* decompress_common.h
*
* Header for decompression code shared by multiple compression formats.
+ *
+ * The author dedicates this file to the public domain.
+ * You can do whatever you want with this file.
*/
#ifndef _WIMLIB_DECOMPRESS_COMMON_H
#include "wimlib/assert.h"
#include "wimlib/compiler.h"
-#include "wimlib/error.h"
#include "wimlib/endianness.h"
#include "wimlib/types.h"
-#ifndef INPUT_IDX_T_DEFINED
-#define INPUT_IDX_T_DEFINED
-typedef u32 input_idx_t;
-#endif
-
/* Structure to encapsulate a block of in-memory data that is being interpreted
* as a stream of bits.
*
const u8 *data;
/* Number of bytes of data that are left. */
- input_idx_t data_bytes_left;
+ u32 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, input_idx_t num_data_bytes)
+ const void *data, u32 num_data_bytes)
{
istream->bitbuf = 0;
istream->bitsleft = 0;
return *istream->data++;
}
+
+/* Needed alignment of decode_table parameter to make_huffman_decode_table().
+ *
+ * Reason: We may fill the entries with SSE instructions without worrying
+ * about dealing with the unaligned case. */
+#define DECODE_TABLE_ALIGNMENT 16
+
+/* Maximum supported symbol count for make_huffman_decode_table().
+ *
+ * Reason: In direct mapping entries, we store the symbol in 11 bits. */
+#define DECODE_TABLE_MAX_SYMBOLS 2048
+
+/* Maximum supported table bits for make_huffman_decode_table().
+ *
+ * Reason: In internal binary tree nodes, offsets are encoded in 14 bits.
+ * But the real limit is 13, because we allocate entries past the end of
+ * the direct lookup part of the table for binary tree nodes. (Note: if
+ * needed this limit could be removed by encoding the offsets relative to
+ * &decode_table[1 << table_bits].) */
+#define DECODE_TABLE_MAX_TABLE_BITS 13
+
+/* Maximum supported codeword length for make_huffman_decode_table().
+ *
+ * Reason: In direct mapping entries, we encode the codeword length in 5
+ * bits, and the top 2 bits can't both be set because that has special
+ * meaning. */
+#define DECODE_TABLE_MAX_CODEWORD_LEN 23
+
/* Reads and returns the next Huffman-encoded symbol from a bitstream. If the
* input data is exhausted, the Huffman symbol is decoded as if the missing bits
- * are all zeroes. */
+ * are all zeroes.
+ *
+ * XXX: This is mostly duplicated in lzms_huffman_decode_symbol() in
+ * lzms-decompress.c. */
static inline u16
-read_huffsym(struct input_bitstream * restrict istream,
- const u16 decode_table[restrict],
- const u8 lens[restrict],
- unsigned num_syms,
- unsigned table_bits,
- unsigned max_codeword_len)
+read_huffsym(struct input_bitstream *istream, const u16 decode_table[],
+ unsigned table_bits, unsigned max_codeword_len)
{
+ u16 entry;
+ u16 key_bits;
bitstream_ensure_bits(istream, max_codeword_len);
- /* 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 (likely(sym < num_syms)) {
- /* Fast case: The decode table directly provided the symbol. */
- bitstream_remove_bits(istream, lens[sym]);
+ /* Index the decode table by the next table_bits bits of the input. */
+ key_bits = bitstream_peek_bits(istream, table_bits);
+ entry = decode_table[key_bits];
+ if (likely(entry < 0xC000)) {
+ /* Fast case: The decode table directly provided the
+ * symbol and codeword length. The low 11 bits are the
+ * symbol, and the high 5 bits are the codeword length. */
+ bitstream_remove_bits(istream, entry >> 11);
+ return entry & 0x7FF;
} else {
- /* Slow case: The symbol took too many bits to include directly
- * in the decode table, so search for it in a binary tree at the
- * end of the decode table. */
+ /* Slow case: The codeword for the symbol is longer than
+ * table_bits, so the symbol does not have an entry
+ * directly in the first (1 << table_bits) entries of the
+ * decode table. Traverse the appropriate binary tree
+ * bit-by-bit to decode the symbol. */
bitstream_remove_bits(istream, table_bits);
do {
- key_bits = sym + bitstream_pop_bits(istream, 1);
- } while ((sym = decode_table[key_bits]) >= num_syms);
+ key_bits = (entry & 0x3FFF) + bitstream_pop_bits(istream, 1);
+ } while ((entry = decode_table[key_bits]) >= 0xC000);
+ return entry;
}
- return sym;
}
extern int
make_huffman_decode_table(u16 decode_table[], unsigned num_syms,
- unsigned num_bits, const u8 lengths[],
+ unsigned num_bits, const u8 lens[],
unsigned max_codeword_len);
-/* Minimum alignment for the decode_table parameter to
- * make_huffman_decode_table(). */
-#define DECODE_TABLE_ALIGNMENT 16
-#endif /* _WIMLIB_DECOMPRESS_H */
+/*
+ * Copy a LZ77 match at (dst - offset) to dst.
+ *
+ * The length and offset must be already validated --- that is, (dst - offset)
+ * can't underrun the output buffer, and (dst + length) can't overrun the output
+ * buffer. Also, the length cannot be 0.
+ *
+ * @winend points to the byte past the end of the output buffer.
+ * This function won't write any data beyond this position.
+ */
+static inline void
+lz_copy(u8 *dst, unsigned length, unsigned offset, const u8 *winend)
+{
+ const u8 *src = dst - offset;
+#if defined(__x86_64__) || defined(__i386__)
+ /* Copy one 'unsigned long' at a time. On i386 and x86_64 this is
+ * faster than copying one byte at a time, unless the data is
+ * near-random and all the matches have very short lengths. Note that
+ * since this requires unaligned memory accesses, it won't necessarily
+ * be faster on every architecture.
+ *
+ * Also note that we might copy more than the length of the match. For
+ * example, if an 'unsigned long' is 8 bytes and the match is of length
+ * 5, then we'll simply copy 8 bytes. This is okay as long as we don't
+ * write beyond the end of the output buffer, hence the check for
+ * (winend - (dst + length) >= sizeof(unsigned long) - 1). */
+ if (offset >= sizeof(unsigned long) &&
+ winend - (dst + length) >= sizeof(unsigned long) - 1)
+ {
+ /* Access memory through a packed struct. This tricks the
+ * compiler into allowing unaligned memory accesses. */
+ struct ulong_wrapper {
+ unsigned long v;
+ } _packed_attribute;
+
+ const u8 *end = dst + length;
+ do {
+ unsigned long v = ((struct ulong_wrapper *)src)->v;
+ ((struct ulong_wrapper *)dst)->v = v;
+ dst += sizeof(unsigned long);
+ src += sizeof(unsigned long);
+ } while (dst < end);
+
+ return;
+ }
+#endif
+ do {
+ *dst++ = *src++;
+ } while (--length);
+}
+
+#endif /* _WIMLIB_DECOMPRESS_COMMON_H */