X-Git-Url: https://wimlib.net/git/?p=wimlib;a=blobdiff_plain;f=src%2Fdecompress.h;h=a2466456f90019ea1189252cb46cfbdd245246b6;hp=ae1c99becda88f81e77146d3957683d65743b575;hb=1bf2548cc5ad9e94951c43b8c223cec058d28294;hpb=a6f5add5e9811584ebd75591a6a25cb9686da9a8 diff --git a/src/decompress.h b/src/decompress.h index ae1c99be..a2466456 100644 --- a/src/decompress.h +++ b/src/decompress.h @@ -13,12 +13,16 @@ /* Must be at least 32 bits. */ typedef unsigned long input_bitbuf_t; -/* Structure to provide a bitstream. */ +/* Structure to encapsulate a block of in-memory data that is being interpreted + * as a stream of bits. + * + * This is geared specifically towards the XPRESS and LZX compression formats + * with regards to the actual ordering the bits within the byte sequence. */ 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. */ + * to low-order, and the next bit is always the high-order bit. */ input_bitbuf_t bitbuf; /* Pointer to the next byte to be retrieved from the input. */ @@ -41,7 +45,11 @@ static inline void init_input_bitstream(struct input_bitstream *istream, istream->data_bytes_left = num_data_bytes; } -/* Ensures that the bit buffer contains @num_bits bits. */ +/* Ensures that the bit buffer variable for the bitstream contains @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 bitstream_ensure_bits(struct input_bitstream *istream, unsigned num_bits) { @@ -70,15 +78,15 @@ static inline int bitstream_ensure_bits(struct input_bitstream *istream, istream->bitsleft += 16; istream->data_bytes_left -= 2; } else { - ret = 1; + ret = -1; } } wimlib_assert2(ret != 0 || istream->bitsleft >= num_bits); return ret; } -/* Returns the next @num_bits bits in the bit buffer. It must contain at least - * @num_bits bits to call this function. */ +/* Returns the next @num_bits bits in the buffer variable, which must contain at + * least @num_bits bits, for the bitstream. */ static inline unsigned bitstream_peek_bits(const struct input_bitstream *istream, unsigned num_bits) { @@ -91,8 +99,8 @@ bitstream_peek_bits(const struct input_bitstream *istream, unsigned num_bits) return ret; } -/* Removes @num_bits bits from the bit buffer. It must contain at least - * @num_bits bits to call this function. */ +/* Removes @num_bits bits from the buffer variable, which must contain at least + * @num_bits bits, for the bitstream. */ static inline void bitstream_remove_bits(struct input_bitstream *istream, unsigned num_bits) { @@ -101,10 +109,13 @@ static inline void bitstream_remove_bits(struct input_bitstream *istream, istream->bitsleft -= num_bits; } -/* Reads and returns @num_bits bits from the input bitstream. */ +/* Reads @num_bits bits from the input bitstream. @num_bits must be 16 or fewer. + * 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, unsigned *n) { + wimlib_assert2(num_bits <= 16); int ret = bitstream_ensure_bits(istream, num_bits); if (ret == 0) { *n = bitstream_peek_bits(istream, num_bits); @@ -115,14 +126,13 @@ static inline int bitstream_read_bits(struct input_bitstream *istream, return ret; } -/* 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. +/* In the XPRESS format there can be literal bytes embedded in the 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. */ + * This function returns the next such literal byte, or -1 if there are no more. + */ static inline int bitstream_read_byte(struct input_bitstream *istream) { wimlib_assert2(istream->bitsleft < 32); @@ -138,8 +148,8 @@ static inline int bitstream_read_byte(struct input_bitstream *istream) return ret; } -/* Reads @num_bits bits from the bit buffer without checking to see if that many - * bits are in the buffer or not. */ +/* 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 unsigned bitstream_read_bits_nocheck(struct input_bitstream *istream, unsigned num_bits) { @@ -148,23 +158,6 @@ bitstream_read_bits_nocheck(struct input_bitstream *istream, unsigned 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->bitbuf = 0; - wimlib_assert2(istream->bitsleft == 0); -} - -extern int bitstream_read_bytes(struct input_bitstream *istream, size_t n, - void *dest); - -/* Aligns the bitstream on a 16-bit boundary. */ -static inline void align_input_bitstream(struct input_bitstream *istream) -{ - bitstream_remove_bits(istream, istream->bitsleft & 15); -} - extern int read_huffsym_near_end_of_input(struct input_bitstream *istream, const u16 decode_table[], const u8 lens[], @@ -179,7 +172,7 @@ extern int read_huffsym_near_end_of_input(struct input_bitstream *istream, * large WIM file. I'm not sure it could be made much faster that it is, * especially since there isn't enough time to make a big table that allows * decoding multiple symbols per lookup. But if extracting files to a hard - * disk, the IO will be the bottleneck anyway. + * disk, the I/O will be the bottleneck anyway. * * @buf: The input buffer from which the symbol will be read. * @decode_table: The fast Huffman decoding table for the Huffman tree.