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
+/* 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. */
+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 *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);
- }
+
+ bitstream_ensure_bits(istream, max_codeword_len);
/* Use the next table_bits of the input as an index into the
* decode_table. */
* end of the decode table. */
bitstream_remove_bits(istream, table_bits);
do {
- key_bits = sym + bitstream_peek_bits(istream, 1);
- bitstream_remove_bits(istream, 1);
+ key_bits = sym + bitstream_pop_bits(istream, 1);
} while ((sym = decode_table[key_bits]) >= num_syms);
}
- *n = sym;
- return 0;
+ return sym;
}
extern int
git://wimlib.net / wimlib / blobdiff