550 lines
17 KiB
C++
550 lines
17 KiB
C++
// * jdhuff.c
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// *
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// * Copyright (C) 1991-1995, Thomas G. Lane.
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// * This file is part of the Independent JPEG Group's software.
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// * For conditions of distribution and use, see the accompanying README file.
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// *
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// * This file contains Huffman entropy decoding routines.
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// *
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// * Much of the complexity here has to do with supporting input suspension.
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// * If the data source module demands suspension, we want to be able to back
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// * up to the start of the current MCU. To do this, we copy state variables
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// * into local working storage, and update them back to the permanent
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// * storage only upon successful completion of an MCU.
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#define JPEG_INTERNALS
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#include "JINCLUDE.h"
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#include "JPEGLIB.h"
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#include "JDHUFF.h" // Declarations shared with jdphuff.c
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// * Expanded entropy decoder object for Huffman decoding.
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// *
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// * The savable_state subrecord contains fields that change within an MCU,
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// * but must not be updated permanently until we complete the MCU.
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typedef struct {
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int last_dc_val[MAX_COMPS_IN_SCAN]; // last DC coef for each component
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} savable_state;
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// This macro is to work around compilers with missing or broken
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// * structure assignment. You'll need to fix this code if you have
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// * such a compiler and you change MAX_COMPS_IN_SCAN.
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#ifndef NO_STRUCT_ASSIGN
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#define ASSIGN_STATE(dest,src) ((dest) = (src))
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#else
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#if MAX_COMPS_IN_SCAN == 4
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#define ASSIGN_STATE(dest,src) \
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((dest).last_dc_val[0] = (src).last_dc_val[0], \
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(dest).last_dc_val[1] = (src).last_dc_val[1], \
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(dest).last_dc_val[2] = (src).last_dc_val[2], \
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(dest).last_dc_val[3] = (src).last_dc_val[3])
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#endif
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#endif
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typedef struct {
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struct jpeg_entropy_decoder pub; // public fields
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// These fields are loaded into local variables at start of each MCU.
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// * In case of suspension, we exit WITHOUT updating them.
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bitread_perm_state bitstate; // Bit buffer at start of MCU
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savable_state saved; // Other state at start of MCU
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// These fields are NOT loaded into local working state.
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unsigned int restarts_to_go; // MCUs left in this restart interval
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// Pointers to derived tables (these workspaces have image lifespan)
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d_derived_tbl * dc_derived_tbls[NUM_HUFF_TBLS];
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d_derived_tbl * ac_derived_tbls[NUM_HUFF_TBLS];
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} huff_entropy_decoder;
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typedef huff_entropy_decoder * huff_entropy_ptr;
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// * Initialize for a Huffman-compressed scan.
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METHODDEF void
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start_pass_huff_decoder (j_decompress_ptr cinfo)
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{
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huff_entropy_ptr entropy = (huff_entropy_ptr) cinfo->entropy;
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int ci, dctbl, actbl;
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jpeg_component_info * compptr;
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// Check that the scan parameters Ss, Se, Ah/Al are OK for sequential JPEG.
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// * This ought to be an error condition, but we make it a warning because
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// * there are some baseline files out there with all zeroes in these bytes.
