| /* |
| * jdhuff.c |
| * |
| * Copyright (C) 1991-1994, 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 Huffman entropy decoding routines. |
| * |
| * Much of the complexity here has to do with supporting input suspension. |
| * If the data source module demands suspension, we want to be able to back |
| * up to the start of the current MCU. To do this, we copy state variables |
| * into local working storage, and update them back to the permanent JPEG |
| * objects only upon successful completion of an MCU. |
| */ |
| |
| #define JPEG_INTERNALS |
| #include "jinclude.h" |
| #include "jpeglib.h" |
| |
| |
| /* 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 mincode[17]; /* smallest code of length k */ |
| INT32 maxcode[18]; /* largest code of length k (-1 if none) */ |
| /* (maxcode[17] is a sentinel to ensure huff_DECODE terminates) */ |
| int valptr[17]; /* huffval[] index of 1st symbol of length k */ |
| |
| /* Back link to public Huffman table (needed only in slow_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; |
| |
| /* Expanded entropy decoder object for Huffman decoding. |
| * |
| * The savable_state subrecord contains fields that change within an MCU, |
| * but must not be updated permanently until we complete the MCU. |
| */ |
| |
| typedef struct { |
| INT32 get_buffer; /* current bit-extraction buffer */ |
| int bits_left; /* # of unused bits in it */ |
| int last_dc_val[MAX_COMPS_IN_SCAN]; /* last DC coef for each component */ |
| } savable_state; |
| |
| /* This macro is to work around compilers with missing or broken |
| * structure assignment. You'll need to fix this code if you have |
| * such a compiler and you change MAX_COMPS_IN_SCAN. |
| */ |
| |
| #ifndef NO_STRUCT_ASSIGN |
| #define ASSIGN_STATE(dest,src) ((dest) = (src)) |
| #else |
| #if MAX_COMPS_IN_SCAN == 4 |
| #define ASSIGN_STATE(dest,src) \ |
| ((dest).get_buffer = (src).get_buffer, \ |
| (dest).bits_left = (src).bits_left, \ |
| (dest).last_dc_val[0] = (src).last_dc_val[0], \ |
| (dest).last_dc_val[1] = (src).last_dc_val[1], \ |
| (dest).last_dc_val[2] = (src).last_dc_val[2], \ |
| (dest).last_dc_val[3] = (src).last_dc_val[3]) |
| #endif |
| #endif |
| |
| |
| typedef struct { |
| struct jpeg_entropy_decoder pub; /* public fields */ |
| |
| savable_state saved; /* Bit buffer & DC state at start of MCU */ |
| |
| /* These fields are NOT loaded into local working state. */ |
| unsigned int restarts_to_go; /* MCUs left in this restart interval */ |
| boolean printed_eod; /* flag to suppress extra end-of-data msgs */ |
| |
| /* Pointers to derived tables (these workspaces have image lifespan) */ |
| D_DERIVED_TBL * dc_derived_tbls[NUM_HUFF_TBLS]; |
| D_DERIVED_TBL * ac_derived_tbls[NUM_HUFF_TBLS]; |
| } huff_entropy_decoder; |
| |
| typedef huff_entropy_decoder * huff_entropy_ptr; |
| |
| /* Working state while scanning an MCU. |
| * This struct contains all the fields that are needed by subroutines. |
| */ |
| |
| typedef struct { |
| int unread_marker; /* nonzero if we have hit a marker */ |
| const JOCTET * next_input_byte; /* => next byte to read from source */ |
