--- /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 provide a bitstream. */
+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; 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 contains @num_bits bits. */
+static inline int bitstream_ensure_bits(struct input_bitstream *istream,
+ unsigned num_bits)
+{
+ wimlib_assert(num_bits <= 16);
+
+ /* 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
+ while (istream->bitsleft < 16) {
+#else
+ while (istream->bitsleft < num_bits) {
+#endif
+ if (istream->data_bytes_left < 2)
+ return 1;
+
+ 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;
+ }
+ return 0;
+}
+
+/* Returns the next @num_bits bits in the bit buffer. It must contain at least
+ * @num_bits bits to call this function. */
+static inline unsigned
+bitstream_peek_bits(const struct input_bitstream *istream, unsigned num_bits)
+{
+ if (num_bits == 0)
+ return 0;
+ return istream->bitbuf >> (sizeof(input_bitbuf_t) * 8 - num_bits);
+}
+
+/* Removes @num_bits bits from the bit buffer. It must contain at least
+ * @num_bits bits to call this function. */
+static inline void bitstream_remove_bits(struct input_bitstream *istream,
+ unsigned num_bits)
+{
+ istream->bitbuf <<= num_bits;
+ istream->bitsleft -= num_bits;
+}
+
+/* Reads and returns @num_bits bits from the input bitstream. */
+static inline int bitstream_read_bits(struct input_bitstream *istream,
+ unsigned num_bits, unsigned *n)
+{
+ int ret;
+ ret = bitstream_ensure_bits(istream, num_bits);
+ if (ret != 0) {
+ ERROR("bitstream_read_bits(): Input buffer exhausted");
+ return ret;
+ }
+ *n = bitstream_peek_bits(istream, num_bits);
+ bitstream_remove_bits(istream, num_bits);
+ return 0;
+}
+
+/* In the XPRESS format there can be literal length bytes embedded in the
+ * compressed 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 length byte in the input
+ * bitstream. Returns -1 if we are at the end of the bitstream. */
+static inline int bitstream_read_byte(struct input_bitstream *istream)
+{
+ wimlib_assert(istream->bitsleft < 32);
+
+ if (istream->data_bytes_left == 0) {
+ ERROR("bitstream_read_byte(): Input buffer exhausted");
+ return -1;
+ }
+ istream->data_bytes_left--;
+ return *istream->data++;
+}
+
+/* Reads @num_bits bits from the bit buffer 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;
+}
+
+/* Removes the bits that have been read into the bit buffer variable. */
+static inline void flush_input_bitstream(struct input_bitstream *istream)
+{
+ bitstream_remove_bits(istream, istream->bitsleft);
+ istream->bitsleft = 0;
+ istream->bitbuf = 0;
+}
+
+extern int bitstream_read_bytes(struct input_bitstream *istream, size_t n,
+ void *dest);
+
+extern int align_input_bitstream(struct input_bitstream *istream,
+ bool skip_word_if_aligned);
+
+extern int read_huffsym(struct input_bitstream *stream,
+ const u16 decode_table[],
+ const u8 lengths[],
+ unsigned num_symbols,
+ unsigned table_bits,
+ unsigned *n,
+ unsigned max_codeword_len);
+
+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