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if (cinfo->Ss != 0 || cinfo->Se != DCTSIZE2-1 ||
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cinfo->Ah != 0 || cinfo->Al != 0)
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WARNMS(cinfo, JWRN_NOT_SEQUENTIAL);
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for (ci = 0; ci < cinfo->comps_in_scan; ci++) {
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compptr = cinfo->cur_comp_info[ci];
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dctbl = compptr->dc_tbl_no;
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actbl = compptr->ac_tbl_no;
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// Make sure requested tables are present
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if (dctbl < 0 || dctbl >= NUM_HUFF_TBLS ||
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cinfo->dc_huff_tbl_ptrs[dctbl] == NULL)
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ERREXIT1(cinfo, JERR_NO_HUFF_TABLE, dctbl);
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if (actbl < 0 || actbl >= NUM_HUFF_TBLS ||
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cinfo->ac_huff_tbl_ptrs[actbl] == NULL)
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ERREXIT1(cinfo, JERR_NO_HUFF_TABLE, actbl);
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// Compute derived values for Huffman tables
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// We may do this more than once for a table, but it's not expensive
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jpeg_make_d_derived_tbl(cinfo, cinfo->dc_huff_tbl_ptrs[dctbl],
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& entropy->dc_derived_tbls[dctbl]);
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jpeg_make_d_derived_tbl(cinfo, cinfo->ac_huff_tbl_ptrs[actbl],
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& entropy->ac_derived_tbls[actbl]);
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// Initialize DC predictions to 0
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entropy->saved.last_dc_val[ci] = 0;
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}
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// Initialize bitread state variables
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entropy->bitstate.bits_left = 0;
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entropy->bitstate.get_buffer = 0; // unnecessary, but keeps Purify quiet
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entropy->bitstate.printed_eod = FALSE;
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// Initialize restart counter
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entropy->restarts_to_go = cinfo->restart_interval;
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}
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// * Compute the derived values for a Huffman table.
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// * Note this is also used by jdphuff.c.
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GLOBAL void
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jpeg_make_d_derived_tbl (j_decompress_ptr cinfo, JHUFF_TBL * htbl,
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d_derived_tbl ** pdtbl)
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{
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d_derived_tbl *dtbl;
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int p, i, l, si;
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int lookbits, ctr;
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char huffsize[257];
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unsigned int huffcode[257];
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unsigned int code;
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// Allocate a workspace if we haven't already done so.
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if (*pdtbl == NULL)
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*pdtbl = (d_derived_tbl *)
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(*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
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SIZEOF(d_derived_tbl));
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dtbl = *pdtbl;
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dtbl->pub = htbl; // fill in back link
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// Figure C.1: make table of Huffman code length for each symbol
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// Note that this is in code-length order.
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p = 0;
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for (l = 1; l <= 16; l++) {
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for (i = 1; i <= (int) htbl->bits[l]; i++)
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huffsize[p++] = (char) l;
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}
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huffsize[p] = 0;
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// Figure C.2: generate the codes themselves
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// Note that this is in code-length order.
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code = 0;
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si = huffsize[0];
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p = 0;
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while (huffsize[p]) {
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while (((int) huffsize[p]) == si) {
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huffcode[p++] = code;
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code++;
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}
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code <<= 1;
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si++;
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}
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// Figure F.15: generate decoding tables for bit-sequential decoding
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p = 0;
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for (l = 1; l <= 16; l++) {
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if (htbl->bits[l]) {
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dtbl->valptr[l] = p; // huffval[] index of 1st symbol of code length l
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dtbl->mincode[l] = huffcode[p]; // minimum code of length l
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p += htbl->bits[l];
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dtbl->maxcode[l] = huffcode[p-1]; // maximum code of length l
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} else {
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dtbl->maxcode[l] = -1; // -1 if no codes of this length
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}
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}
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dtbl->maxcode[17] = 0xFFFFFL; // ensures jpeg_huff_decode terminates
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// Compute lookahead tables to speed up decoding.
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// * First we set all the table entries to 0, indicating "too LONG";
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// * then we iterate through the Huffman codes that are short enough and
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// * fill in all the entries that correspond to bit sequences starting
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// * with that code.
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MEMZERO(dtbl->look_nbits, SIZEOF(dtbl->look_nbits));
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p = 0;
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for (l = 1; l <= HUFF_LOOKAHEAD; l++) {
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for (i = 1; i <= (int) htbl->bits[l]; i++, p++) {
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// l = current code's length, p = its index in huffcode[] & huffval[].
