths. */ -#define LZX_MIN_MATCH_LEN 2 -#define LZX_MAX_MATCH_LEN 257 - -/* Number of values an uncompressed literal byte can represent. */ -#define LZX_NUM_CHARS 256 - -/* Each LZX block begins with 3 bits that determines the block type. Below are - * the valid block types. Values 0, and 4 through 7, are invalid. */ -#define LZX_BLOCKTYPE_VERBATIM 1 -#define LZX_BLOCKTYPE_ALIGNED 2 -#define LZX_BLOCKTYPE_UNCOMPRESSED 3 - -#define LZX_NUM_PRIMARY_LENS 7 - -/* The number of position slots varies from 30 to 51 depending on the window - * size (see comment in lzx-decompress.c). */ -#define LZX_MAX_POSITION_SLOTS 51 - -#define LZX_MIN_WINDOW_ORDER 15 -#define LZX_MAX_WINDOW_ORDER 21 -#define LZX_MIN_WINDOW_SIZE (1U << LZX_MIN_WINDOW_ORDER) /* 32768 */ -#define LZX_MAX_WINDOW_SIZE (1U << LZX_MAX_WINDOW_ORDER) /* 2097152 */ - -/* Read the LZX specification for information about the Huffman trees used in - * the LZX compression format. Basically there are 4 of them: The main tree, - * the length tree, the pre tree, and the aligned tree. The main tree and - * length tree are given at the beginning of VERBATIM and ALIGNED blocks as a - * list of *_NUM_SYMBOLS code length values. They are read using the - * read_code_lens() function and built using the make_decode_table() function. - * The decode table is not a real tree but rather a table that we can index by - * some number of bits (*_TABLEBITS) of the input to quickly look up the symbol - * corresponding to a Huffman code. - * - * The ALIGNED tree is only present on ALIGNED blocks. - * - * A PRECODE is used to encode the code lengths for the main tree and the length - * tree. There is a separate pretree for each half of the main tree. */ - -#define LZX_MAINCODE_MAX_NUM_SYMBOLS (LZX_NUM_CHARS + (LZX_MAX_POSITION_SLOTS << 3)) -#define LZX_MAINCODE_TABLEBITS 11 - -#define LZX_LENCODE_NUM_SYMBOLS 249 -#define LZX_LENCODE_TABLEBITS 10 - -#define LZX_PRECODE_NUM_SYMBOLS 20 -#define LZX_PRECODE_TABLEBITS 6 -#define LZX_PRECODE_ELEMENT_SIZE 4 - -#define LZX_ALIGNEDCODE_NUM_SYMBOLS 8 -#define LZX_ALIGNEDCODE_TABLEBITS 7 -#define LZX_ALIGNEDCODE_ELEMENT_SIZE 3 - -/* Maximum allowed length of Huffman codewords. */ -#define LZX_MAX_MAIN_CODEWORD_LEN 16 -#define LZX_MAX_LEN_CODEWORD_LEN 16 -#define LZX_MAX_PRE_CODEWORD_LEN 16 -#define LZX_MAX_ALIGNED_CODEWORD_LEN 8 - -/* For the LZX-compressed blocks in WIM files, this value is always used as the - * filesize parameter for the call instruction (0xe8 byte) preprocessing, even - * though the blocks themselves are not this size, and the size of the actual - * file resource in the WIM file is very likely to be something entirely - * different as well. */ -#define LZX_WIM_MAGIC_FILESIZE 12000000 - -/* Assumed LZX block size when the encoded block size begins with a 0 bit. */ -#define LZX_DEFAULT_BLOCK_SIZE 32768 - #define USE_LZX_EXTRA_BITS_ARRAY #ifdef USE_LZX_EXTRA_BITS_ARRAY @@ -138,8 +70,6 @@ lzx_get_position_slot_raw(u32 formatted_offset) extern bool lzx_window_size_valid(size_t window_size); extern unsigned lzx_get_num_main_syms(u32 window_size); -#define LZX_NUM_RECENT_OFFSETS 3 - /* Least-recently used queue for match offsets. */ struct lzx_lru_queue { u32 R[LZX_NUM_RECENT_OFFSETS]; @@ -147,14 +77,10 @@ struct lzx_lru_queue { #ifdef __x86_64__ _aligned_attribute(8) /* Improves performance of LZX compression by 1% - 2%; specifically, this speeds up - lzx_choose_near_optimal_match(). */ + lzx_choose_near_optimal_item(). */ #endif ; -/* In the LZX format, an offset of n bytes is actually encoded - * as (n + LZX_OFFSET_OFFSET). */ -#define LZX_OFFSET_OFFSET (LZX_NUM_RECENT_OFFSETS - 1) - /* Initialize the LZX least-recently-used match offset queue at the beginning of * a new window for either decompression or compression. */ static inline void @@ -165,9 +91,9 @@ lzx_lru_queue_init(struct lzx_lru_queue *queue) } extern void -lzx_do_e8_preprocessing(u8 *data, s32 size); +lzx_do_e8_preprocessing(u8 *data, u32 size); extern void -lzx_undo_e8_preprocessing(u8 *data, s32 size); +lzx_undo_e8_preprocessing(u8 *data, u32 size); #endif /* _WIMLIB_LZX_H */ diff --git a/include/wimlib/lzx_constants.h b/include/wimlib/lzx_constants.h new file mode 100644 index 00000000..36e812d8 --- /dev/null +++ b/include/wimlib/lzx_constants.h @@ -0,0 +1,78 @@ +/* + * lzx_constants.h + * + * Constants for the LZX compression format. + */ + +#ifndef _LZX_CONSTANTS_H +#define _LZX_CONSTANTS_H + +/* The smallest and largest allowed match lengths. */ +#define LZX_MIN_MATCH_LEN 2 +#define LZX_MAX_MATCH_LEN 257 + +/* Number of values an uncompressed literal byte can represent. */ +#define LZX_NUM_CHARS 256 + +/* Valid values of the 3-bit block type field. */ +#define LZX_BLOCKTYPE_VERBATIM 1 +#define LZX_BLOCKTYPE_ALIGNED 2 +#define LZX_BLOCKTYPE_UNCOMPRESSED 3 + +/* Maximum value of the "length header" portion of a main symbol. If the length + * header has this value, then the match length is at least LZX_NUM_PRIMARY_LENS + * + LZX_MIN_MATCH_LEN, and a length symbol follows. */ +#define LZX_NUM_PRIMARY_LENS 7 + +/* Maximum number of position slots. The actual number of position slots will + * depend on the window size. */ +#define LZX_MAX_POSITION_SLOTS 51 + +#define LZX_MIN_WINDOW_ORDER 15 +#define LZX_MAX_WINDOW_ORDER 21 +#define LZX_MIN_WINDOW_SIZE (1U << LZX_MIN_WINDOW_ORDER) /* 32768 */ +#define LZX_MAX_WINDOW_SIZE (1U << LZX_MAX_WINDOW_ORDER) /* 2097152 */ + +/* Maximum number of symbols in the main code. The actual number of symbols in + * the main code will depend on the window size. */ +#define LZX_MAINCODE_MAX_NUM_SYMBOLS (LZX_NUM_CHARS + (LZX_MAX_POSITION_SLOTS << 3)) + +/* Number of symbols in the length code. */ +#define LZX_LENCODE_NUM_SYMBOLS 249 + +/* Number of symbols in the pre-code. */ +#define LZX_PRECODE_NUM_SYMBOLS 20 + +/* Number of bits in which each pre-code codeword length is represented. */ +#define LZX_PRECODE_ELEMENT_SIZE 4 + +/* Number of symbols in the aligned offset code. */ +#define LZX_ALIGNEDCODE_NUM_SYMBOLS 8 + +/* Number of bits in which each aligned offset codeword length is represented. */ +#define LZX_ALIGNEDCODE_ELEMENT_SIZE 3 + +/* Maximum lengths (in bits) for length-limited Huffman code construction. */ +#define LZX_MAX_MAIN_CODEWORD_LEN 16 +#define LZX_MAX_LEN_CODEWORD_LEN 16 +#define LZX_MAX_PRE_CODEWORD_LEN 16 +#define LZX_MAX_ALIGNED_CODEWORD_LEN 8 + +/* For LZX-compressed blocks in WIM resources, this value is always used as the + * filesize parameter for the call instruction (0xe8 byte) preprocessing, even + * though the blocks themselves are not this size, and the size of the actual + * file resource in the WIM file is very likely to be something entirely + * different as well. */ +#define LZX_WIM_MAGIC_FILESIZE 12000000 + +/* Assumed LZX block size when the encoded block size begins with a 0 bit. + * This is probably WIM-specific. */ +#define LZX_DEFAULT_BLOCK_SIZE 32768 + +/* Number of offsets in the recent (or "repeat") offsets queue. */ +#define LZX_NUM_RECENT_OFFSETS 3 + +/* An offset of n bytes is actually encoded as (n + LZX_OFFSET_OFFSET). */ +#define LZX_OFFSET_OFFSET (LZX_NUM_RECENT_OFFSETS - 1) + +#endif /* _LZX_CONSTANTS_H */ diff --git a/src/lzx-common.c b/src/lzx-common.c index 24bf9974..e61629e7 100644 --- a/src/lzx-common.c +++ b/src/lzx-common.c @@ -33,14 +33,8 @@ # include #endif -/* LZX uses what it calls 'position slots' to represent match offsets. - * What this means is that a small 'position slot' number and a small - * offset from that slot are encoded instead of one large offset for - * every match. - * - lzx_position_base is an index to the position slot bases - * - lzx_extra_bits states how many bits of offset-from-base data is needed. +/* Mapping: position slot => first match offset that uses that position slot. */ - const u32 lzx_position_base[LZX_MAX_POSITION_SLOTS] = { 0 , 1 , 2 , 3 , 4 , /* 0 --- 4 */ 6 , 8 , 12 , 16 , 24 , /* 5 --- 9 */ @@ -55,6 +49,8 @@ const u32 lzx_position_base[LZX_MAX_POSITION_SLOTS] = { 2097152 /* 50 */ }; +/* Mapping: position slot => how many extra bits must be read and added to the + * corresponding position base to decode the match offset. */ #ifdef USE_LZX_EXTRA_BITS_ARRAY const u8 lzx_extra_bits[LZX_MAX_POSITION_SLOTS] = { 0 , 0 , 0 , 0 , 1 , @@ -193,7 +189,7 @@ inline /* Although inlining the 'process_target' function still speeds up the SSE2 case, it bloats the binary more. */ #endif void -lzx_e8_filter(u8 *data, s32 size, void (*process_target)(s32 *, s32)) +lzx_e8_filter(u8 *data, u32 size, void (*process_target)(s32 *, s32)) { #ifdef __SSE2__ /* SSE2 vectorized implementation for x86_64. This speeds up LZX @@ -288,13 +284,13 @@ lzx_e8_filter(u8 *data, s32 size, void (*process_target)(s32 *, s32)) } void -lzx_do_e8_preprocessing(u8 *data, s32 size) +lzx_do_e8_preprocessing(u8 *data, u32 size) { lzx_e8_filter(data, size, do_translate_target); } void -lzx_undo_e8_preprocessing(u8 *data, s32 size) +lzx_undo_e8_preprocessing(u8 *data, u32 size) { lzx_e8_filter(data, size, undo_translate_target); } diff --git a/src/lzx-decompress.c b/src/lzx-decompress.c index 16b46cb2..0c95ac03 100644 --- a/src/lzx-decompress.c +++ b/src/lzx-decompress.c @@ -1,9 +1,7 @@ /* * lzx-decompress.c * - * LZX decompression routines, originally based on code taken from cabextract - * v0.5, which was, itself, a modified version of the lzx decompression code - * from unlzx. + * A very fast decompressor for LZX, as used in WIM files. */ /* @@ -27,80 +25,31 @@ /* * LZX is an LZ77 and Huffman-code based compression format that has many - * similarities to the DEFLATE format used in zlib. The compression ratio is as - * good or better than DEFLATE. + * similarities to DEFLATE (the format used by zlib/gzip). The compression + * ratio is as good or better than DEFLATE. See lzx-compress.c for a format + * overview, and see https://en.wikipedia.org/wiki/LZX_(algorithm) for a + * historical overview. Here I make some pragmatic notes. * - * Some notes on the LZX compression format as used in Windows Imaging (WIM) - * files: + * The old specification for LZX is the document "Microsoft LZX Data Compression + * Format" (1997). It defines the LZX format as used in cabinet files. Allowed + * window sizes are 2^n where 15 <= n <= 21. However, this document contains + * several errors, so don't read too much into it... * - * A compressed WIM resource consists of a table of chunk offsets followed by - * the compressed chunks themselves. All compressed chunks except possibly the - * last decompress to a fixed number of bytes, by default 32768. This is quite - * similar to the cabinet (.cab) file format, but they are not the same. - * According to the cabinet format documentation, the LZX block size is - * independent from the CFDATA blocks, and an LZX block may span several CFDATA - * blocks. However, in WIMs, LZX blocks do not appear to ever span multiple WIM - * chunks. Note that this means any WIM chunk may be decompressed or compressed - * independently from any other chunk, which allows random access. + * The new specification for LZX is the document "[MS-PATCH]: LZX DELTA + * Compression and Decompression" (2014). It