1 | /* |
2 | * jdhuff.h |
3 | * |
4 | * This file was part of the Independent JPEG Group's software: |
5 | * Copyright (C) 1991-1997, Thomas G. Lane. |
6 | * libjpeg-turbo Modifications: |
7 | * Copyright (C) 2010-2011, 2015-2016, 2021, D. R. Commander. |
8 | * Copyright (C) 2018, Matthias Räncker. |
9 | * For conditions of distribution and use, see the accompanying README.ijg |
10 | * file. |
11 | * |
12 | * This file contains declarations for Huffman entropy decoding routines |
13 | * that are shared between the sequential decoder (jdhuff.c) and the |
14 | * progressive decoder (jdphuff.c). No other modules need to see these. |
15 | */ |
16 | |
17 | #include "jconfigint.h" |
18 | |
19 | |
20 | /* Derived data constructed for each Huffman table */ |
21 | |
22 | #define HUFF_LOOKAHEAD 8 /* # of bits of lookahead */ |
23 | |
24 | typedef struct { |
25 | /* Basic tables: (element [0] of each array is unused) */ |
26 | JLONG maxcode[18]; /* largest code of length k (-1 if none) */ |
27 | /* (maxcode[17] is a sentinel to ensure jpeg_huff_decode terminates) */ |
28 | JLONG valoffset[18]; /* huffval[] offset for codes of length k */ |
29 | /* valoffset[k] = huffval[] index of 1st symbol of code length k, less |
30 | * the smallest code of length k; so given a code of length k, the |
31 | * corresponding symbol is huffval[code + valoffset[k]] |
32 | */ |
33 | |
34 | /* Link to public Huffman table (needed only in jpeg_huff_decode) */ |
35 | JHUFF_TBL *pub; |
36 | |
37 | /* Lookahead table: indexed by the next HUFF_LOOKAHEAD bits of |
38 | * the input data stream. If the next Huffman code is no more |
39 | * than HUFF_LOOKAHEAD bits long, we can obtain its length and |
40 | * the corresponding symbol directly from this tables. |
41 | * |
42 | * The lower 8 bits of each table entry contain the number of |
43 | * bits in the corresponding Huffman code, or HUFF_LOOKAHEAD + 1 |
44 | * if too long. The next 8 bits of each entry contain the |
45 | * symbol. |
46 | */ |
47 | int lookup[1 << HUFF_LOOKAHEAD]; |
48 | } d_derived_tbl; |
49 | |
50 | /* Expand a Huffman table definition into the derived format */ |
51 | EXTERN(void) jpeg_make_d_derived_tbl(j_decompress_ptr cinfo, boolean isDC, |
52 | int tblno, d_derived_tbl **pdtbl); |
53 | |
54 | |
55 | /* |
56 | * Fetching the next N bits from the input stream is a time-critical operation |
57 | * for the Huffman decoders. We implement it with a combination of inline |
58 | * macros and out-of-line subroutines. Note that N (the number of bits |
59 | * demanded at one time) never exceeds 15 for JPEG use. |
60 | * |
61 | * We read source bytes into get_buffer and dole out bits as needed. |
62 | * If get_buffer already contains enough bits, they are fetched in-line |
63 | * by the macros CHECK_BIT_BUFFER and GET_BITS. When there aren't enough |
64 | * bits, jpeg_fill_bit_buffer is called; it will attempt to fill get_buffer |
65 | * as full as possible (not just to the number of bits needed; this |
66 | * prefetching reduces the overhead cost of calling jpeg_fill_bit_buffer). |
67 | * Note that jpeg_fill_bit_buffer may return FALSE to indicate suspension. |
68 | * On TRUE return, jpeg_fill_bit_buffer guarantees that get_buffer contains |
69 | * at least the requested number of bits --- dummy zeroes are inserted if |
70 | * necessary. |
71 | */ |
72 | |
73 | #if !defined(_WIN32) && !defined(SIZEOF_SIZE_T) |
74 | #error Cannot determine word size |
75 | #endif |
76 | |
77 | #if SIZEOF_SIZE_T == 8 || defined(_WIN64) |
78 | |
79 | typedef size_t bit_buf_type; /* type of bit-extraction buffer */ |