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// Generate left-justified code followed by all possible bit sequences
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lookbits = huffcode[p] << (HUFF_LOOKAHEAD-l);
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for (ctr = 1 << (HUFF_LOOKAHEAD-l); ctr > 0; ctr--) {
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dtbl->look_nbits[lookbits] = l;
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dtbl->look_sym[lookbits] = htbl->huffval[p];
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lookbits++;
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}
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}
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}
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}
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// * Out-of-line code for bit fetching (shared with jdphuff.c).
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// * See jdhuff.h for info about usage.
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// * Note: current values of get_buffer and bits_left are passed as parameters,
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// * but are returned in the corresponding fields of the state struct.
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// *
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// * On most machines MIN_GET_BITS should be 25 to allow the full 32-bit width
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// * of get_buffer to be used. (On machines with wider words, an even larger
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// * buffer could be used.) However, on some machines 32-bit shifts are
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// * quite slow and take time proportional to the number of places shifted.
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// * (This is true with most PC compilers, for instance.) In this case it may
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// * be a win to set MIN_GET_BITS to the minimum value of 15. This reduces the
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// * average shift distance at the cost of more calls to jpeg_fill_bit_buffer.
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#ifdef SLOW_SHIFT_32
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#define MIN_GET_BITS 15 // minimum allowable value
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#else
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#define MIN_GET_BITS (BIT_BUF_SIZE-7)
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#endif
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GLOBAL boolean
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jpeg_fill_bit_buffer (bitread_working_state * state,
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register bit_buf_type get_buffer, register int bits_left,
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int nbits)
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// Load up the bit buffer to a depth of at least nbits
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{
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// Copy heavily used state fields into locals (hopefully registers)
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register const JOCTET * next_input_byte = state->next_input_byte;
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register size_t bytes_in_buffer = state->bytes_in_buffer;
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register int c;
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// Attempt to load at least MIN_GET_BITS bits into get_buffer.
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// (It is assumed that no request will be for more than that many bits.)
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while (bits_left < MIN_GET_BITS) {
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// Attempt to read a byte
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if (state->unread_marker != 0)
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goto no_more_data; // can't advance past a marker
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if (bytes_in_buffer == 0) {
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if (! (*state->cinfo->src->fill_input_buffer) (state->cinfo))
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return FALSE;
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next_input_byte = state->cinfo->src->next_input_byte;
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bytes_in_buffer = state->cinfo->src->bytes_in_buffer;
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}
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bytes_in_buffer--;
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c = GETJOCTET(*next_input_byte++);
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// If it's 0xFF, check and discard stuffed zero byte
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if (c == 0xFF) {
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do {
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if (bytes_in_buffer == 0) {
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if (! (*state->cinfo->src->fill_input_buffer) (state->cinfo))
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return FALSE;
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next_input_byte = state->cinfo->src->next_input_byte;
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bytes_in_buffer = state->cinfo->src->bytes_in_buffer;
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}
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bytes_in_buffer--;
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c = GETJOCTET(*next_input_byte++);
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} while (c == 0xFF);
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if (c == 0) {
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// Found FF/00, which represents an FF data byte
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c = 0xFF;
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} else {
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// Oops, it's actually a marker indicating end of compressed data.
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// Better put it back for use later
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state->unread_marker = c;
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no_more_data:
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// There should be enough bits still left in the data segment;
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// if so, just break out of the outer while loop.
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if (bits_left >= nbits)
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break;
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// Uh-oh. Report corrupted data to user and stuff zeroes into
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// * the data stream, so that we can produce some kind of image.
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// * Note that this code will be repeated for each byte demanded
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// * for the rest of the segment. We use a nonvolatile flag to ensure
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// * that only one warning message appears.
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if (! *(state->printed_eod_ptr)) {
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WARNMS(state->cinfo, JWRN_HIT_MARKER);
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*(state->printed_eod_ptr) = TRUE;
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}
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c = 0; // insert a zero byte into bit buffer
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}
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}
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// OK, load c into get_buffer
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get_buffer = (get_buffer << 8) | c;
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bits_left += 8;
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}
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// Unload the local registers
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state->next_input_byte = next_input_byte;
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state->bytes_in_buffer = bytes_in_buffer;
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state->get_buffer = get_buffer;
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state->bits_left = bits_left;
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return TRUE;
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}
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// * Out-of-line code for Huffman code decoding.