defines the LZX format as used by + * Microsoft's binary patcher. It corrects several errors in the 1997 document + * and extends the format in several ways --- namely, optional reference data, + * up to 2^25 byte windows, and longer match lengths. * - * An LZX compressed WIM chunk contains one or more LZX blocks of the aligned, - * verbatim, or uncompressed block types. For aligned and verbatim blocks, the - * size of the block in uncompressed bytes is specified by a bit following the 3 - * bits that specify the block type, possibly followed by an additional 16 bits. - * '1' means to use the default block size (equal to 32768, the default size of - * a WIM chunk), while '0' means that the block size is provided by the next 16 - * bits. + * WIM files use a more restricted form of LZX. No LZX DELTA extensions are + * present, the window is not "sliding", E8 preprocessing is done + * unconditionally with a fixed file size, and the maximum window size is always + * 2^15 bytes (equal to the size of each "chunk" in a compressed WIM resource). + * This code is primarily intended to implement this form of LZX. But although + * not compatible with WIMGAPI, this code also supports maximum window sizes up + * to 2^21 bytes. * - * The cabinet format, as documented, allows for the possibility that a - * compressed CFDATA chunk is up to 6144 bytes larger than the data it - * uncompresses to. However, in the WIM format it appears that every chunk that - * would be 32768 bytes or more when compressed is actually stored fully - * uncompressed. - * - * The 'e8' preprocessing step that changes x86 call instructions to use - * absolute offsets instead of relative offsets relies on a filesize parameter. - * There is no such parameter for this in the WIM files (even though the size of - * the file resource could be used for this purpose), and instead a magic file - * size of 12000000 is used. The 'e8' preprocessing is always done, and there - * is no bit to indicate whether it is done or not. - */ - -/* - * Some more notes about errors in Microsoft's LZX documentation: - * - * Microsoft's LZX document and their implementation of the com.ms.util.cab Java - * package do not concur. - * - * In the LZX document, there is a table showing the correlation between window - * size and the number of position slots. It states that the 1MB window = 40 - * slots and the 2MB window = 42 slots. In the implementation, 1MB = 42 slots, - * 2MB = 50 slots. The actual calculation is 'find the first slot whose position - * base is equal to or more than the required window size'. This would explain - * why other tables in the document refer to 50 slots rather than 42. - * - * The constant NUM_PRIMARY_LENS used in the decompression pseudocode is not - * defined in the specification. - * - * The LZX document states that aligned offset blocks have their aligned offset - * Huffman tree AFTER the main and length trees. The implementation suggests - * that the aligned offset tree is BEFORE the main and length trees. - * - * The LZX document decoding algorithm states that, in an aligned offset block, - * if an extra_bits value is 1, 2 or 3, then that number of bits should be read - * and the result added to the match offset. This is correct for 1 and 2, but - * not 3, where just a Huffman symbol (using the aligned tree) should be read. - * - * Regarding the E8 preprocessing, the LZX document states 'No translation may - * be performed on the last 6 bytes of the input block'. This is correct. - * However, the pseudocode provided checks for the *E8 leader* up to the last 6 - * bytes. If the leader appears between -10 and -7 bytes from the end, this - * would cause the next four bytes to be modified, at least one of which would - * be in the last 6 bytes, which is not allowed according to the spec. - * - * The specification states that the Huffman trees must always contain at least - * one element. However, many CAB files contain blocks where the length tree is - * completely empty (because there are no matches), and this is expected to - * succeed. + * TODO: Add support for window sizes up to 2^25 bytes. */ #ifdef HAVE_CONFIG_H @@ -115,165 +64,182 @@ #include -/* Huffman decoding tables and maps from symbols to code lengths. */ +/* These values are chosen for fast decompression. */ +#define LZX_MAINCODE_TABLEBITS 11 +#define LZX_LENCODE_TABLEBITS 10 +#define LZX_PRECODE_TABLEBITS 6 +#define LZX_ALIGNEDCODE_TABLEBITS 7 + +/* Huffman decoding tables, and arrays that map symbols to codeword lengths. */ struct lzx_tables { - u16 maintree_decode_table[(1 << LZX_MAINCODE_TABLEBITS) + + u16 maincode_decode_table[(1 << LZX_MAINCODE_TABLEBITS) + (LZX_MAINCODE_MAX_NUM_SYMBOLS * 2)] _aligned_attribute(DECODE_TABLE_ALIGNMENT); - u8 maintree_lens[LZX_MAINCODE_MAX_NUM_SYMBOLS]; + u8 maincode_lens[LZX_MAINCODE_MAX_NUM_SYMBOLS]; - u16 lentree_decode_table[(1 << LZX_LENCODE_TABLEBITS) + + u16 lencode_decode_table[(1 << LZX_LENCODE_TABLEBITS) + (LZX_LENCODE_NUM_SYMBOLS * 2)] _aligned_attribute(DECODE_TABLE_ALIGNMENT); - u8 lentree_lens[LZX_LENCODE_NUM_SYMBOLS]; + u8 lencode_lens[LZX_LENCODE_NUM_SYMBOLS]; - u16 alignedtree_decode_table[(1 << LZX_ALIGNEDCODE_TABLEBITS) + + u16 alignedcode_decode_table[(1 << LZX_ALIGNEDCODE_TABLEBITS) + (LZX_ALIGNEDCODE_NUM_SYMBOLS * 2)] _aligned_attribute(DECODE_TABLE_ALIGNMENT); - u8 alignedtree_lens[LZX_ALIGNEDCODE_NUM_SYMBOLS]; + u8 alignedcode_lens[LZX_ALIGNEDCODE_NUM_SYMBOLS]; } _aligned_attribute(DECODE_TABLE_ALIGNMENT); +/* The main LZX decompressor structure. + * + * Note: we keep track of most of the