| size_t bytes_in_buffer; /* # of bytes remaining in source buffer */ |
| savable_state cur; /* Current bit buffer & DC state */ |
| j_decompress_ptr cinfo; /* fill_bit_buffer needs access to this */ |
| } working_state; |
| |
| |
| /* Forward declarations */ |
| LOCAL void fix_huff_tbl JPP((j_decompress_ptr cinfo, JHUFF_TBL * htbl, |
| D_DERIVED_TBL ** pdtbl)); |
| |
| |
| /* |
| * Initialize for a Huffman-compressed scan. |
| */ |
| |
| METHODDEF void |
| start_pass_huff_decoder (j_decompress_ptr cinfo) |
| { |
| huff_entropy_ptr entropy = (huff_entropy_ptr) cinfo->entropy; |
| int ci, dctbl, actbl; |
| jpeg_component_info * compptr; |
| |
| for (ci = 0; ci < cinfo->comps_in_scan; ci++) { |
| compptr = cinfo->cur_comp_info[ci]; |
| dctbl = compptr->dc_tbl_no; |
| actbl = compptr->ac_tbl_no; |
| /* Make sure requested tables are present */ |
| if (dctbl < 0 || dctbl >= NUM_HUFF_TBLS || |
| cinfo->dc_huff_tbl_ptrs[dctbl] == NULL) |
| ERREXIT1(cinfo, JERR_NO_HUFF_TABLE, dctbl); |
| if (actbl < 0 || actbl >= NUM_HUFF_TBLS || |
| cinfo->ac_huff_tbl_ptrs[actbl] == NULL) |
| ERREXIT1(cinfo, JERR_NO_HUFF_TABLE, actbl); |
| /* Compute derived values for Huffman tables */ |
| /* We may do this more than once for a table, but it's not expensive */ |
| fix_huff_tbl(cinfo, cinfo->dc_huff_tbl_ptrs[dctbl], |
| & entropy->dc_derived_tbls[dctbl]); |
| fix_huff_tbl(cinfo, cinfo->ac_huff_tbl_ptrs[actbl], |
| & entropy->ac_derived_tbls[actbl]); |
| /* Initialize DC predictions to 0 */ |
| entropy->saved.last_dc_val[ci] = 0; |
| } |
| |
| /* Initialize private state variables */ |
| entropy->saved.bits_left = 0; |
| entropy->printed_eod = FALSE; |
| |
| /* Initialize restart counter */ |
| entropy->restarts_to_go = cinfo->restart_interval; |
| } |
| |
| |
| LOCAL void |
| fix_huff_tbl (j_decompress_ptr cinfo, JHUFF_TBL * htbl, D_DERIVED_TBL ** pdtbl) |
| /* Compute the derived values for a Huffman table */ |
| { |
| D_DERIVED_TBL *dtbl; |
| int p, i, l, si; |
| int lookbits, ctr; |
| char huffsize[257]; |
| unsigned int huffcode[257]; |
| unsigned int code; |
| |
| /* Allocate a workspace if we haven't already done so. */ |
| if (*pdtbl == NULL) |
| *pdtbl = (D_DERIVED_TBL *) |
| (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE, |
| SIZEOF(D_DERIVED_TBL)); |
| dtbl = *pdtbl; |
| dtbl->pub = htbl; /* fill in back link */ |
| |
| /* Figure C.1: make table of Huffman code length for each symbol */ |
| /* Note that this is in code-length order. */ |
| |
| p = 0; |
| for (l = 1; l <= 16; l++) { |
| for (i = 1; i <= (int) htbl->bits[l]; i++) |
| huffsize[p++] = (char) l; |
| } |
| huffsize[p] = 0; |
| |
| /* Figure C.2: generate the codes themselves */ |
| /* Note that this is in code-length order. */ |
| |
| code = 0; |
| si = huffsize[0]; |
| p = 0; |
| while (huffsize[p]) { |
| while (((int) huffsize[p]) == si) { |
| huffcode[p++] = code; |
| code++; |
| } |
| code <<= 1; |
| si++; |
| } |
| |
| /* Figure F.15: generate decoding tables for bit-sequential decoding */ |
| |
| p = 0; |
| for (l = 1; l <= 16; l++) { |
| if (htbl->bits[l]) { |
| dtbl->valptr[l] = p; /* huffval[] index of 1st symbol of code length l */ |
