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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, D. R. Commander.
8  * For conditions of distribution and use, see the accompanying README file.
9  *
10  * This file contains declarations for Huffman entropy decoding routines
11  * that are shared between the sequential decoder (jdhuff.c) and the
12  * progressive decoder (jdphuff.c).  No other modules need to see these.
13  */
14 
15 
16 /* Derived data constructed for each Huffman table */
17 
18 #define HUFF_LOOKAHEAD  8       /* # of bits of lookahead */
19 
20 typedef struct {
21   /* Basic tables: (element [0] of each array is unused) */
22   INT32 maxcode[18];            /* largest code of length k (-1 if none) */
23   /* (maxcode[17] is a sentinel to ensure jpeg_huff_decode terminates) */
24   INT32 valoffset[18];          /* huffval[] offset for codes of length k */
25   /* valoffset[k] = huffval[] index of 1st symbol of code length k, less
26    * the smallest code of length k; so given a code of length k, the
27    * corresponding symbol is huffval[code + valoffset[k]]
28    */
29 
30   /* Link to public Huffman table (needed only in jpeg_huff_decode) */
31   JHUFF_TBL *pub;
32 
33   /* Lookahead table: indexed by the next HUFF_LOOKAHEAD bits of
34    * the input data stream.  If the next Huffman code is no more
35    * than HUFF_LOOKAHEAD bits long, we can obtain its length and
36    * the corresponding symbol directly from this tables.
37    *
38    * The lower 8 bits of each table entry contain the number of
39    * bits in the corresponding Huffman code, or HUFF_LOOKAHEAD + 1
40    * if too long.  The next 8 bits of each entry contain the
41    * symbol.
42    */
43   int lookup[1<<HUFF_LOOKAHEAD];
44 } d_derived_tbl;
45 
46 /* Expand a Huffman table definition into the derived format */
47 EXTERN(void) jpeg_make_d_derived_tbl
48         (j_decompress_ptr cinfo, boolean isDC, int tblno,
49          d_derived_tbl ** pdtbl);
50 
51 
52 /*
53  * Fetching the next N bits from the input stream is a time-critical operation
54  * for the Huffman decoders.  We implement it with a combination of inline
55  * macros and out-of-line subroutines.  Note that N (the number of bits
56  * demanded at one time) never exceeds 15 for JPEG use.
57  *
58  * We read source bytes into get_buffer and dole out bits as needed.
59  * If get_buffer already contains enough bits, they are fetched in-line
60  * by the macros CHECK_BIT_BUFFER and GET_BITS.  When there aren't enough
61  * bits, jpeg_fill_bit_buffer is called; it will attempt to fill get_buffer
62  * as full as possible (not just to the number of bits needed; this
63  * prefetching reduces the overhead cost of calling jpeg_fill_bit_buffer).
64  * Note that jpeg_fill_bit_buffer may return FALSE to indicate suspension.
65  * On TRUE return, jpeg_fill_bit_buffer guarantees that get_buffer contains
66  * at least the requested number of bits --- dummy zeroes are inserted if
67  * necessary.
68  */
69 
70 #if !defined(_WIN32) && !defined(SIZEOF_SIZE_T)
71 #error Cannot determine word size
72 #endif
73 
74 #if SIZEOF_SIZE_T==8 || defined(_WIN64)
75 
76 typedef size_t bit_buf_type;    /* type of bit-extraction buffer */
77 #define BIT_BUF_SIZE  64                /* size of buffer in bits */
78 
79 #else
80 
81 typedef INT32 bit_buf_type;     /* type of bit-extraction buffer */
82 #define BIT_BUF_SIZE  32                /* size of buffer in bits */
83 
84 #endif
85 
86 /* If long is > 32 bits on your machine, and shifting/masking longs is
87  * reasonably fast, making bit_buf_type be long and setting BIT_BUF_SIZE
88  * appropriately should be a win.  Unfortunately we can't define the size
89  * with something like  #define BIT_BUF_SIZE (sizeof(bit_buf_type)*8)
90  * because not all machines measure sizeof in 8-bit bytes.
91  */
92 
93 typedef struct {                /* Bitreading state saved across MCUs */
94   bit_buf_type get_buffer;      /* current bit-extraction buffer */
95   int bits_left;                /* # of unused bits in it */
96 } bitread_perm_state;
97 
98 typedef struct {                /* Bitreading working state within an MCU */
99   /* Current data source location */
100   /* We need a copy, rather than munging the original, in case of suspension */
101   const JOCTET * next_input_byte; /* => next byte to read from source */
102   size_t bytes_in_buffer;       /* # of bytes remaining in source buffer */
103   /* Bit input buffer --- note these values are kept in register variables,
104    * not in this struct, inside the inner loops.
105    */
106   bit_buf_type get_buffer;      /* current bit-extraction buffer */
107   int bits_left;                /* # of unused bits in it */
108   /* Pointer needed by jpeg_fill_bit_buffer. */
109   j_decompress_ptr cinfo;       /* back link to decompress master record */
110 } bitread_working_state;
111 
112 /* Macros to declare and load/save bitread local variables. */
113 #define BITREAD_STATE_VARS  \
114         register bit_buf_type get_buffer;  \
115         register int bits_left;  \
116         bitread_working_state br_state
117 
118 #define BITREAD_LOAD_STATE(cinfop,permstate)  \
119         br_state.cinfo = cinfop; \
120         br_state.next_input_byte = cinfop->src->next_input_byte; \
121         br_state.bytes_in_buffer = cinfop->src->bytes_in_buffer; \
122         get_buffer = permstate.get_buffer; \
123         bits_left = permstate.bits_left;
124 
125 #define BITREAD_SAVE_STATE(cinfop,permstate)  \
126         cinfop->src->next_input_byte = br_state.next_input_byte; \
127         cinfop->src->bytes_in_buffer = br_state.bytes_in_buffer; \
128         permstate.get_buffer = get_buffer; \
129         permstate.bits_left = bits_left
130 
131 /*
132  * These macros provide the in-line portion of bit fetching.