80 | #define BIT_BUF_SIZE 64 /* size of buffer in bits */ |
81 | |
82 | #elif defined(__x86_64__) && defined(__ILP32__) |
83 | |
84 | typedef unsigned long long bit_buf_type; /* type of bit-extraction buffer */ |
85 | #define BIT_BUF_SIZE 64 /* size of buffer in bits */ |
86 | |
87 | #else |
88 | |
89 | typedef unsigned long bit_buf_type; /* type of bit-extraction buffer */ |
90 | #define BIT_BUF_SIZE 32 /* size of buffer in bits */ |
91 | |
92 | #endif |
93 | |
94 | /* If long is > 32 bits on your machine, and shifting/masking longs is |
95 | * reasonably fast, making bit_buf_type be long and setting BIT_BUF_SIZE |
96 | * appropriately should be a win. Unfortunately we can't define the size |
97 | * with something like #define BIT_BUF_SIZE (sizeof(bit_buf_type)*8) |
98 | * because not all machines measure sizeof in 8-bit bytes. |
99 | */ |
100 | |
101 | typedef struct { /* Bitreading state saved across MCUs */ |
102 | bit_buf_type get_buffer; /* current bit-extraction buffer */ |
103 | int bits_left; /* # of unused bits in it */ |
104 | } bitread_perm_state; |
105 | |
106 | typedef struct { /* Bitreading working state within an MCU */ |
107 | /* Current data source location */ |
108 | /* We need a copy, rather than munging the original, in case of suspension */ |
109 | const JOCTET *next_input_byte; /* => next byte to read from source */ |
110 | size_t bytes_in_buffer; /* # of bytes remaining in source buffer */ |
111 | /* Bit input buffer --- note these values are kept in register variables, |
112 | * not in this struct, inside the inner loops. |
113 | */ |
114 | bit_buf_type get_buffer; /* current bit-extraction buffer */ |
115 | int bits_left; /* # of unused bits in it */ |
116 | /* Pointer needed by jpeg_fill_bit_buffer. */ |
117 | j_decompress_ptr cinfo; /* back link to decompress master record */ |
118 | } bitread_working_state; |
119 | |
120 | /* Macros to declare and load/save bitread local variables. */ |
121 | #define BITREAD_STATE_VARS \ |
122 | register bit_buf_type get_buffer; \ |
123 | register int bits_left; \ |
124 | bitread_working_state br_state |
125 | |
126 | #define BITREAD_LOAD_STATE(cinfop, permstate) \ |
127 | br_state.cinfo = cinfop; \ |
128 | br_state.next_input_byte = cinfop->src->next_input_byte; \ |
129 | br_state.bytes_in_buffer = cinfop->src->bytes_in_buffer; \ |
130 | get_buffer = permstate.get_buffer; \ |
131 | bits_left = permstate.bits_left; |
132 | |
133 | #define BITREAD_SAVE_STATE(cinfop, permstate) \ |
134 | cinfop->src->next_input_byte = br_state.next_input_byte; \ |
135 | cinfop->src->bytes_in_buffer = br_state.bytes_in_buffer; \ |
136 | permstate.get_buffer = get_buffer; \ |
137 | permstate.bits_left = bits_left |
138 | |
139 | /* |
140 | * These macros provide the in-line portion of bit fetching. |
141 | * Use CHECK_BIT_BUFFER to ensure there are N bits in get_buffer |
142 | * before using GET_BITS, PEEK_BITS, or DROP_BITS. |
143 | * The variables get_buffer and bits_left are assumed to be locals, |
144 | * but the state struct might not be (jpeg_huff_decode needs this). |
145 | * CHECK_BIT_BUFFER(state, n, action); |
146 | * Ensure there are N bits in get_buffer; if suspend, take action. |
147 | * val = GET_BITS(n); |
148 | * Fetch next N bits. |
149 | * val = PEEK_BITS(n); |
150 | * Fetch next N bits without removing them from the buffer. |
151 | * DROP_BITS(n); |
152 | * Discard next N bits. |
153 | * The value N should be a simple variable, not an expression, because it |
154 | * is evaluated multiple times. |
155 | */ |
156 | |
157 | #define CHECK_BIT_BUFFER(state, nbits, action) { \ |
158 | if (bits_left < (nbits)) { \ |
