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