133  * Use CHECK_BIT_BUFFER to ensure there are N bits in get_buffer
134  * before using GET_BITS, PEEK_BITS, or DROP_BITS.
135  * The variables get_buffer and bits_left are assumed to be locals,
136  * but the state struct might not be (jpeg_huff_decode needs this).
137  *      CHECK_BIT_BUFFER(state,n,action);
138  *              Ensure there are N bits in get_buffer; if suspend, take action.
139  *      val = GET_BITS(n);
140  *              Fetch next N bits.
141  *      val = PEEK_BITS(n);
142  *              Fetch next N bits without removing them from the buffer.
143  *      DROP_BITS(n);
144  *              Discard next N bits.
145  * The value N should be a simple variable, not an expression, because it
146  * is evaluated multiple times.
147  */
148 
149 #define CHECK_BIT_BUFFER(state,nbits,action) \
150         { if (bits_left < (nbits)) {  \
151             if (! jpeg_fill_bit_buffer(&(state),get_buffer,bits_left,nbits))  \
152               { action; }  \
153             get_buffer = (state).get_buffer; bits_left = (state).bits_left; } }
154 
155 #define GET_BITS(nbits) \
156         (((int) (get_buffer >> (bits_left -= (nbits)))) & ((1<<(nbits))-1))
157 
158 #define PEEK_BITS(nbits) \
159         (((int) (get_buffer >> (bits_left -  (nbits)))) & ((1<<(nbits))-1))
160 
161 #define DROP_BITS(nbits) \
162         (bits_left -= (nbits))
163 
164 /* Load up the bit buffer to a depth of at least nbits */
165 EXTERN(boolean) jpeg_fill_bit_buffer
166         (bitread_working_state * state, register bit_buf_type get_buffer,
167          register int bits_left, int nbits);
168 
169 
170 /*
171  * Code for extracting next Huffman-coded symbol from input bit stream.
172  * Again, this is time-critical and we make the main paths be macros.
173  *
174  * We use a lookahead table to process codes of up to HUFF_LOOKAHEAD bits
175  * without looping.  Usually, more than 95% of the Huffman codes will be 8
176  * or fewer bits long.  The few overlength codes are handled with a loop,
177  * which need not be inline code.
178  *
179  * Notes about the HUFF_DECODE macro:
180  * 1. Near the end of the data segment, we may fail to get enough bits
181  *    for a lookahead.  In that case, we do it the hard way.
182  * 2. If the lookahead table contains no entry, the next code must be
183  *    more than HUFF_LOOKAHEAD bits long.
184  * 3. jpeg_huff_decode returns -1 if forced to suspend.
185  */
186 
187 #define HUFF_DECODE(result,state,htbl,failaction,slowlabel) \
188 { register int nb, look; \
189   if (bits_left < HUFF_LOOKAHEAD) { \
190     if (! jpeg_fill_bit_buffer(&state,get_buffer,bits_left, 0)) {failaction;} \
191     get_buffer = state.get_buffer; bits_left = state.bits_left; \
192     if (bits_left < HUFF_LOOKAHEAD) { \
193       nb = 1; goto slowlabel; \
194     } \
195   } \
196   look = PEEK_BITS(HUFF_LOOKAHEAD); \
197   if ((nb = (htbl->lookup[look] >> HUFF_LOOKAHEAD)) <= HUFF_LOOKAHEAD) { \
198     DROP_BITS(nb); \
199     result = htbl->lookup[look] & ((1 << HUFF_LOOKAHEAD) - 1); \
200   } else { \
201 slowlabel: \
202     if ((result=jpeg_huff_decode(&state,get_buffer,bits_left,htbl,nb)) < 0) \
203         { failaction; } \
204     get_buffer = state.get_buffer; bits_left = state.bits_left; \
205   } \
206 }
207 
208 #define HUFF_DECODE_FAST(s,nb,htbl) \
209   FILL_BIT_BUFFER_FAST; \
210   s = PEEK_BITS(HUFF_LOOKAHEAD); \
211   s = htbl->lookup[s]; \
212   nb = s >> HUFF_LOOKAHEAD; \
213   /* Pre-execute the common case of nb <= HUFF_LOOKAHEAD */ \
214   DROP_BITS(nb); \
215   s = s & ((1 << HUFF_LOOKAHEAD) - 1); \
216   if (nb > HUFF_LOOKAHEAD) { \
217     /* Equivalent of jpeg_huff_decode() */ \
218     /* Don't use GET_BITS() here because we don't want to modify bits_left */ \
219     s = (get_buffer >> bits_left) & ((1 << (nb)) - 1); \
220     while (s > htbl->maxcode[nb]) { \
221       s <<= 1; \
222       s |= GET_BITS(1); \
223       nb++; \
224     } \
225     s = htbl->pub->huffval[ (int) (s + htbl->valoffset[nb]) & 0xFF ]; \
226   }
227 
228 /* Out-of-line case for Huffman code fetching */
229 EXTERN(int) jpeg_huff_decode
230         (bitread_working_state * state, register bit_buf_type get_buffer,
231          register int bits_left, d_derived_tbl * htbl, int min_bits);
232