239 lines
9.3 KiB
C
239 lines
9.3 KiB
C
/*
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* jdhuff.h
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*
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* This file was part of the Independent JPEG Group's software:
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* Copyright (C) 1991-1997, Thomas G. Lane.
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* libjpeg-turbo Modifications:
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* Copyright (C) 2010-2011, 2015-2016, D. R. Commander.
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* For conditions of distribution and use, see the accompanying README.ijg
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* file.
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*
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* This file contains declarations for Huffman entropy decoding routines
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* that are shared between the sequential decoder (jdhuff.c) and the
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* progressive decoder (jdphuff.c). No other modules need to see these.
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*/
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#include "jconfigint.h"
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/* Derived data constructed for each Huffman table */
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#define HUFF_LOOKAHEAD 8 /* # of bits of lookahead */
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typedef struct {
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/* Basic tables: (element [0] of each array is unused) */
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JLONG maxcode[18]; /* largest code of length k (-1 if none) */
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/* (maxcode[17] is a sentinel to ensure jpeg_huff_decode terminates) */
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JLONG valoffset[18]; /* huffval[] offset for codes of length k */
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/* valoffset[k] = huffval[] index of 1st symbol of code length k, less
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* the smallest code of length k; so given a code of length k, the
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* corresponding symbol is huffval[code + valoffset[k]]
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*/
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/* Link to public Huffman table (needed only in jpeg_huff_decode) */
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JHUFF_TBL *pub;
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/* Lookahead table: indexed by the next HUFF_LOOKAHEAD bits of
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* the input data stream. If the next Huffman code is no more
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* than HUFF_LOOKAHEAD bits long, we can obtain its length and
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* the corresponding symbol directly from this tables.
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*
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* The lower 8 bits of each table entry contain the number of
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* bits in the corresponding Huffman code, or HUFF_LOOKAHEAD + 1
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* if too long. The next 8 bits of each entry contain the
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* symbol.
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*/
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int lookup[1 << HUFF_LOOKAHEAD];
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} d_derived_tbl;
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/* Expand a Huffman table definition into the derived format */
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EXTERN(void) jpeg_make_d_derived_tbl(j_decompress_ptr cinfo, boolean isDC,
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int tblno, d_derived_tbl **pdtbl);
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/*
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* Fetching the next N bits from the input stream is a time-critical operation
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* for the Huffman decoders. We implement it with a combination of inline
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* macros and out-of-line subroutines. Note that N (the number of bits
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* demanded at one time) never exceeds 15 for JPEG use.
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*
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* We read source bytes into get_buffer and dole out bits as needed.
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* If get_buffer already contains enough bits, they are fetched in-line
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* by the macros CHECK_BIT_BUFFER and GET_BITS. When there aren't enough
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* bits, jpeg_fill_bit_buffer is called; it will attempt to fill get_buffer
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* as full as possible (not just to the number of bits needed; this
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* prefetching reduces the overhead cost of calling jpeg_fill_bit_buffer).
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* Note that jpeg_fill_bit_buffer may return FALSE to indicate suspension.
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* On TRUE return, jpeg_fill_bit_buffer guarantees that get_buffer contains
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* at least the requested number of bits --- dummy zeroes are inserted if
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* necessary.
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*/
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#if !defined(_WIN32) && !defined(SIZEOF_SIZE_T)
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#error Cannot determine word size
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#endif
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#if SIZEOF_SIZE_T == 8 || defined(_WIN64)
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typedef size_t bit_buf_type; /* type of bit-extraction buffer */
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#define BIT_BUF_SIZE 64 /* size of buffer in bits */
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#else
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typedef unsigned long bit_buf_type; /* type of bit-extraction buffer */
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#define BIT_BUF_SIZE 32 /* size of buffer in bits */
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#endif
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/* If long is > 32 bits on your machine, and shifting/masking longs is
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* reasonably fast, making bit_buf_type be long and setting BIT_BUF_SIZE
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* appropriately should be a win. Unfortunately we can't define the size
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* with something like #define BIT_BUF_SIZE (sizeof(bit_buf_type)*8)
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* because not all machines measure sizeof in 8-bit bytes.
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*/
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typedef struct { /* Bitreading state saved across MCUs */
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bit_buf_type get_buffer; /* current bit-extraction buffer */
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int bits_left; /* # of unused bits in it */
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} bitread_perm_state;
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typedef struct { /* Bitreading working state within an MCU */
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/* Current data source location */
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/* We need a copy, rather than munging the original, in case of suspension */
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const JOCTET *next_input_byte; /* => next byte to read from source */
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size_t bytes_in_buffer; /* # of bytes remaining in source buffer */
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/* Bit input buffer --- note these values are kept in register variables,
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* not in this struct, inside the inner loops.
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*/
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bit_buf_type get_buffer; /* current bit-extraction buffer */
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int bits_left; /* # of unused bits in it */
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/* Pointer needed by jpeg_fill_bit_buffer. */
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j_decompress_ptr cinfo; /* back link to decompress master record */
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} bitread_working_state;
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/* Macros to declare and load/save bitread local variables. */
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#define BITREAD_STATE_VARS \
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register bit_buf_type get_buffer; \
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register int bits_left; \
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bitread_working_state br_state
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#define BITREAD_LOAD_STATE(cinfop, permstate) \
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br_state.cinfo = cinfop; \
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br_state.next_input_byte = cinfop->src->next_input_byte; \
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br_state.bytes_in_buffer = cinfop->src->bytes_in_buffer; \
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get_buffer = permstate.get_buffer; \
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bits_left = permstate.bits_left;
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#define BITREAD_SAVE_STATE(cinfop, permstate) \
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cinfop->src->next_input_byte = br_state.next_input_byte; \
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cinfop->src->bytes_in_buffer = br_state.bytes_in_buffer; \
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permstate.get_buffer = get_buffer; \
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permstate.bits_left = bits_left
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/*
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* These macros provide the in-line portion of bit fetching.