decompression state outside this + * structure. This structure only exists so that (1) we can store + * @max_window_size and @num_main_syms for multiple calls to lzx_decompress(); + * and (2) so that we don't have to allocate the large 'struct lzx_tables' on + * the stack. */ struct lzx_decompressor { u32 max_window_size; unsigned num_main_syms; struct lzx_tables tables; }; -/* - * Reads a Huffman-encoded symbol using the pre-tree. - */ +/* Read a Huffman-encoded symbol using the precode. */ static inline u16 -read_huffsym_using_pretree(struct input_bitstream *istream, - const u16 pretree_decode_table[]) +read_huffsym_using_precode(struct input_bitstream *istream, + const u16 precode_decode_table[]) { - return read_huffsym(istream, pretree_decode_table, + return read_huffsym(istream, precode_decode_table, LZX_PRECODE_TABLEBITS, LZX_MAX_PRE_CODEWORD_LEN); } -/* Reads a Huffman-encoded symbol using the main tree. */ +/* Read a Huffman-encoded symbol using the main code. */ static inline u16 -read_huffsym_using_maintree(struct input_bitstream *istream, +read_huffsym_using_maincode(struct input_bitstream *istream, const struct lzx_tables *tables) { - return read_huffsym(istream, tables->maintree_decode_table, + return read_huffsym(istream, tables->maincode_decode_table, LZX_MAINCODE_TABLEBITS, LZX_MAX_MAIN_CODEWORD_LEN); } -/* Reads a Huffman-encoded symbol using the length tree. */ +/* Read a Huffman-encoded symbol using the length code. */ static inline u16 -read_huffsym_using_lentree(struct input_bitstream *istream, +read_huffsym_using_lencode(struct input_bitstream *istream, const struct lzx_tables *tables) { - return read_huffsym(istream, tables->lentree_decode_table, + return read_huffsym(istream, tables->lencode_decode_table, LZX_LENCODE_TABLEBITS, LZX_MAX_LEN_CODEWORD_LEN); } -/* Reads a Huffman-encoded symbol using the aligned offset tree. */ +/* Read a Huffman-encoded symbol using the aligned offset code. */ static inline u16 -read_huffsym_using_alignedtree(struct input_bitstream *istream, +read_huffsym_using_alignedcode(struct input_bitstream *istream, const struct lzx_tables *tables) { - return read_huffsym(istream, tables->alignedtree_decode_table, + return read_huffsym(istream, tables->alignedcode_decode_table, LZX_ALIGNEDCODE_TABLEBITS, LZX_MAX_ALIGNED_CODEWORD_LEN); } /* - * Reads the pretree from the input, then uses the pretree to decode @num_lens - * code length values from the input. + * Read the precode from the compressed input bitstream, then use it to decode + * @num_lens codeword length values. * - * @istream: The bit stream for the input. It is positioned on the beginning - * of the pretree for the code length values. - * @lens: An array that contains the length values from the previous time - * the code lengths for this Huffman tree were read, or all - * 0's if this is the first time. - * @num_lens: Number of length values to decode and return. + * @istream: + * The input bitstream. * + * @lens: + * An array that contains the length values from the previous time the + * codeword lengths for this Huffman code were read, or all 0's if this is + * the first time. + * + * @num_lens: + * Number of length values to decode. + * + * Returns 0 on success, or -1 if the data was invalid. */ static int -lzx_read_code_lens(struct input_bitstream *istream, u8 lens[], - unsigned num_lens) +lzx_read_codeword_lens(struct input_bitstream *istream, u8 lens[], unsigned num_lens) { - /* Declare the decoding table and length table for the pretree. */ - u16 pretree_decode_table[(1 << LZX_PRECODE_TABLEBITS) + + /* Declare the decoding table and length table for the precode. */ + u16 precode_decode_table[(1 << LZX_PRECODE_TABLEBITS) + (LZX_PRECODE_NUM_SYMBOLS * 2)] _aligned_attribute(DECODE_TABLE_ALIGNMENT); - u8 pretree_lens[LZX_PRECODE_NUM_SYMBOLS]; - unsigned i; + u8 precode_lens[LZX_PRECODE_NUM_SYMBOLS]; int ret; - /* Read the code lengths of the pretree codes. There are 20 lengths of - * 4 bits each. */ - for (i = 0; i < LZX_PRECODE_NUM_SYMBOLS; i++) { - pretree_lens[i] = bitstream_read_bits(istream, + /* Read the lengths of the precode codewords. These are given + * explicitly. */ + for (int i = 0; i < LZX_PRECODE_NUM_SYMBOLS; i++) { + precode_lens[i] = bitstream_read_bits(istream, LZX_PRECODE_ELEMENT_SIZE); } - /* Make the decoding table for the pretree. */ - ret = make_huffman_decode_table(pretree_decode_table, + /* Make the decoding table for the precode. */ + ret = make_huffman_decode_table(precode_decode_table, LZX_PRECODE_NUM_SYMBOLS, LZX_PRECODE_TABLEBITS, - pretree_lens, + precode_lens, LZX_MAX_PRE_CODEWORD_LEN); if (ret) return ret; - /* Pointer past the last length value that needs to be filled in. */ + /* Pointer past the last length value that needs to be filled in. */ u8 *lens_end = lens + num_lens; - while (1) { - - /* Decode a symbol from the input. If the symbol is between 0 - * and 16, it is the difference from the old length. If it is - * between 17 and 19, it is a special code that indicates that - * some number of the next lengths are all 0, or some number of - * the next lengths are all equal to the next symbol in the - * input. */ - unsigned tree_code; - u32 num_zeroes; - unsigned code; - u32 num_same; + for (;;) { + + unsigned presym; + unsigned run_len; signed char value; - tree_code = read_huffsym_using_pretree(istream, - pretree_decode_table); - switch (tree_code) { - case 17: /* Run of 0's */ - num_zeroes = bitstream_read_bits(istream, 4); - num_zeroes += 4; - while (num_zeroes--) { + /* Decode a symbol from the input. + * + * If the