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// * See jdhuff.h for info about usage.
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GLOBAL int
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jpeg_huff_decode (bitread_working_state * state,
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register bit_buf_type get_buffer, register int bits_left,
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d_derived_tbl * htbl, int min_bits)
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{
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register int l = min_bits;
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register INT32 code;
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// HUFF_DECODE has determined that the code is at least min_bits
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// bits LONG, so fetch that many bits in one swoop.
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CHECK_BIT_BUFFER(*state, l, return -1);
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code = GET_BITS(l);
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// Collect the rest of the Huffman code one bit at a time.
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// This is per Figure F.16 in the JPEG spec.
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while (code > htbl->maxcode[l]) {
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code <<= 1;
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CHECK_BIT_BUFFER(*state, 1, return -1);
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code |= GET_BITS(1);
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l++;
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}
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// Unload the local registers
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state->get_buffer = get_buffer;
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state->bits_left = bits_left;
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// With garbage input we may reach the sentinel value l = 17.
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if (l > 16) {
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WARNMS(state->cinfo, JWRN_HUFF_BAD_CODE);
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return 0; // fake a zero as the safest result
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}
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return htbl->pub->huffval[ htbl->valptr[l] +
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((int) (code - htbl->mincode[l])) ];
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}
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// * Figure F.12: extend sign bit.
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// * On some machines, a shift and add will be faster than a table lookup.
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#ifdef AVOID_TABLES
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#define HUFF_EXTEND(x,s) ((x) < (1<<((s)-1)) ? (x) + (((-1)<<(s)) + 1) : (x))
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#else
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#define HUFF_EXTEND(x,s) ((x) < extend_test[s] ? (x) + extend_offset[s] : (x))
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static const int extend_test[16] = // entry n is 2**(n-1)
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{ 0, 0x0001, 0x0002, 0x0004, 0x0008, 0x0010, 0x0020, 0x0040, 0x0080,
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0x0100, 0x0200, 0x0400, 0x0800, 0x1000, 0x2000, 0x4000 };
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static const int extend_offset[16] = // entry n is (-1 << n) + 1
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{ 0, ((-1)<<1) + 1, ((-1)<<2) + 1, ((-1)<<3) + 1, ((-1)<<4) + 1,
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((-1)<<5) + 1, ((-1)<<6) + 1, ((-1)<<7) + 1, ((-1)<<8) + 1,
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((-1)<<9) + 1, ((-1)<<10) + 1, ((-1)<<11) + 1, ((-1)<<12) + 1,
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((-1)<<13) + 1, ((-1)<<14) + 1, ((-1)<<15) + 1 };
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#endif // AVOID_TABLES
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// * Check for a restart marker & resynchronize decoder.
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// * Returns FALSE if must suspend.
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LOCAL boolean
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process_restart (j_decompress_ptr cinfo)
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{
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huff_entropy_ptr entropy = (huff_entropy_ptr) cinfo->entropy;
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int ci;
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// Throw away any unused bits remaining in bit buffer;
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// include any full bytes in next_marker's count of discarded bytes
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cinfo->marker->discarded_bytes += entropy->bitstate.bits_left / 8;
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entropy->bitstate.bits_left = 0;
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// Advance past the RSTn marker
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if (! (*cinfo->marker->read_restart_marker) (cinfo))
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return FALSE;
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// Re-initialize DC predictions to 0
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for (ci = 0; ci < cinfo->comps_in_scan; ci++)
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entropy->saved.last_dc_val[ci] = 0;
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// Reset restart counter
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entropy->restarts_to_go = cinfo->restart_interval;
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// Next segment can get another out-of-data warning
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entropy->bitstate.printed_eod = FALSE;
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return TRUE;
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}
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// * Decode and return one MCU's worth of Huffman-compressed coefficients.