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* Use CHECK_BIT_BUFFER to ensure there are N bits in get_buffer
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* before using GET_BITS, PEEK_BITS, or DROP_BITS.
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* The variables get_buffer and bits_left are assumed to be locals,
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* but the state struct might not be (jpeg_huff_decode needs this).
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* CHECK_BIT_BUFFER(state, n, action);
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* Ensure there are N bits in get_buffer; if suspend, take action.
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* val = GET_BITS(n);
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* Fetch next N bits.
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* val = PEEK_BITS(n);
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* Fetch next N bits without removing them from the buffer.
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* DROP_BITS(n);
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* Discard next N bits.
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* The value N should be a simple variable, not an expression, because it
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* is evaluated multiple times.
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*/
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#define CHECK_BIT_BUFFER(state, nbits, action) { \
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if (bits_left < (nbits)) { \
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if (!jpeg_fill_bit_buffer(&(state), get_buffer, bits_left, nbits)) \
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{ action; } \
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get_buffer = (state).get_buffer; bits_left = (state).bits_left; \
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} \
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}
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#define GET_BITS(nbits) \
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(((int)(get_buffer >> (bits_left -= (nbits)))) & ((1 << (nbits)) - 1))
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#define PEEK_BITS(nbits) \
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(((int)(get_buffer >> (bits_left - (nbits)))) & ((1 << (nbits)) - 1))
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#define DROP_BITS(nbits) \
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(bits_left -= (nbits))
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/* Load up the bit buffer to a depth of at least nbits */
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EXTERN(boolean) jpeg_fill_bit_buffer(bitread_working_state *state,
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register bit_buf_type get_buffer,
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register int bits_left, int nbits);
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/*
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* Code for extracting next Huffman-coded symbol from input bit stream.
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* Again, this is time-critical and we make the main paths be macros.
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*
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* We use a lookahead table to process codes of up to HUFF_LOOKAHEAD bits
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* without looping. Usually, more than 95% of the Huffman codes will be 8
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* or fewer bits long. The few overlength codes are handled with a loop,
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* which need not be inline code.
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*
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* Notes about the HUFF_DECODE macro:
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* 1. Near the end of the data segment, we may fail to get enough bits
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* for a lookahead. In that case, we do it the hard way.
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* 2. If the lookahead table contains no entry, the next code must be
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* more than HUFF_LOOKAHEAD bits long.
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* 3. jpeg_huff_decode returns -1 if forced to suspend.
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*/
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#define HUFF_DECODE(result, state, htbl, failaction, slowlabel) { \
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register int nb, look; \
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if (bits_left < HUFF_LOOKAHEAD) { \
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if (!jpeg_fill_bit_buffer(&state, get_buffer, bits_left, 0)) \
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{ failaction; } \
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get_buffer = state.get_buffer; bits_left = state.bits_left; \
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if (bits_left < HUFF_LOOKAHEAD) { \
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nb = 1; goto slowlabel; \
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} \
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} \
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look = PEEK_BITS(HUFF_LOOKAHEAD); \
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if ((nb = (htbl->lookup[look] >> HUFF_LOOKAHEAD)) <= HUFF_LOOKAHEAD) { \
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DROP_BITS(nb); \
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result = htbl->lookup[look] & ((1 << HUFF_LOOKAHEAD) - 1); \
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} else { \
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slowlabel: \
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if ((result = \
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jpeg_huff_decode(&state, get_buffer, bits_left, htbl, nb)) < 0) \
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{ failaction; } \
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get_buffer = state.get_buffer; bits_left = state.bits_left; \
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} \
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}
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#define HUFF_DECODE_FAST(s, nb, htbl) \
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FILL_BIT_BUFFER_FAST; \
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s = PEEK_BITS(HUFF_LOOKAHEAD); \
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s = htbl->lookup[s]; \
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nb = s >> HUFF_LOOKAHEAD; \
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/* Pre-execute the common case of nb <= HUFF_LOOKAHEAD */ \
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DROP_BITS(nb); \
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s = s & ((1 << HUFF_LOOKAHEAD) - 1); \
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if (nb > HUFF_LOOKAHEAD) { \
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/* Equivalent of jpeg_huff_decode() */ \
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/* Don't use GET_BITS() here because we don't want to modify bits_left */ \
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s = (get_buffer >> bits_left) & ((1 << (nb)) - 1); \
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while (s > htbl->maxcode[nb]) { \
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s <<= 1; \
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s |= GET_BITS(1); \
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nb++; \
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} \
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s = htbl->pub->huffval[(int)(s + htbl->valoffset[nb]) & 0xFF]; \
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}
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/* Out-of-line case for Huffman code fetching */
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EXTERN(int) jpeg_huff_decode(bitread_working_state *state,
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register bit_buf_type get_buffer,
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register int bits_left, d_derived_tbl *htbl,
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int min_bits);
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