symbol is between 0 and 16, it is the difference from + * the old length, modulo 17. + * + * If the symbol is between 17 and 19, it is a special symbol + * that indicates that some number of the next lengths are all + * 0, or that some number of the next lengths are all equal to + * the next symbol. */ + + presym = read_huffsym_using_precode(istream, + precode_decode_table); + switch (presym) { + + case 17: /* Run of 0's */ + run_len = 4 + bitstream_read_bits(istream, 4); + do { *lens = 0; if (++lens == lens_end) return 0; - } + } while (--run_len); break; - case 18: /* Longer run of 0's */ - num_zeroes = bitstream_read_bits(istream, 5); - num_zeroes += 20; - while (num_zeroes--) { + + case 18: /* Longer run of 0's */ + run_len = 20 + bitstream_read_bits(istream, 5); + do { *lens = 0; if (++lens == lens_end) return 0; - } + } while (--run_len); break; - case 19: /* Run of identical lengths */ - num_same = bitstream_read_bits(istream, 1); - num_same += 4; - code = read_huffsym_using_pretree(istream, - pretree_decode_table); - value = (signed char)*lens - (signed char)code; + + case 19: /* Run of identical lengths */ + run_len = 4 + bitstream_read_bits(istream, 1); + presym = read_huffsym_using_precode(istream, + precode_decode_table); + value = (signed char)*lens - (signed char)presym; if (value < 0) value += 17; - while (num_same--) { + do { *lens = value; if (++lens == lens_end) return 0; - } + } while (--run_len); break; - default: /* Difference from old length. */ - value = (signed char)*lens - (signed char)tree_code; + + default: /* Difference from old length */ + value = (signed char)*lens - (signed char)presym; if (value < 0) value += 17; *lens = value; @@ -285,40 +251,37 @@ lzx_read_code_lens(struct input_bitstream *istream, u8 lens[], } /* - * Reads the header for an LZX-compressed block. + * Read the header of an LZX block and save the block type and size in + * *block_type_ret and *block_size_ret, respectively. * - * @istream: The input bitstream. - * @block_size_ret: A pointer to an int into which the size of the block, - * in bytes, will be returned. - * @block_type_ret: A pointer to an int into which the type of the block - * (LZX_BLOCKTYPE_*) will be returned. - * @tables: A pointer to an lzx_tables structure in which the - * main tree, the length tree, and possibly the - * aligned offset tree will be constructed. - * @queue: A pointer to the least-recently-used queue into which - * R0, R1, and R2 will be written (only for uncompressed - * blocks, which contain this information in the header) + * If the block is compressed, also update the Huffman decode @tables with the + * new Huffman codes. + * + * If the block is uncompressed, also update the match offset @queue with the + * new match offsets. + * + * Return 0 on success, or -1 if the data was invalid. */ static int lzx_read_block_header(struct input_bitstream *istream, unsigned num_main_syms, - unsigned max_window_size, - unsigned *block_size_ret, - unsigned *block_type_ret, + u32 max_window_size, + int *block_type_ret, + u32 *block_size_ret, struct lzx_tables *tables, struct lzx_lru_queue *queue) { + int block_type; + u32 block_size; int ret; - unsigned block_type; - unsigned block_size; bitstream_ensure_bits(istream, 4); - /* The first three bits tell us what kind of block it is, and are one - * of the LZX_BLOCKTYPE_* values. */ + /* The first three bits tell us what kind of block it is, and should be + * one of the LZX_BLOCKTYPE_* values. */ block_type = bitstream_pop_bits(istream, 3); - /* Read the block size. This mirrors the behavior + /* Read the block size. This mirrors the behavior of * lzx_write_compressed_block() in lzx-compress.c; see that for more * details. */ if (bitstream_pop_bits(istream, 1)) { @@ -341,118 +304,89 @@ lzx_read_block_header(struct input_bitstream *istream, } switch (block_type) { + case LZX_BLOCKTYPE_ALIGNED: - /* Read the path lengths for the elements of the aligned tree, - * then build it. */ - for (unsigned i = 0; i < LZX_ALIGNEDCODE_NUM_SYMBOLS; i++) { - tables->alignedtree_lens[i] = + /* Read the aligned offset code and prepare its decode table. + */ + + for (int i = 0; i < LZX_ALIGNEDCODE_NUM_SYMBOLS; i++) { + tables->alignedcode_lens[i] = bitstream_read_bits(istream, LZX_ALIGNEDCODE_ELEMENT_SIZE); } - LZX_DEBUG("Building the aligned tree."); - ret = make_huffman_decode_table(tables->alignedtree_decode_table, + ret = make_huffman_decode_table(tables->alignedcode_decode_table, LZX_ALIGNEDCODE_NUM_SYMBOLS, LZX_ALIGNEDCODE_TABLEBITS, - tables->alignedtree_lens, + tables->alignedcode_lens, LZX_MAX_ALIGNED_CODEWORD_LEN); - if (ret) { - LZX_DEBUG("Failed to make the decode table for the " - "aligned offset tree"); + if (ret) return ret; - } /* Fall though, since the rest of the header for aligned offset - * blocks is the same as that for verbatim blocks */ + * blocks is the same as that for verbatim blocks. */ case LZX_BLOCKTYPE_VERBATIM: - if (block_type == LZX_BLOCKTYPE_VERBATIM) - LZX_DEBUG("Found verbatim block."); - - LZX_DEBUG("Reading path lengths for main tree."); - /* Read the path lengths for the first 256 elements of the main - * tree. */ - ret = lzx_read_code_lens(istream, tables->maintree_lens, - LZX_NUM_CHARS); - if (ret) { - LZX_DEBUG("Failed to read the code lengths for the " - "first 256 elements of the main tree"); - return ret; - } - /* Read the path lengths for the remaining elements of the main - * tree. */ - LZX_DEBUG("Reading path lengths for remaining elements of " - "main tree (%d elements).", - num_main_syms - LZX_NUM_CHARS); - ret = lzx_read_code_lens(istream, - tables->maintree_lens + LZX_NUM_CHARS, - num_main_syms - LZX_NUM_CHARS); - if (ret) { - LZX_DEBUG("Failed to read the path lengths for the " - "remaining elements of the main tree"); + /* Read the main code and prepare its decode table. + * + * Note that the codeword lengths in the main code are encoded + * in two parts: one part for literal symbols, and one part for + * match symbols. */ + + ret = lzx_read_codeword_lens(istream, tables->maincode_lens, + LZX_NUM_CHARS); + if (ret) return ret; - } - LZX_DEBUG("Building the Huffman decoding " - "table for the main tree."); + ret = lzx_read_codeword_lens(istream, + tables->maincode_lens + LZX_NUM_CHARS, + num_main_syms - LZX_NUM_CHARS); + if (ret) + return ret; - ret = make_huffman_decode_table(tables->maintree_decode_table, + ret = make_huffman_decode_table(tables->maincode_decode_table, num_main_syms, LZX_MAINCODE_TABLEBITS, - tables->maintree_lens, + tables->maincode_lens, LZX_MAX_MAIN_CODEWORD_LEN); - if (ret) { - LZX_DEBUG("Failed to make the decode " - "table for the main tree"); + if (ret) return ret; - } - LZX_DEBUG("Reading path lengths for the length tree."); - ret = lzx_read_code_lens(istream, tables->lentree_lens, - LZX_LENCODE_NUM_SYMBOLS); - if (ret) { - LZX_DEBUG("Failed to read the path " - "lengths for the length tree"); + /* Read the length code and prepare its decode table. */ + + ret = lzx_read_codeword_lens(istream, tables->lencode_lens, + LZX_LENCODE_NUM_SYMBOLS); + if (ret) return ret; - } - LZX_DEBUG("Building the length tree."); - ret = make_huffman_decode_table(tables->lentree_decode_table, + ret = make_huffman_decode_table(tables->lencode_decode_table, LZX_LENCODE_NUM_SYMBOLS, LZX_LENCODE_TABLEBITS, - tables->lentree_lens, + tables->lencode_lens, LZX_MAX_LEN_CODEWORD_LEN); - if (ret) { - LZX_DEBUG("Failed to build the length Huffman tree"); + if (ret) return ret; - } - /* The bitstream of compressed literals and matches for this - * block directly follows and will be read in - * lzx_decompress_block(). */ + break; + case LZX_BLOCKTYPE_UNCOMPRESSED: - LZX_DEBUG("Found uncompressed block."); + /* Before reading the three LRU match offsets from the - * uncompressed block header, the stream needs to be aligned on - * a 16-bit boundary. But, unexpectedly, if the stream is + * uncompressed block header, the stream must be aligned on a + * 16-bit boundary. But, unexpectedly, if the stream is * *already* aligned, the correct thing to do is to throw away - * the next 16 bits. */ + * the next 16 bits. */ + if (istream->bitsleft == 0) { - if (istream->data_bytes_left < 14) { - LZX_DEBUG("Insufficient length in " - "uncompressed block"); + if (istream->data_bytes_left < 14) return -1; - } istream->data += 2; istream->data_bytes_left -= 2; } else { - if (istream->data_bytes_left < 12) { - LZX_DEBUG("Insufficient length in " - "uncompressed block"); + if (istream->data_bytes_left < 12) return -1; - } istream->bitsleft = 0; istream->bitbuf = 0; } @@ -461,86 +395,56 @@ lzx_read_block_header(struct input_bitstream *istream, queue->R[2] = le32_to_cpu(*(le32*)(istream->data + 8)); istream->data += 12; istream->data_bytes_left -= 12; - /* The uncompressed data of this block directly follows and will - * be read in lzx_decompress(). */ break; + default: - LZX_DEBUG("Found invalid block"); + /* Unrecognized block type. */ return -1; } + *block_type_ret = block_type; *block_size_ret = block_size; return 0; } /* - * Decodes a compressed match from a block of LZX-compressed data. A match - * refers to some match_offset to a point earlier in the window as well as some - * match_len, for which the data is to be copied to the current position in the - * window. - * - * @main_element: The start of the match data, as decoded using the main - * tree. - * - * @block_type: The type of the block (LZX_BLOCKTYPE_ALIGNED or - * LZX_BLOCKTYPE_VERBATIM) - * - * @bytes_remaining: The amount of uncompressed data remaining to be - * uncompressed in this block. It is an error if the match - * is longer than this number. - * - * @window: A pointer to the window into which the uncompressed - * data is being written. - * - * @window_pos: The current byte offset in the window. - * - * @tables: The Huffman decoding tables for this LZX block (main - * code, length code, and for LZX_BLOCKTYPE_ALIGNED blocks, - * also the aligned offset code). - * - * @queue: The least-recently used queue for match offsets. + * Decode a match and copy its bytes into the decompression window. * - * @istream: The input bitstream. - * - * Returns the length of the match, or a negative number on error. The possible - * error cases are: - * - Match would exceed the amount of data remaining to be uncompressed. - * - Match refers to data before the window. - * - The input bitstream ended unexpectedly. + * Return the length of the match in bytes, or 0 if the match underflowed the + * window or overflowed the current block. */ -static int -lzx_decode_match(unsigned main_element, int block_type, - unsigned bytes_remaining, u8 *window, - unsigned window_pos, +static u32 +lzx_decode_match(unsigned main_symbol, int block_type, + u32 bytes_remaining, u8 *window, u32 window_pos, const struct lzx_tables *tables, struct lzx_lru_queue *queue, struct input_bitstream *istream) { unsigned length_header; unsigned position_slot; - unsigned match_len; - unsigned match_offset; + u32 match_len; + u32 match_offset; unsigned num_extra_bits; u32 verbatim_bits; u32 aligned_bits; - /* The main element is offset by 256 because values under 256 indicate a - * literal value. */ - main_element -= LZX_NUM_CHARS; + /* The main symbol is offset by 256 because values under 256 indicate a + * literal value. */ + main_symbol -= LZX_NUM_CHARS; /* The length header consists of the lower 3 bits of the main element. * The position slot is the rest of it. */ - length_header = main_element & LZX_NUM_PRIMARY_LENS; - position_slot = main_element >> 3; + length_header = main_symbol & LZX_NUM_PRIMARY_LENS; + position_slot = main_symbol >> 3; /* If the length_header is less than LZX_NUM_PRIMARY_LENS (= 7), it * gives the match length as the offset from LZX_MIN_MATCH_LEN. * Otherwise, the length is given by an additional symbol encoded using - * the length tree, offset by 9 (LZX_MIN_MATCH_LEN + + * the length code, offset by 9 (LZX_MIN_MATCH_LEN + * LZX_NUM_PRIMARY_LENS) */ match_len = LZX_MIN_MATCH_LEN + length_header; if (length_header == LZX_NUM_PRIMARY_LENS) - match_len += read_huffsym_using_lentree(istream, tables); + match_len += read_huffsym_using_lencode(istream, tables); /* If the position_slot is 0, 1, or 2, the match offset is retrieved * from the LRU queue. Otherwise, the match offset is not in the LRU @@ -565,8 +469,8 @@ lzx_decode_match(unsigned main_element, int block_type, /* For aligned blocks, if there are at least 3 extra bits, the * actual number of extra bits is 3 less, and they encode a * number of 8-byte words that are added to the offset; there - * is then an additional symbol read using the aligned tree that - * specifies the actual byte alignment. */ + * is then an additional symbol read using the aligned offset + * code that specifies the actual byte alignment. */ if (block_type == LZX_BLOCKTYPE_ALIGNED && num_extra_bits >= 3) { /* There is an error in the LZX "specification" at this @@ -579,7 +483,7 @@ lzx_decode_match(unsigned main_element, int block_type, verbatim_bits = bitstream_read_bits(istream, num_extra_bits - 3); verbatim_bits <<= 3; - aligned_bits = read_huffsym_using_alignedtree(istream, + aligned_bits = read_huffsym_using_alignedcode(istream, tables); } else { /* For non-aligned blocks, or for aligned blocks with @@ -600,23 +504,13 @@ lzx_decode_match(unsigned main_element, int block_type, queue->R[0] = match_offset; } - /* Verify that the match is in the bounds of the part of the window - * currently in use, then copy the source of the match to the current - * position. */ + /* Validate the match, then copy it to the current position. */ - if (unlikely(match_len > bytes_remaining)) { - LZX_DEBUG("Match of length %u bytes overflows " - "uncompressed block size", match_len); - return -1; - } + if (unlikely(match_len > bytes_remaining)) + return 0; - if (unlikely(match_offset > window_pos)) { - LZX_DEBUG("Match of length %u bytes references " - "data before window (match_offset = %u, " - "window_pos = %u)", - match_len, match_offset, window_pos); - return -1; - } + if (unlikely(match_offset > window_pos)) + return 0; lz_copy(&window[window_pos], match_len, match_offset, &window[window_pos + bytes_remaining]); @@ -625,50 +519,60 @@ lzx_decode_match(unsigned main_element, int block_type, } /* - * Decompresses an LZX-compressed block of data from which the header has already - * been read. + * Decompress an LZX-compressed block of data. + * + * @block_type: + * The type of the block (LZX_BLOCKTYPE_VERBATIM or LZX_BLOCKTYPE_ALIGNED). + * + * @block_size: + * The size of the block, in bytes. + * + * @window: + * Pointer to the beginning of the decompression window. + * + * @window_pos: + * The position in the window at which the block starts. + * + * @tables: + * The Huffman decoding tables for the block. * - * @block_type: The type of the block (LZX_BLOCKTYPE_VERBATIM or - * LZX_BLOCKTYPE_ALIGNED) - * @block_size: The size of the block, in bytes. - * @window: Pointer to the decompression window. - * @window_pos: The current position in the window. Will be 0 for the first - * block. - * @tables: The Huffman decoding tables for the block (main, length, and - * aligned offset, the latter only for LZX_BLOCKTYPE_ALIGNED) - * @queue: The least-recently-used queue for match offsets. - * @istream: The input bitstream for the compressed literals. + * @queue: + * The least-recently-used queue for match offsets. + * + * @istream: + * The input bitstream, positioned at the start of the block data. + * + * Returns 0 on success, or -1 if the data was invalid. */ static int -lzx_decompress_block(int block_type, unsigned block_size, - u8 *window, - unsigned window_pos, +lzx_decompress_block(int block_type, u32 block_size, + u8 *window, u32 window_pos, const struct lzx_tables *tables, struct lzx_lru_queue *queue, struct input_bitstream *istream) { - unsigned main_element; - unsigned end; - int match_len; - - end = window_pos + block_size; - while (window_pos < end) { - main_element = read_huffsym_using_maintree(istream, tables); - if (main_element < LZX_NUM_CHARS) { - /* literal: 0 to LZX_NUM_CHARS - 1 */ - window[window_pos++] = main_element; + u32 block_end; + unsigned main_symbol; + u32 match_len; + + block_end = window_pos + block_size; + while (window_pos < block_end) { + main_symbol = read_huffsym_using_maincode(istream, tables); + if (main_symbol < LZX_NUM_CHARS) { + /* Literal */ + window[window_pos++] = main_symbol; } else { - /* match: LZX_NUM_CHARS to num_main_syms - 1 */ - match_len = lzx_decode_match(main_element, + /* Match */ + match_len = lzx_decode_match(main_symbol, block_type, - end - window_pos, + block_end - window_pos, window, window_pos, tables, queue, istream); - if (unlikely(match_len < 0)) - return match_len; + if (unlikely(match_len == 0)) + return -1; window_pos += match_len; } } @@ -678,38 +582,32 @@ lzx_decompress_block(int block_type, unsigned block_size, static int lzx_decompress(const void *compressed_data, size_t compressed_size, void *uncompressed_data, size_t uncompressed_size, - void *_ctx) + void *_dec) { - struct lzx_decompressor *ctx = _ctx; + struct lzx_decompressor *dec = _dec; struct input_bitstream istream; struct lzx_lru_queue queue; - unsigned window_pos; - unsigned block_size; - unsigned block_type; + u32 window_pos; + int block_type; + u32 block_size; + bool may_have_e8_byte; int ret; - bool e8_preprocessing_done; - - LZX_DEBUG("compressed_data = %p, compressed_size = %zu, " - "uncompressed_data = %p, uncompressed_size = %zu, " - "max_window_size=%u).", - compressed_data, compressed_size, - uncompressed_data, uncompressed_size, - ctx->max_window_size); - - if (uncompressed_size > ctx->max_window_size) { - LZX_DEBUG("Uncompressed size of %zu exceeds " - "window size of %u!", - uncompressed_size, ctx->max_window_size); + + if (uncompressed_size > dec->max_window_size) return -1; - } - memset(ctx->tables.maintree_lens, 0, sizeof(ctx->tables.maintree_lens)); - memset(ctx->tables.lentree_lens, 0, sizeof(ctx->tables.lentree_lens)); - lzx_lru_queue_init(&queue); init_input_bitstream(&istream, compressed_data, compressed_size); - e8_preprocessing_done = false; /* Set to true if there may be 0xe8 bytes - in the uncompressed data. */ + /* Initialize the recent offsets queue. */ + lzx_lru_queue_init(&queue); + + /* Codeword lengths begin as all 0's for delta encoding purposes. */ + memset(dec->tables.maincode_lens, 0, sizeof(dec->tables.maincode_lens)); + memset(dec->tables.lencode_lens, 0, sizeof(dec->tables.lencode_lens)); + + /* Set this to true if there may be 0xe8 bytes in the uncompressed data. + */ + may_have_e8_byte = false; /* The compressed data will consist of one or more blocks. The * following loop decompresses one block, and it runs until there all @@ -720,96 +618,89 @@ lzx_decompress(const void *compressed_data, size_t compressed_size, window_pos < uncompressed_size; window_pos += block_size) { - LZX_DEBUG("Reading block header."); - ret = lzx_read_block_header(&istream, ctx->num_main_syms, - ctx->max_window_size, &block_size, - &block_type, &ctx->tables, &queue); + ret = lzx_read_block_header(&istream, dec->num_main_syms, + dec->max_window_size, &block_type, + &block_size, &dec->tables, &queue); if (ret) return ret; - LZX_DEBUG("block_size = %u, window_pos = %u", - block_size, window_pos); - - if (block_size > uncompressed_size - window_pos) { - LZX_DEBUG("Expected a block size of at " - "most %zu bytes (found %u bytes)", - uncompressed_size - window_pos, block_size); + if (block_size > uncompressed_size - window_pos) return -1; - } - switch (block_type) { - case LZX_BLOCKTYPE_VERBATIM: - case LZX_BLOCKTYPE_ALIGNED: - if (block_type == LZX_BLOCKTYPE_VERBATIM) - LZX_DEBUG("LZX_BLOCKTYPE_VERBATIM"); - else - LZX_DEBUG("LZX_BLOCKTYPE_ALIGNED"); + if (block_type != LZX_BLOCKTYPE_UNCOMPRESSED) { + + /* Compressed block. */ + ret = lzx_decompress_block(block_type, block_size, uncompressed_data, window_pos, - &ctx->tables, + &dec->tables, &queue, &istream); if (ret) return ret; - if (ctx->tables.maintree_lens[0xe8] != 0) - e8_preprocessing_done = true; - break; - case LZX_BLOCKTYPE_UNCOMPRESSED: - LZX_DEBUG("LZX_BLOCKTYPE_UNCOMPRESSED"); - if (istream.data_bytes_left < block_size) { - LZX_DEBUG("Unexpected end of input when " - "reading %u bytes from LZX bitstream " - "(only have %u bytes left)", - block_size, istream.data_bytes_left); + /* If the first 0xe8 byte was in this block, it must + * have been encoded as a literal using mainsym 0xe8. */ + if (dec->tables.maincode_lens[0xe8] != 0) + may_have_e8_byte = true; + } else { + + /* Uncompressed block. */ + + if (istream.data_bytes_left < block_size) return -1; - } + memcpy(&((u8*)uncompressed_data)[window_pos], istream.data, block_size); istream.data += block_size; istream.data_bytes_left -= block_size; - /* Re-align bitstream if an odd number of bytes were + + /* Re-align the bitstream if an odd number of bytes was * read. */ if (istream.data_bytes_left && (block_size & 1)) { istream.data_bytes_left--; istream.data++; } - e8_preprocessing_done = true; - break; + may_have_e8_byte = true; } } - if (e8_preprocessing_done) + + /* Postprocess the data unless it cannot possibly contain 0xe8 bytes */ + if (may_have_e8_byte) lzx_undo_e8_preprocessing(uncompressed_data, uncompressed_size); + return 0; } static void -lzx_free_decompressor(void *_ctx) +lzx_free_decompressor(void *_dec) { - struct lzx_decompressor *ctx = _ctx; + struct lzx_decompressor *dec = _dec; - ALIGNED_FREE(ctx); + ALIGNED_FREE(dec); } static int -lzx_create_decompressor(size_t max_window_size, void **ctx_ret) +lzx_create_decompressor(size_t max_window_size, void **dec_ret) { - struct lzx_decompressor *ctx; + struct lzx_decompressor *dec; if (!lzx_window_size_valid(max_window_size)) return WIMLIB_ERR_INVALID_PARAM; - ctx = ALIGNED_MALLOC(sizeof(struct lzx_decompressor), + /* The aligned allocation is needed to ensure that the lzx_tables are + * aligned properly. */ + dec = ALIGNED_MALLOC(sizeof(struct lzx_decompressor), DECODE_TABLE_ALIGNMENT); - if (ctx == NULL) + if (!dec) return WIMLIB_ERR_NOMEM; - ctx->max_window_size = max_window_size; - ctx->num_main_syms = lzx_get_num_main_syms(max_window_size); + dec->max_window_size = max_window_size; + dec->num_main_syms = lzx_get_num_main_syms(max_window_size); - *ctx_ret = ctx; + *dec_ret = dec; return 0; }