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// * The coefficients are reordered from zigzag order into natural array order,
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// * but are not dequantized.
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// *
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// * The i'th block of the MCU is stored into the block pointed to by
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// * MCU_data[i]. WE ASSUME THIS AREA HAS BEEN ZEROED BY THE CALLER.
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// * (Wholesale zeroing is usually a little faster than retail...)
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// *
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// * Returns FALSE if data source requested suspension. In that case no
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// * changes have been made to permanent state. (Exception: some output
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// * coefficients may already have been assigned. This is harmless for
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// * this module, since we'll just re-assign them on the next call.)
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METHODDEF boolean
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decode_mcu (j_decompress_ptr cinfo, JBLOCKROW *MCU_data)
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{
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huff_entropy_ptr entropy = (huff_entropy_ptr) cinfo->entropy;
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register int s, k, r;
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int blkn, ci;
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JBLOCKROW block;
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BITREAD_STATE_VARS;
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savable_state state;
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d_derived_tbl * dctbl;
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d_derived_tbl * actbl;
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jpeg_component_info * compptr;
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// Process restart marker if needed; may have to suspend
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if (cinfo->restart_interval) {
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if (entropy->restarts_to_go == 0)
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if (! process_restart(cinfo))
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return FALSE;
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}
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// Load up working state
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BITREAD_LOAD_STATE(cinfo,entropy->bitstate);
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ASSIGN_STATE(state, entropy->saved);
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// Outer loop handles each block in the MCU
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for (blkn = 0; blkn < cinfo->blocks_in_MCU; blkn++) {
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block = MCU_data[blkn];
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ci = cinfo->MCU_membership[blkn];
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compptr = cinfo->cur_comp_info[ci];
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dctbl = entropy->dc_derived_tbls[compptr->dc_tbl_no];
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actbl = entropy->ac_derived_tbls[compptr->ac_tbl_no];
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// Decode a single block's worth of coefficients
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// Section F.2.2.1: decode the DC coefficient difference
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HUFF_DECODE(s, br_state, dctbl, return FALSE, label1);
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if (s) {
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CHECK_BIT_BUFFER(br_state, s, return FALSE);
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r = GET_BITS(s);
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s = HUFF_EXTEND(r, s);
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}
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// Shortcut if component's values are not interesting
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if (! compptr->component_needed)
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goto skip_ACs;
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// Convert DC difference to actual value, update last_dc_val
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s += state.last_dc_val[ci];
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state.last_dc_val[ci] = s;
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// Output the DC coefficient (assumes jpeg_natural_order[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, br_state, actbl, return FALSE, label2);
|
|
|
|
r = s >> 4;
|
|
s &= 15;
|
|
|
|
if (s) {
|
|
k += r;
|
|
CHECK_BIT_BUFFER(br_state, s, return FALSE);
|
|
r = GET_BITS(s);
|
|
s = HUFF_EXTEND(r, s);
|
|
// Output coefficient in natural (dezigzagged) order.
|
|
// * Note: the extra entries in jpeg_natural_order[] will save us
|
|
// * if k >= DCTSIZE2, which could happen if the data is corrupted.
|
|
(*block)[jpeg_natural_order[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, br_state, actbl, return FALSE, label3);
|
|
|
|
r = s >> 4;
|
|
s &= 15;
|
|
|
|
if (s) {
|
|
k += r;
|
|
CHECK_BIT_BUFFER(br_state, s, return FALSE);
|
|
DROP_BITS(s);
|
|
} else {
|
|
if (r != 15)
|
|
break;
|
|
k += 15;
|
|
}
|
|
}
|
|
|
|
}
|
|
}
|
|
|
|
// Completed MCU, so update state
|
|
BITREAD_SAVE_STATE(cinfo,entropy->bitstate);
|
|
ASSIGN_STATE(entropy->saved, state);
|
|
|
|
// 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;
|
|
}
|
|
}
|