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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  * 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 /* Short forms of external names for systems with brain-damaged linkers. */
16 
17 #ifdef NEED_SHORT_EXTERNAL_NAMES
18 #define jpeg_make_d_derived_tbl	jMkDDerived
19 #define jpeg_fill_bit_buffer	jFilBitBuf
20 #define jpeg_huff_decode	jHufDecode
21 #endif /* NEED_SHORT_EXTERNAL_NAMES */
22 
23 
24 /* Derived data constructed for each Huffman table */
25 
26 #define HUFF_LOOKAHEAD	8	/* # of bits of lookahead */
27 
28 typedef struct {
29   /* Basic tables: (element [0] of each array is unused) */
30   INT32 maxcode[18];		/* largest code of length k (-1 if none) */
31   /* (maxcode[17] is a sentinel to ensure jpeg_huff_decode terminates) */
32   INT32 valoffset[18];		/* huffval[] offset for codes of length k */
33   /* valoffset[k] = huffval[] index of 1st symbol of code length k, less
34    * the smallest code of length k; so given a code of length k, the
35    * corresponding symbol is huffval[code + valoffset[k]]
36    */
37 
38   /* Link to public Huffman table (needed only in jpeg_huff_decode) */
39   JHUFF_TBL *pub;
40 
41   /* Lookahead table: indexed by the next HUFF_LOOKAHEAD bits of
42    * the input data stream.  If the next Huffman code is no more
43    * than HUFF_LOOKAHEAD bits long, we can obtain its length and
44    * the corresponding symbol directly from this tables.
45    *
46    * The lower 8 bits of each table entry contain the number of
47    * bits in the corresponding Huffman code, or HUFF_LOOKAHEAD + 1
48    * if too long.  The next 8 bits of each entry contain the
49    * symbol.
50    */
51   int lookup[1<<HUFF_LOOKAHEAD];
52 } d_derived_tbl;
53 
54 /* Expand a Huffman table definition into the derived format */
55 EXTERN(void) jpeg_make_d_derived_tbl
56 	JPP((j_decompress_ptr cinfo, boolean isDC, int tblno,
57 	     d_derived_tbl ** pdtbl));
58 
59 
60 /*
61  * Fetching the next N bits from the input stream is a time-critical operation
62  * for the Huffman decoders.  We implement it with a combination of inline
63  * macros and out-of-line subroutines.  Note that N (the number of bits
64  * demanded at one time) never exceeds 15 for JPEG use.
65  *
66  * We read source bytes into get_buffer and dole out bits as needed.
67  * If get_buffer already contains enough bits, they are fetched in-line
68  * by the macros CHECK_BIT_BUFFER and GET_BITS.  When there aren't enough
69  * bits, jpeg_fill_bit_buffer is called; it will attempt to fill get_buffer
70  * as full as possible (not just to the number of bits needed; this
71  * prefetching reduces the overhead cost of calling jpeg_fill_bit_buffer).
72  * Note that jpeg_fill_bit_buffer may return FALSE to indicate suspension.
73  * On TRUE return, jpeg_fill_bit_buffer guarantees that get_buffer contains
74  * at least the requested number of bits --- dummy zeroes are inserted if
75  * necessary.
76  */
77 
78 #if __WORDSIZE == 64 || defined(_WIN64)
79 
80 typedef size_t bit_buf_type;	/* type of bit-extraction buffer */
81 #define BIT_BUF_SIZE  64		/* size of buffer in bits */
82 
83 #else
84 
85 typedef INT32 bit_buf_type;	/* type of bit-extraction buffer */
86 #define BIT_BUF_SIZE  32		/* size of buffer in bits */
87 
88 #endif
89 
90 /* If long is > 32 bits on your machine, and shifting/masking longs is
91  * reasonably fast, making bit_buf_type be long and setting BIT_BUF_SIZE
92  * appropriately should be a win.  Unfortunately we can't define the size
93  * with something like  #define BIT_BUF_SIZE (sizeof(bit_buf_type)*8)
94  * because not all machines measure sizeof in 8-bit bytes.
95  */
96 
97 typedef struct {		/* Bitreading state saved across MCUs */
98   bit_buf_type get_buffer;	/* current bit-extraction buffer */
99   int bits_left;		/* # of unused bits in it */
100 } bitread_perm_state;
101 
102 typedef struct {		/* Bitreading working state within an MCU */
103   /* Current data source location */
104   /* We need a copy, rather than munging the original, in case of suspension */
105   const JOCTET * next_input_byte; /* => next byte to read from source */
106   size_t bytes_in_buffer;	/* # of bytes remaining in source buffer */
107   /* Bit input buffer --- note these values are kept in register variables,
108    * not in this struct, inside the inner loops.
109    */
110   bit_buf_type get_buffer;	/* current bit-extraction buffer */
111   int bits_left;		/* # of unused bits in it */
112   /* Pointer needed by jpeg_fill_bit_buffer. */
113   j_decompress_ptr cinfo;	/* back link to decompress master record */
114 } bitread_working_state;
115 
116 /* Macros to declare and load/save bitread local variables. */
117 #define BITREAD_STATE_VARS  \
118 	register bit_buf_type get_buffer;  \
119 	register int bits_left;  \
120 	bitread_working_state br_state
121 
122 #define BITREAD_LOAD_STATE(cinfop,permstate)  \
123 	br_state.cinfo = cinfop; \
124 	br_state.next_input_byte = cinfop->src->next_input_byte; \
125 	br_state.bytes_in_buffer = cinfop->src->bytes_in_buffer; \
126 	get_buffer = permstate.get_buffer; \
127 	bits_left = permstate.bits_left;
128 
129 #define BITREAD_SAVE_STATE(cinfop,permstate)  \
130 	cinfop->src->next_input_byte = br_state.next_input_byte; \
131 	cinfop->src->bytes_in_buffer = br_state.bytes_in_buffer; \
132 	permstate.get_buffer = get_buffer; \
133 	permstate.bits_left = bits_left
134 
135 /*
136  * These macros provide the in-line portion of bit fetching.
