--- /dev/null
+/*
+ * jdhuff.h
+ *
+ * Copyright (C) 1991-1997, Thomas G. Lane.
+ * This file is part of the Independent JPEG Group's software.
+ * For conditions of distribution and use, see the accompanying README 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.
+ */
+
+/* Short forms of external names for systems with brain-damaged linkers. */
+
+#ifdef NEED_SHORT_EXTERNAL_NAMES
+#define jpeg_make_d_derived_tbl jMkDDerived
+#define jpeg_fill_bit_buffer jFilBitBuf
+#define jpeg_huff_decode jHufDecode
+#endif /* NEED_SHORT_EXTERNAL_NAMES */
+
+
+/* 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) */
+ INT32 maxcode[18]; /* largest code of length k (-1 if none) */
+ /* (maxcode[17] is a sentinel to ensure jpeg_huff_decode terminates) */
+ INT32 valoffset[17]; /* 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 tables: 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 these tables.
+ */
+ int look_nbits[1<<HUFF_LOOKAHEAD]; /* # bits, or 0 if too long */
+ UINT8 look_sym[1<<HUFF_LOOKAHEAD]; /* symbol, or unused */
+} d_derived_tbl;
+
+/* Expand a Huffman table definition into the derived format */
+EXTERN(void) jpeg_make_d_derived_tbl
+ JPP((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.
+ */
+
+typedef INT32 bit_buf_type; /* type of bit-extraction buffer */
+#define BIT_BUF_SIZE 32 /* size of buffer in bits */
+
+/* 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
+ JPP((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->look_nbits[look]) != 0) { \
+ DROP_BITS(nb); \
+ result = htbl->look_sym[look]; \
+ } else { \
+ nb = HUFF_LOOKAHEAD+1; \
+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; \
+ } \
+}
+
+/* Out-of-line case for Huffman code fetching */
+EXTERN(int) jpeg_huff_decode
+ JPP((bitread_working_state * state, register bit_buf_type get_buffer,
+ register int bits_left, d_derived_tbl * htbl, int min_bits));
projects / opencv / blobdiff