| dtbl->mincode[l] = huffcode[p]; /* minimum code of length l */ |
| p += htbl->bits[l]; |
| dtbl->maxcode[l] = huffcode[p-1]; /* maximum code of length l */ |
| } else { |
| dtbl->maxcode[l] = -1; /* -1 if no codes of this length */ |
| } |
| } |
| dtbl->maxcode[17] = 0xFFFFFL; /* ensures huff_DECODE terminates */ |
| |
| /* Compute lookahead tables to speed up decoding. |
| * First we set all the table entries to 0, indicating "too long"; |
| * then we iterate through the Huffman codes that are short enough and |
| * fill in all the entries that correspond to bit sequences starting |
| * with that code. |
| */ |
| |
| MEMZERO(dtbl->look_nbits, SIZEOF(dtbl->look_nbits)); |
| |
| p = 0; |
| for (l = 1; l <= HUFF_LOOKAHEAD; l++) { |
| for (i = 1; i <= (int) htbl->bits[l]; i++, p++) { |
| /* l = current code's length, p = its index in huffcode[] & huffval[]. */ |
| /* Generate left-justified code followed by all possible bit sequences */ |
| lookbits = huffcode[p] << (HUFF_LOOKAHEAD-l); |
| for (ctr = 1 << (HUFF_LOOKAHEAD-l); ctr > 0; ctr--) { |
| dtbl->look_nbits[lookbits] = l; |
| dtbl->look_sym[lookbits] = htbl->huffval[p]; |
| lookbits++; |
| } |
| } |
| } |
| } |
| |
| |
| /* |
| * Code for extracting the next N bits from the input stream. |
| * (N never exceeds 15 for JPEG data.) |
| * This needs to go as fast as possible! |
| * |
| * 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, fill_bit_buffer is called; it will attempt to fill get_buffer to |
| * the "high water mark" (not just to the number of bits needed; this reduces |
| * the function-call overhead cost of entering fill_bit_buffer). |
| * Note that fill_bit_buffer may return FALSE to indicate suspension. |
| * On TRUE return, fill_bit_buffer guarantees that get_buffer contains |
| * at least the requested number of bits --- dummy zeroes are inserted if |
| * necessary. |
| * |
| * On most machines MIN_GET_BITS should be 25 to allow the full 32-bit width |
| * of get_buffer to be used. (On machines with wider words, an even larger |
| * buffer could be used.) However, on some machines 32-bit shifts are |
| * quite slow and take time proportional to the number of places shifted. |
| * (This is true with most PC compilers, for instance.) In this case it may |
| * be a win to set MIN_GET_BITS to the minimum value of 15. This reduces the |
| * average shift distance at the cost of more calls to fill_bit_buffer. |
| */ |
| |
| #ifdef SLOW_SHIFT_32 |
| #define MIN_GET_BITS 15 /* minimum allowable value */ |
| #else |
| #define MIN_GET_BITS 25 /* max value for 32-bit get_buffer */ |
| #endif |
| |
| |
| LOCAL boolean |
| fill_bit_buffer (working_state * state, int nbits) |
| /* Load up the bit buffer to a depth of at least nbits */ |
| { |
| /* Copy heavily used state fields into locals (hopefully registers) */ |
| register const JOCTET * next_input_byte = state->next_input_byte; |
| register size_t bytes_in_buffer = state->bytes_in_buffer; |
| register INT32 get_buffer = state->cur.get_buffer; |
| register int bits_left = state->cur.bits_left; |
| register int c; |
| |
