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587 lines
20 KiB
C++
587 lines
20 KiB
C++
/*
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* 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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*/
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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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/*
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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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*/
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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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*/
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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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*/
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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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/*
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* Initialize for a Huffman-compressed scan.
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*/
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METHODDEF void
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start_pass_huff_decoder( j_decompress_ptr cinfo ) {
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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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*/
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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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}
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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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}
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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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}
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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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/*
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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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*/
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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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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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}
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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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}
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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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*/
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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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/*
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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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*/
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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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/* 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;
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} /* 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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}
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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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}
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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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}
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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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*/
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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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/*
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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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*/
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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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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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/*
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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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*/
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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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/*
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* Check for a restart marker & resynchronize decoder.
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* Returns FALSE if must suspend.
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*/
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LOCAL boolean
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process_restart( j_decompress_ptr cinfo ) {
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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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}
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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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}
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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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/*
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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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*/
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METHODDEF boolean
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decode_mcu( j_decompress_ptr cinfo, JBLOCKROW * MCU_data ) {
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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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}
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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];
|
|
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, br_state, dctbl, return FALSE, label1 );
|
|
if ( s ) {
|
|
CHECK_BIT_BUFFER( br_state, s, return FALSE );
|
|
|
|
r = GET_BITS( 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.last_dc_val[ci];
|
|
state.last_dc_val[ci] = s;
|
|
/* 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;
|
|
}
|
|
}
|