159 | if (!jpeg_fill_bit_buffer(&(state), get_buffer, bits_left, nbits)) \ |
160 | { action; } \ |
161 | get_buffer = (state).get_buffer; bits_left = (state).bits_left; \ |
162 | } \ |
163 | } |
164 | |
165 | #define GET_BITS(nbits) \ |
166 | (((int)(get_buffer >> (bits_left -= (nbits)))) & ((1 << (nbits)) - 1)) |
167 | |
168 | #define PEEK_BITS(nbits) \ |
169 | (((int)(get_buffer >> (bits_left - (nbits)))) & ((1 << (nbits)) - 1)) |
170 | |
171 | #define DROP_BITS(nbits) \ |
172 | (bits_left -= (nbits)) |
173 | |
174 | /* Load up the bit buffer to a depth of at least nbits */ |
175 | EXTERN(boolean) jpeg_fill_bit_buffer(bitread_working_state *state, |
176 | register bit_buf_type get_buffer, |
177 | register int bits_left, int nbits); |
178 | |
179 | |
180 | /* |
181 | * Code for extracting next Huffman-coded symbol from input bit stream. |
182 | * Again, this is time-critical and we make the main paths be macros. |
183 | * |
184 | * We use a lookahead table to process codes of up to HUFF_LOOKAHEAD bits |
185 | * without looping. Usually, more than 95% of the Huffman codes will be 8 |
186 | * or fewer bits long. The few overlength codes are handled with a loop, |
187 | * which need not be inline code. |
188 | * |
189 | * Notes about the HUFF_DECODE macro: |
190 | * 1. Near the end of the data segment, we may fail to get enough bits |
191 | * for a lookahead. In that case, we do it the hard way. |
192 | * 2. If the lookahead table contains no entry, the next code must be |
193 | * more than HUFF_LOOKAHEAD bits long. |
194 | * 3. jpeg_huff_decode returns -1 if forced to suspend. |
195 | */ |
196 | |
197 | #define HUFF_DECODE(result, state, htbl, failaction, slowlabel) { \ |
198 | register int nb, look; \ |
199 | if (bits_left < HUFF_LOOKAHEAD) { \ |
200 | if (!jpeg_fill_bit_buffer(&state, get_buffer, bits_left, 0)) \ |
201 | { failaction; } \ |
202 | get_buffer = state.get_buffer; bits_left = state.bits_left; \ |
203 | if (bits_left < HUFF_LOOKAHEAD) { \ |
204 | nb = 1; goto slowlabel; \ |
205 | } \ |
206 | } \ |
207 | look = PEEK_BITS(HUFF_LOOKAHEAD); \ |
208 | if ((nb = (htbl->lookup[look] >> HUFF_LOOKAHEAD)) <= HUFF_LOOKAHEAD) { \ |
209 | DROP_BITS(nb); \ |
210 | result = htbl->lookup[look] & ((1 << HUFF_LOOKAHEAD) - 1); \ |
211 | } else { \ |
212 | slowlabel: \ |
213 | if ((result = \ |
214 | jpeg_huff_decode(&state, get_buffer, bits_left, htbl, nb)) < 0) \ |
215 | { failaction; } \ |
216 | get_buffer = state.get_buffer; bits_left = state.bits_left; \ |
217 | } \ |
218 | } |
219 | |
220 | #define HUFF_DECODE_FAST(s, nb, htbl) \ |
221 | FILL_BIT_BUFFER_FAST; \ |
222 | s = PEEK_BITS(HUFF_LOOKAHEAD); \ |
223 | s = htbl->lookup[s]; \ |
224 | nb = s >> HUFF_LOOKAHEAD; \ |
225 | /* Pre-execute the common case of nb <= HUFF_LOOKAHEAD */ \ |
226 | DROP_BITS(nb); \ |
227 | s = s & ((1 << HUFF_LOOKAHEAD) - 1); \ |
228 | if (nb > HUFF_LOOKAHEAD) { \ |
229 | /* Equivalent of jpeg_huff_decode() */ \ |
230 | /* Don't use GET_BITS() here because we don't want to modify bits_left */ \ |
231 | s = (get_buffer >> bits_left) & ((1 << (nb)) - 1); \ |
232 | while (s > htbl->maxcode[nb]) { \ |
233 | s <<= 1; \ |
234 | s |= GET_BITS(1); \ |
235 | nb++; \ |
236 | } \ |
237 | if (nb > 16) \ |
238 | s = 0; \ |
239 | else \ |
240 | s = htbl->pub->huffval[(int)(s + htbl->valoffset[nb]) & 0xFF]; \ |
241 | } |
242 | |
243 | /* Out-of-line case for Huffman code fetching */ |
244 | EXTERN(int) jpeg_huff_decode(bitread_working_state *state, |
245 | register bit_buf_type get_buffer, |
246 | register int bits_left, d_derived_tbl *htbl, |
247 | int min_bits); |
248 | |