| /* Attempt to load at least MIN_GET_BITS bits into get_buffer. */ |
| /* (It is assumed that no request will be for more than that many bits.) */ |
| |
| while (bits_left < MIN_GET_BITS) { |
| /* Attempt to read a byte */ |
| if (state->unread_marker != 0) |
| goto no_more_data; /* can't advance past a marker */ |
| |
| if (bytes_in_buffer == 0) { |
| if (! (*state->cinfo->src->fill_input_buffer) (state->cinfo)) |
| return FALSE; |
| next_input_byte = state->cinfo->src->next_input_byte; |
| bytes_in_buffer = state->cinfo->src->bytes_in_buffer; |
| } |
| bytes_in_buffer--; |
| c = GETJOCTET(*next_input_byte++); |
| |
| /* If it's 0xFF, check and discard stuffed zero byte */ |
| if (c == 0xFF) { |
| do { |
| if (bytes_in_buffer == 0) { |
| if (! (*state->cinfo->src->fill_input_buffer) (state->cinfo)) |
| return FALSE; |
| next_input_byte = state->cinfo->src->next_input_byte; |
| bytes_in_buffer = state->cinfo->src->bytes_in_buffer; |
| } |
| bytes_in_buffer--; |
| c = GETJOCTET(*next_input_byte++); |
| } while (c == 0xFF); |
| |
| if (c == 0) { |
| /* Found FF/00, which represents an FF data byte */ |
| c = 0xFF; |
| } else { |
| /* Oops, it's actually a marker indicating end of compressed data. */ |
| /* Better put it back for use later */ |
| state->unread_marker = c; |
| |
| no_more_data: |
| /* There should be enough bits still left in the data segment; */ |
| /* if so, just break out of the outer while loop. */ |
| if (bits_left >= nbits) |
| break; |
| /* Uh-oh. Report corrupted data to user and stuff zeroes into |
| * the data stream, so that we can produce some kind of image. |
| * Note that this will be repeated for each byte demanded for the |
| * rest of the segment; this is slow but not unreasonably so. |
| * The main thing is to avoid getting a zillion warnings, hence |
| * we use a flag to ensure that only one warning appears. |
| */ |
| if (! ((huff_entropy_ptr) state->cinfo->entropy)->printed_eod) { |
| WARNMS(state->cinfo, JWRN_HIT_MARKER); |
| ((huff_entropy_ptr) state->cinfo->entropy)->printed_eod = TRUE; |
| } |
| c = 0; /* insert a zero byte into bit buffer */ |
| } |
| } |
| |
| /* OK, load c into get_buffer */ |
| get_buffer = (get_buffer << 8) | c; |
| bits_left += 8; |
| } |
| |
| /* Unload the local registers */ |
| state->next_input_byte = next_input_byte; |
| state->bytes_in_buffer = bytes_in_buffer; |
| state->cur.get_buffer = get_buffer; |
| state->cur.bits_left = bits_left; |
| |
| return TRUE; |
| } |
| |
| |
| /* |
| * 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. |
| * check_bit_buffer(state,n,action); |
| * Ensure there are N bits in get_buffer; if suspend, take action. |
| * val = get_bits(state,n); |
| * Fetch next N bits. |
| * val = peek_bits(state,n); |
| * Fetch next N bits without removing them from the buffer. |
| * drop_bits(state,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 ((state).cur.bits_left < (nbits)) \ |
| if (! fill_bit_buffer(&(state), nbits)) \ |
| { action; } } |
| |
| #define get_bits(state,nbits) \ |
| (((int) ((state).cur.get_buffer >> ((state).cur.bits_left -= (nbits)))) & ((1<<(nbits))-1)) |
| |
| #define peek_bits(state,nbits) \ |
