#include "wimlib/assert.h"
#include "wimlib/compiler.h"
-#include "wimlib/error.h"
#include "wimlib/endianness.h"
#include "wimlib/types.h"
istream->data_bytes_left = num_data_bytes;
}
-/* Ensures that the bit buffer variable for the bitstream contains @num_bits
- * bits.
+/* Ensures the bit buffer variable for the bitstream contains at least @num_bits
+ * bits. Following this, bitstream_peek_bits() and/or bitstream_remove_bits()
+ * may be called on the bitstream to peek or remove up to @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
+ * If the input data is exhausted, any further bits are assumed to be 0. */
+static inline void
bitstream_ensure_bits(struct input_bitstream *istream, unsigned num_bits)
{
for (int nbits = num_bits; (int)istream->bitsleft < nbits; nbits -= 16) {
u16 nextword;
unsigned shift;
- if (unlikely(istream->data_bytes_left < 2))
- return -1;
-
- wimlib_assert2(istream->bitsleft <= sizeof(istream->bitbuf) * 8 - 16);
+ if (unlikely(istream->data_bytes_left < 2)) {
+ istream->bitsleft = num_bits;
+ return;
+ }
nextword = le16_to_cpu(*(const le16*)istream->data);
shift = sizeof(istream->bitbuf) * 8 - 16 - istream->bitsleft;
istream->data += 2;
istream->bitsleft += 16;
istream->data_bytes_left -= 2;
-
}
- return 0;
}
-/* Returns the next @num_bits bits in the buffer variable, which must contain at
- * least @num_bits bits, for the bitstream. */
+/* Returns the next @num_bits bits from the bitstream, without removing them.
+ * There must be at least @num_bits remaining in the buffer variable, from a
+ * previous call to bitstream_ensure_bits(). */
static inline u32
bitstream_peek_bits(const struct input_bitstream *istream, unsigned num_bits)
{
- wimlib_assert2(istream->bitsleft >= num_bits);
-
if (unlikely(num_bits == 0))
return 0;
-
return istream->bitbuf >> (sizeof(istream->bitbuf) * 8 - num_bits);
}
-/* Removes @num_bits bits from the buffer variable, which must contain at least
- * @num_bits bits, for the bitstream. */
+/* Removes @num_bits from the bitstream. There must be at least @num_bits
+ * remaining in the buffer variable, from a previous call to
+ * bitstream_ensure_bits(). */
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;
}
-/* Gets and removes @num_bits bits from the buffer variable, which must contain
- * at least @num_bits bits, for the bitstream. */
+/* Removes and returns @num_bits bits from the bitstream. There must be at
+ * least @num_bits remaining in the buffer variable, from a previous call to
+ * bitstream_ensure_bits(). */
static inline u32
bitstream_pop_bits(struct input_bitstream *istream, unsigned num_bits)
{
return n;
}
-/* Reads @num_bits bits from the input bitstream. 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, u32 *n)
+/* Reads and returns the next @num_bits bits from the bitstream.
+ * If the input data is exhausted, the bits are assumed to be 0. */
+static inline u32
+bitstream_read_bits(struct input_bitstream *istream, unsigned num_bits)
{
- if (unlikely(bitstream_ensure_bits(istream, num_bits)))
- return -1;
-
- *n = bitstream_pop_bits(istream, num_bits);
- return 0;
+ bitstream_ensure_bits(istream, num_bits);
+ return bitstream_pop_bits(istream, num_bits);
}
-/* Return the next literal byte embedded in the bitstream, or -1 if the input
- * was exhausted. */
-static inline int
+/* Reads and returns the next literal byte embedded in the bitstream.
+ * If the input data is exhausted, the byte is assumed to be 0. */
+static inline u8
bitstream_read_byte(struct input_bitstream *istream)
{
- if (unlikely(istream->data_bytes_left < 1))
- return -1;
-
+ if (unlikely(istream->data_bytes_left == 0))
+ return 0;
istream->data_bytes_left--;
return *istream->data++;
}
-/* 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 u32
-bitstream_read_bits_nocheck(struct input_bitstream *istream, unsigned num_bits)
-{
- u32 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);
-
-/* Read a Huffman-encoded symbol from a bitstream. */
-static inline int
-read_huffsym(struct input_bitstream * restrict istream,
- const u16 decode_table[restrict],
- const u8 lens[restrict],
- unsigned num_syms,
- unsigned table_bits,
- unsigned *restrict n,
- unsigned max_codeword_len)
-{
- /* If there are fewer bits remaining in the input than the maximum
- * codeword length, use the slow path that has extra checks. */
- if (unlikely(bitstream_ensure_bits(istream, max_codeword_len))) {
- return read_huffsym_near_end_of_input(istream, decode_table,
- lens, num_syms,
- table_bits, n);
- }
-
- /* Use the next table_bits of the input as an index into the
- * decode_table. */
- u16 key_bits = bitstream_peek_bits(istream, table_bits);
+/* 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
- u16 sym = decode_table[key_bits];
+/* 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
- if (likely(sym < num_syms)) {
- /* Fast case: The decode table directly provided the symbol. */
- bitstream_remove_bits(istream, lens[sym]);
+/* 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.
+ *
+ * XXX: This is mostly duplicated in lzms_huffman_decode_symbol() in
+ * lzms-decompress.c. */
+static inline u16
+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);
+
+ /* 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_peek_bits(istream, 1);
- bitstream_remove_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;
}
- *n = sym;
- return 0;
}
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 */
+#endif /* _WIMLIB_DECOMPRESS_COMMON_H */
git://wimlib.net / wimlib / blobdiff