137  * Use CHECK_BIT_BUFFER to ensure there are N bits in get_buffer
138  * before using GET_BITS, PEEK_BITS, or DROP_BITS.
139  * The variables get_buffer and bits_left are assumed to be locals,
140  * but the state struct might not be (jpeg_huff_decode needs this).
141  *	CHECK_BIT_BUFFER(state,n,action);
142  *		Ensure there are N bits in get_buffer; if suspend, take action.
143  *      val = GET_BITS(n);
144  *		Fetch next N bits.
145  *      val = PEEK_BITS(n);
146  *		Fetch next N bits without removing them from the buffer.
147  *	DROP_BITS(n);
148  *		Discard next N bits.
149  * The value N should be a simple variable, not an expression, because it
150  * is evaluated multiple times.
151  */
152 
153 #define CHECK_BIT_BUFFER(state,nbits,action) \
154 	{ if (bits_left < (nbits)) {  \
155 	    if (! jpeg_fill_bit_buffer(&(state),get_buffer,bits_left,nbits))  \
156 	      { action; }  \
157 	    get_buffer = (state).get_buffer; bits_left = (state).bits_left; } }
158 
159 #define GET_BITS(nbits) \
160 	(((int) (get_buffer >> (bits_left -= (nbits)))) & ((1<<(nbits))-1))
161 
162 #define PEEK_BITS(nbits) \
163 	(((int) (get_buffer >> (bits_left -  (nbits)))) & ((1<<(nbits))-1))
164 
165 #define DROP_BITS(nbits) \
166 	(bits_left -= (nbits))
167 
168 /* Load up the bit buffer to a depth of at least nbits */
169 EXTERN(boolean) jpeg_fill_bit_buffer
170 	JPP((bitread_working_state * state, register bit_buf_type get_buffer,
171 	     register int bits_left, int nbits));
172 
173 
174 /*
175  * Code for extracting next Huffman-coded symbol from input bit stream.
176  * Again, this is time-critical and we make the main paths be macros.
177  *
178  * We use a lookahead table to process codes of up to HUFF_LOOKAHEAD bits
179  * without looping.  Usually, more than 95% of the Huffman codes will be 8
180  * or fewer bits long.  The few overlength codes are handled with a loop,
181  * which need not be inline code.
182  *
183  * Notes about the HUFF_DECODE macro:
184  * 1. Near the end of the data segment, we may fail to get enough bits
185  *    for a lookahead.  In that case, we do it the hard way.
186  * 2. If the lookahead table contains no entry, the next code must be
187  *    more than HUFF_LOOKAHEAD bits long.
188  * 3. jpeg_huff_decode returns -1 if forced to suspend.
189  */
190 
191 #define HUFF_DECODE(result,state,htbl,failaction,slowlabel) \
192 { register int nb, look; \
193   if (bits_left < HUFF_LOOKAHEAD) { \
194     if (! jpeg_fill_bit_buffer(&state,get_buffer,bits_left, 0)) {failaction;} \
195     get_buffer = state.get_buffer; bits_left = state.bits_left; \
196     if (bits_left < HUFF_LOOKAHEAD) { \
197       nb = 1; goto slowlabel; \
198     } \
199   } \
200   look = PEEK_BITS(HUFF_LOOKAHEAD); \
201   if ((nb = (htbl->lookup[look] >> HUFF_LOOKAHEAD)) <= HUFF_LOOKAHEAD) { \
202     DROP_BITS(nb); \
203     result = htbl->lookup[look] & ((1 << HUFF_LOOKAHEAD) - 1); \
204   } else { \
205 slowlabel: \
206     if ((result=jpeg_huff_decode(&state,get_buffer,bits_left,htbl,nb)) < 0) \
207 	{ failaction; } \
208     get_buffer = state.get_buffer; bits_left = state.bits_left; \
209   } \
210 }
211 
212 #define HUFF_DECODE_FAST(s,nb,htbl) \
213   FILL_BIT_BUFFER_FAST; \
214   s = PEEK_BITS(HUFF_LOOKAHEAD); \
215   s = htbl->lookup[s]; \
216   nb = s >> HUFF_LOOKAHEAD; \
217   /* Pre-execute the common case of nb <= HUFF_LOOKAHEAD */ \
218   DROP_BITS(nb); \
219   s = s & ((1 << HUFF_LOOKAHEAD) - 1); \
220   if (nb > HUFF_LOOKAHEAD) { \
221     /* Equivalent of jpeg_huff_decode() */ \
222     /* Don't use GET_BITS() here because we don't want to modify bits_left */ \
223     s = (get_buffer >> bits_left) & ((1 << (nb)) - 1); \
224     while (s > htbl->maxcode[nb]) { \
225       s <<= 1; \
226       s |= GET_BITS(1); \
227       nb++; \
228     } \
229     s = htbl->pub->huffval[ (int) (s + htbl->valoffset[nb]) & 0xFF ]; \
230   }
231 
232 /* Out-of-line case for Huffman code fetching */
233 EXTERN(int) jpeg_huff_decode
234 	JPP((bitread_working_state * state, register bit_buf_type get_buffer,
235 	     register int bits_left, d_derived_tbl * htbl, int min_bits));
236