| (((int) ((state).cur.get_buffer >> ((state).cur.bits_left - (nbits)))) & ((1<<(nbits))-1)) |
| |
| #define drop_bits(state,nbits) \ |
| ((state).cur.bits_left -= (nbits)) |
| |
| |
| /* |
| * Code for extracting next Huffman-coded symbol from input bit stream. |
| * 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. |
| * The primary case is made a macro for speed reasons; the secondary |
| * routine slow_DECODE is rarely entered and 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. slow_DECODE returns -1 if forced to suspend. |
| */ |
| |
| #define huff_DECODE(result,state,htbl,donelabel) \ |
| { if (state.cur.bits_left < HUFF_LOOKAHEAD) { \ |
| if (! fill_bit_buffer(&state, 0)) return FALSE; \ |
| if (state.cur.bits_left < HUFF_LOOKAHEAD) { \ |
| if ((result = slow_DECODE(&state, htbl, 1)) < 0) return FALSE; \ |
| goto donelabel; \ |
| } \ |
| } \ |
| { register int nb, look; \ |
| look = peek_bits(state, HUFF_LOOKAHEAD); \ |
| if ((nb = htbl->look_nbits[look]) != 0) { \ |
| drop_bits(state, nb); \ |
| result = htbl->look_sym[look]; \ |
| } else { \ |
| if ((result = slow_DECODE(&state, htbl, HUFF_LOOKAHEAD+1)) < 0) \ |
| return FALSE; \ |
| } \ |
| } \ |
| donelabel:; \ |
| } |
| |
| |
| LOCAL int |
| slow_DECODE (working_state * state, D_DERIVED_TBL * htbl, int min_bits) |
| { |
| register int l = min_bits; |
| register INT32 code; |
| |
| /* huff_DECODE has determined that the code is at least min_bits */ |
| /* bits long, so fetch that many bits in one swoop. */ |
| |
| check_bit_buffer(*state, l, return -1); |
| code = get_bits(*state, l); |
| |
| /* Collect the rest of the Huffman code one bit at a time. */ |
| /* This is per Figure F.16 in the JPEG spec. */ |
| |
| while (code > htbl->maxcode[l]) { |
| code <<= 1; |
| check_bit_buffer(*state, 1, return -1); |
| code |= get_bits(*state, 1); |
| l++; |
| } |
| |
| /* With garbage input we may reach the sentinel value l = 17. */ |
| |
| if (l > 16) { |
| WARNMS(state->cinfo, JWRN_HUFF_BAD_CODE); |
| return 0; /* fake a zero as the safest result */ |
| } |
| |
| return htbl->pub->huffval[ htbl->valptr[l] + |
| ((int) (code - htbl->mincode[l])) ]; |
| } |
| |
| |
| /* Figure F.12: extend sign bit. |
| * On some machines, a shift and add will be faster than a table lookup. |
| */ |
| |
| #ifdef AVOID_TABLES |
| |
| #define huff_EXTEND(x,s) ((x) < (1<<((s)-1)) ? (x) + (((-1)<<(s)) + 1) : (x)) |
| |
| #else |
| |
| #define huff_EXTEND(x,s) ((x) < extend_test[s] ? (x) + extend_offset[s] : (x)) |
| |
| static const int extend_test[16] = /* entry n is 2**(n-1) */ |
| { 0, 0x0001, 0x0002, 0x0004, 0x0008, 0x0010, 0x0020, 0x0040, 0x0080, |
| 0x0100, 0x0200, 0x0400, 0x0800, 0x1000, 0x2000, 0x4000 }; |
| |
| static const int extend_offset[16] = /* entry n is (-1 << n) + 1 */ |
| { 0, ((-1)<<1) + 1, ((-1)<<2) + 1, ((-1)<<3) + 1, ((-1)<<4) + 1, |
| ((-1)<<5) + 1, ((-1)<<6) + 1, ((-1)<<7) + 1, ((-1)<<8) + 1, |
| ((-1)<<9) + 1, ((-1)<<10) + 1, ((-1)<<11) + 1, ((-1)<<12) + 1, |
| ((-1)<<13) + 1, ((-1)<<14) + 1, ((-1)<<15) + 1 }; |
| |
| #endif /* AVOID_TABLES */ |
| |
| |
| /* |
| * Check for a restart marker & resynchronize decoder. |
