4 * This file was part of the Independent JPEG Group's software:
5 * Copyright (C) 1991-1997, Thomas G. Lane.
6 * Lossless JPEG Modifications:
7 * Copyright (C) 1999, Ken Murchison.
8 * libjpeg-turbo Modifications:
9 * Copyright (C) 2022, D. R. Commander.
10 * For conditions of distribution and use, see the accompanying README.ijg
13 * This file contains Huffman entropy decoding routines for lossless JPEG.
15 * Much of the complexity here has to do with supporting input suspension.
16 * If the data source module demands suspension, we want to be able to back
17 * up to the start of the current MCU. To do this, we copy state variables
18 * into local working storage, and update them back to the permanent
19 * storage only upon successful completion of an MCU.
22 #define JPEG_INTERNALS
25 #include "jlossls.h" /* Private declarations for lossless codec */
26 #include "jdhuff.h" /* Declarations shared with jd*huff.c */
29 #ifdef D_LOSSLESS_SUPPORTED
32 int ci, yoffset, MCU_width;
33 } lhd_output_ptr_info;
36 * Expanded entropy decoder object for Huffman decoding in lossless mode.
40 struct jpeg_entropy_decoder pub; /* public fields */
42 /* These fields are loaded into local variables at start of each MCU.
43 * In case of suspension, we exit WITHOUT updating them.
45 bitread_perm_state bitstate; /* Bit buffer at start of MCU */
47 /* Pointers to derived tables (these workspaces have image lifespan) */
48 d_derived_tbl *derived_tbls[NUM_HUFF_TBLS];
50 /* Precalculated info set up by start_pass for use in decode_mcus: */
52 /* Pointers to derived tables to be used for each data unit within an MCU */
53 d_derived_tbl *cur_tbls[D_MAX_BLOCKS_IN_MCU];
55 /* Pointers to the proper output difference row for each group of data units
56 * within an MCU. For each component, there are Vi groups of Hi data units.
58 JDIFFROW output_ptr[D_MAX_BLOCKS_IN_MCU];
60 /* Number of output pointers in use for the current MCU. This is the sum
61 * of all Vi in the MCU.
65 /* Information used for positioning the output pointers within the output
68 lhd_output_ptr_info output_ptr_info[D_MAX_BLOCKS_IN_MCU];
70 /* Index of the proper output pointer for each data unit within an MCU */
71 int output_ptr_index[D_MAX_BLOCKS_IN_MCU];
73 } lhuff_entropy_decoder;
75 typedef lhuff_entropy_decoder *lhuff_entropy_ptr;
79 * Initialize for a Huffman-compressed scan.
83 start_pass_lhuff_decoder(j_decompress_ptr cinfo)
85 lhuff_entropy_ptr entropy = (lhuff_entropy_ptr)cinfo->entropy;
86 int ci, dctbl, sampn, ptrn, yoffset, xoffset;
87 jpeg_component_info *compptr;
89 for (ci = 0; ci < cinfo->comps_in_scan; ci++) {
90 compptr = cinfo->cur_comp_info[ci];
91 dctbl = compptr->dc_tbl_no;
92 /* Make sure requested tables are present */
93 if (dctbl < 0 || dctbl >= NUM_HUFF_TBLS ||
94 cinfo->dc_huff_tbl_ptrs[dctbl] == NULL)
95 ERREXIT1(cinfo, JERR_NO_HUFF_TABLE, dctbl);
96 /* Compute derived values for Huffman tables */
97 /* We may do this more than once for a table, but it's not expensive */
98 jpeg_make_d_derived_tbl(cinfo, TRUE, dctbl,
99 &entropy->derived_tbls[dctbl]);
102 /* Precalculate decoding info for each sample in an MCU of this scan */
103 for (sampn = 0, ptrn = 0; sampn < cinfo->blocks_in_MCU;) {
104 compptr = cinfo->cur_comp_info[cinfo->MCU_membership[sampn]];
105 ci = compptr->component_index;
106 for (yoffset = 0; yoffset < compptr->MCU_height; yoffset++, ptrn++) {
107 /* Precalculate the setup info for each output pointer */
108 entropy->output_ptr_info[ptrn].ci = ci;
109 entropy->output_ptr_info[ptrn].yoffset = yoffset;
110 entropy->output_ptr_info[ptrn].MCU_width = compptr->MCU_width;
111 for (xoffset = 0; xoffset < compptr->MCU_width; xoffset++, sampn++) {
112 /* Precalculate the output pointer index for each sample */
113 entropy->output_ptr_index[sampn] = ptrn;
114 /* Precalculate which table to use for each sample */
115 entropy->cur_tbls[sampn] = entropy->derived_tbls[compptr->dc_tbl_no];
119 entropy->num_output_ptrs = ptrn;
121 /* Initialize bitread state variables */
122 entropy->bitstate.bits_left = 0;
123 entropy->bitstate.get_buffer = 0; /* unnecessary, but keeps Purify quiet */
124 entropy->pub.insufficient_data = FALSE;
129 * Figure F.12: extend sign bit.
130 * On some machines, a shift and add will be faster than a table lookup.