| * Returns FALSE if must suspend. |
| */ |
| |
| LOCAL boolean |
| process_restart (j_decompress_ptr cinfo) |
| { |
| huff_entropy_ptr entropy = (huff_entropy_ptr) cinfo->entropy; |
| int ci; |
| |
| /* Throw away any unused bits remaining in bit buffer; */ |
| /* include any full bytes in next_marker's count of discarded bytes */ |
| cinfo->marker->discarded_bytes += entropy->saved.bits_left / 8; |
| entropy->saved.bits_left = 0; |
| |
| /* Advance past the RSTn marker */ |
| if (! (*cinfo->marker->read_restart_marker) (cinfo)) |
| return FALSE; |
| |
| /* Re-initialize DC predictions to 0 */ |
| for (ci = 0; ci < cinfo->comps_in_scan; ci++) |
| entropy->saved.last_dc_val[ci] = 0; |
| |
| /* Reset restart counter */ |
| entropy->restarts_to_go = cinfo->restart_interval; |
| |
| entropy->printed_eod = FALSE; /* next segment can get another warning */ |
| |
| return TRUE; |
| } |
| |
| |
| /* ZAG[i] is the natural-order position of the i'th element of zigzag order. |
| * If the incoming data is corrupted, decode_mcu could attempt to |
| * reference values beyond the end of the array. To avoid a wild store, |
| * we put some extra zeroes after the real entries. |
| */ |
| |
| static const int ZAG[DCTSIZE2+16] = { |
| 0, 1, 8, 16, 9, 2, 3, 10, |
| 17, 24, 32, 25, 18, 11, 4, 5, |
| 12, 19, 26, 33, 40, 48, 41, 34, |
| 27, 20, 13, 6, 7, 14, 21, 28, |
| 35, 42, 49, 56, 57, 50, 43, 36, |
| 29, 22, 15, 23, 30, 37, 44, 51, |
| 58, 59, 52, 45, 38, 31, 39, 46, |
| 53, 60, 61, 54, 47, 55, 62, 63, |
| 0, 0, 0, 0, 0, 0, 0, 0, /* extra entries in case k>63 below */ |
| 0, 0, 0, 0, 0, 0, 0, 0 |
| }; |
| |
| |
| /* |
| * Decode and return one MCU's worth of Huffman-compressed coefficients. |
| * The coefficients are reordered from zigzag order into natural array order, |
| * but are not dequantized. |
| * |
| * The i'th block of the MCU is stored into the block pointed to by |
| * MCU_data[i]. WE ASSUME THIS AREA HAS BEEN ZEROED BY THE CALLER. |
| * (Wholesale zeroing is usually a little faster than retail...) |
| * |
| * Returns FALSE if data source requested suspension. In that case no |
| * changes have been made to permanent state. (Exception: some output |
| * coefficients may already have been assigned. This is harmless for |
| * this module, but would not work for decoding progressive JPEG.) |
| */ |
| |
| METHODDEF boolean |
| decode_mcu (j_decompress_ptr cinfo, JBLOCKROW *MCU_data) |
| { |
| huff_entropy_ptr entropy = (huff_entropy_ptr) cinfo->entropy; |
| register int s, k, r; |
| int blkn, ci; |
| JBLOCKROW block; |
| working_state state; |
| D_DERIVED_TBL * dctbl; |
| D_DERIVED_TBL * actbl; |
| jpeg_component_info * compptr; |
| |
| /* Process restart marker if needed; may have to suspend */ |
| if (cinfo->restart_interval) { |
| if (entropy->restarts_to_go == 0) |
| if (! process_restart(cinfo)) |
| return FALSE; |
| } |
| |
| /* Load up working state */ |
| state.unread_marker = cinfo->unread_marker; |
| state.next_input_byte = cinfo->src->next_input_byte; |
| state.bytes_in_buffer = cinfo->src->bytes_in_buffer; |
| ASSIGN_STATE(state.cur, entropy->saved); |
| state.cinfo = cinfo; |
| |
| /* Outer loop handles each block in the MCU */ |
| |
| for (blkn = 0; blkn < cinfo->blocks_in_MCU; blkn++) { |
| block = MCU_data[blkn]; |
| ci = cinfo->MCU_membership[blkn]; |
| compptr = cinfo->cur_comp_info[ci]; |
| dctbl = entropy->dc_derived_tbls[compptr->dc_tbl_no]; |
| actbl = entropy->ac_derived_tbls[compptr->ac_tbl_no]; |
| |
| /* Decode a single block's worth of coefficients */ |
| |
| /* Section F.2.2.1: decode the DC coefficient difference */ |
| huff_DECODE(s, state, dctbl, label1); |
| if (s) { |
| check_bit_buffer(state, s, return FALSE); |
| r = get_bits(state, s); |
| s = huff_EXTEND(r, s); |
| } |
| |
| /* Shortcut if component's values are not interesting */ |
| if (! compptr->component_needed) |
| goto skip_ACs; |
| |
| /* Convert DC difference to actual value, update last_dc_val */ |
| s += state.cur.last_dc_val[ci]; |
| state.cur.last_dc_val[ci] = s; |
| /* Output the DC coefficient (assumes ZAG[0] = 0) */ |
| (*block)[0] = (JCOEF) s; |
| |
| /* Do we need to decode the AC coefficients for this component? */ |
| if (compptr->DCT_scaled_size > 1) { |
| |
| /* Section F.2.2.2: decode the AC coefficients */ |
| /* Since zeroes are skipped, output area must be cleared beforehand */ |
| for (k = 1; k < DCTSIZE2; k++) { |
| huff_DECODE(s, state, actbl, label2); |
| |
| r = s >> 4; |
| s &= 15; |
| |
| if (s) { |
| k += r; |
| check_bit_buffer(state, s, return FALSE); |
| r = get_bits(state, s); |
| s = huff_EXTEND(r, s); |
| /* Output coefficient in natural (dezigzagged) order */ |
| (*block)[ZAG[k]] = (JCOEF) s; |
| } else { |
| if (r != 15) |
| break; |
| k += 15; |
| } |
| } |
| |
| } else { |
| skip_ACs: |
| |
| /* Section F.2.2.2: decode the AC coefficients */ |
| /* In this path we just discard the values */ |
| for (k = 1; k < DCTSIZE2; k++) { |
| huff_DECODE(s, state, actbl, label3); |
| |
| r = s >> 4; |
| s &= 15; |
| |
| if (s) { |
| k += r; |
| check_bit_buffer(state, s, return FALSE); |
| drop_bits(state, s); |
| } else { |
| if (r != 15) |
| break; |
| k += 15; |
| } |
| } |
| |
| } |
| } |
| |
| /* Completed MCU, so update state */ |
| cinfo->unread_marker = state.unread_marker; |
| cinfo->src->next_input_byte = state.next_input_byte; |
| cinfo->src->bytes_in_buffer = state.bytes_in_buffer; |
| ASSIGN_STATE(entropy->saved, state.cur); |
| |
| /* Account for restart interval (no-op if not using restarts) */ |
| entropy->restarts_to_go--; |
| |
| return TRUE; |
| } |
| |
| |
| /* |
| * Module initialization routine for Huffman entropy decoding. |
| */ |
| |
| GLOBAL void |
| jinit_huff_decoder (j_decompress_ptr cinfo) |
| { |
| huff_entropy_ptr entropy; |
| int i; |
| |
| entropy = (huff_entropy_ptr) |
| (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE, |
| SIZEOF(huff_entropy_decoder)); |
| cinfo->entropy = (struct jpeg_entropy_decoder *) entropy; |
| entropy->pub.start_pass = start_pass_huff_decoder; |
| entropy->pub.decode_mcu = decode_mcu; |
| |
| /* Mark tables unallocated */ |
| for (i = 0; i < NUM_HUFF_TBLS; i++) { |
| entropy->dc_derived_tbls[i] = entropy->ac_derived_tbls[i] = NULL; |
| } |
| } |