136 #define NEG_1 ((unsigned int)-1)
137 #define HUFF_EXTEND(x, s) \
138 ((x) + ((((x) - (1 << ((s) - 1))) >> 31) & (((NEG_1) << (s)) + 1)))
142 #define HUFF_EXTEND(x, s) \
143 ((x) < extend_test[s] ? (x) + extend_offset[s] : (x))
145 static const int extend_test[16] = { /* entry n is 2**(n-1) */
146 0, 0x0001, 0x0002, 0x0004, 0x0008, 0x0010, 0x0020, 0x0040, 0x0080,
147 0x0100, 0x0200, 0x0400, 0x0800, 0x1000, 0x2000, 0x4000
150 static const int extend_offset[16] = { /* entry n is (-1 << n) + 1 */
151 0, ((-1) << 1) + 1, ((-1) << 2) + 1, ((-1) << 3) + 1, ((-1) << 4) + 1,
152 ((-1) << 5) + 1, ((-1) << 6) + 1, ((-1) << 7) + 1, ((-1) << 8) + 1,
153 ((-1) << 9) + 1, ((-1) << 10) + 1, ((-1) << 11) + 1, ((-1) << 12) + 1,
154 ((-1) << 13) + 1, ((-1) << 14) + 1, ((-1) << 15) + 1
157 #endif /* AVOID_TABLES */
161 * Check for a restart marker & resynchronize decoder.
162 * Returns FALSE if must suspend.
166 process_restart(j_decompress_ptr cinfo)
168 lhuff_entropy_ptr entropy = (lhuff_entropy_ptr)cinfo->entropy;
170 /* Throw away any unused bits remaining in bit buffer; */
171 /* include any full bytes in next_marker's count of discarded bytes */
172 cinfo->marker->discarded_bytes += entropy->bitstate.bits_left / 8;
173 entropy->bitstate.bits_left = 0;
175 /* Advance past the RSTn marker */
176 if (!(*cinfo->marker->read_restart_marker) (cinfo))
179 /* Reset out-of-data flag, unless read_restart_marker left us smack up
180 * against a marker. In that case we will end up treating the next data
181 * segment as empty, and we can avoid producing bogus output pixels by
182 * leaving the flag set.
184 if (cinfo->unread_marker == 0)
185 entropy->pub.insufficient_data = FALSE;
192 * Decode and return nMCU MCUs' worth of Huffman-compressed differences.
193 * Each MCU is also disassembled and placed accordingly in diff_buf.
195 * MCU_col_num specifies the column of the first MCU being requested within
196 * the MCU row. This tells us where to position the output row pointers in
199 * Returns the number of MCUs decoded. This may be less than nMCU MCUs if
200 * data source requested suspension. In that case no changes have been made
201 * to permanent state. (Exception: some output differences may already have
202 * been assigned. This is harmless for this module, since we'll just
203 * re-assign them on the next call.)
206 METHODDEF(JDIMENSION)
207 decode_mcus(j_decompress_ptr cinfo, JDIFFIMAGE diff_buf,
208 JDIMENSION MCU_row_num, JDIMENSION MCU_col_num, JDIMENSION nMCU)
210 lhuff_entropy_ptr entropy = (lhuff_entropy_ptr)cinfo->entropy;
211 int sampn, ci, yoffset, MCU_width, ptrn;
215 /* Set output pointer locations based on MCU_col_num */
216 for (ptrn = 0; ptrn < entropy->num_output_ptrs; ptrn++) {
217 ci = entropy->output_ptr_info[ptrn].ci;
218 yoffset = entropy->output_ptr_info[ptrn].yoffset;
219 MCU_width = entropy->output_ptr_info[ptrn].MCU_width;
220 entropy->output_ptr[ptrn] =
221 diff_buf[ci][MCU_row_num + yoffset] + (MCU_col_num * MCU_width);
225 * If we've run out of data, zero out the buffers and return.
226 * By resetting the undifferencer, the output samples will be CENTERJSAMPLE.
228 * NB: We should find a way to do this without interacting with the
229 * undifferencer module directly.
231 if (entropy->pub.insufficient_data) {
232 for (ptrn = 0; ptrn < entropy->num_output_ptrs; ptrn++)
233 jzero_far((void FAR *)entropy->output_ptr[ptrn],
234 nMCU * entropy->output_ptr_info[ptrn].MCU_width *
237 (*cinfo->idct->start_pass) (cinfo);
241 /* Load up working state */
242 BITREAD_LOAD_STATE(cinfo, entropy->bitstate);
244 /* Outer loop handles the number of MCUs requested */
246 for (mcu_num = 0; mcu_num < nMCU; mcu_num++) {
248 /* Inner loop handles the samples in the MCU */
249 for (sampn = 0; sampn < cinfo->blocks_in_MCU; sampn++) {
250 d_derived_tbl *dctbl = entropy->cur_tbls[sampn];
253 /* Section H.2.2: decode the sample difference */
254 HUFF_DECODE(s, br_state, dctbl, return mcu_num, label1);
256 if (s == 16) /* special case: always output 32768 */
258 else { /* normal case: fetch subsequent bits */
259 CHECK_BIT_BUFFER(br_state, s, return mcu_num);
261 s = HUFF_EXTEND(r, s);
265 /* Output the sample difference */
266 *entropy->output_ptr[entropy->output_ptr_index[sampn]]++ = (JDIFF)s;
269 /* Completed MCU, so update state */
270 BITREAD_SAVE_STATE(cinfo, entropy->bitstate);
279 * Module initialization routine for lossless mode Huffman entropy decoding.
283 jinit_lhuff_decoder(j_decompress_ptr cinfo)
285 lhuff_entropy_ptr entropy;
288 entropy = (lhuff_entropy_ptr)
289 (*cinfo->mem->alloc_small) ((j_common_ptr)cinfo, JPOOL_IMAGE,
290 sizeof(lhuff_entropy_decoder));
291 cinfo->entropy = (struct jpeg_entropy_decoder *)entropy;
292 entropy->pub.start_pass = start_pass_lhuff_decoder;
293 entropy->pub.decode_mcus = decode_mcus;
294 entropy->pub.process_restart = process_restart;
296 /* Mark tables unallocated */
297 for (i = 0; i < NUM_HUFF_TBLS; i++) {
298 entropy->derived_tbls[i] = NULL;
302 #endif /* D_LOSSLESS_SUPPORTED */