652 строки
20 KiB
C
652 строки
20 KiB
C
/*
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* jdhuff.c
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*
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* Copyright (C) 1991-1997, 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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/* Precalculated info set up by start_pass for use in decode_mcu: */
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/* Pointers to derived tables to be used for each block within an MCU */
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d_derived_tbl * dc_cur_tbls[D_MAX_BLOCKS_IN_MCU];
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d_derived_tbl * ac_cur_tbls[D_MAX_BLOCKS_IN_MCU];
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/* Whether we care about the DC and AC coefficient values for each block */
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boolean dc_needed[D_MAX_BLOCKS_IN_MCU];
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boolean ac_needed[D_MAX_BLOCKS_IN_MCU];
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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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{
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huff_entropy_ptr entropy = (huff_entropy_ptr) cinfo->entropy;
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int ci, blkn, 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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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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/* 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, TRUE, dctbl,
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& entropy->dc_derived_tbls[dctbl]);
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jpeg_make_d_derived_tbl(cinfo, FALSE, 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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/* Precalculate decoding info for each block in an MCU of this scan */
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for (blkn = 0; blkn < cinfo->blocks_in_MCU; blkn++) {
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ci = cinfo->MCU_membership[blkn];
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compptr = cinfo->cur_comp_info[ci];
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/* Precalculate which table to use for each block */
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entropy->dc_cur_tbls[blkn] = entropy->dc_derived_tbls[compptr->dc_tbl_no];
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entropy->ac_cur_tbls[blkn] = entropy->ac_derived_tbls[compptr->ac_tbl_no];
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/* Decide whether we really care about the coefficient values */
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if (compptr->component_needed) {
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entropy->dc_needed[blkn] = TRUE;
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/* we don't need the ACs if producing a 1/8th-size image */
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entropy->ac_needed[blkn] = (compptr->DCT_scaled_size > 1);
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} else {
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entropy->dc_needed[blkn] = entropy->ac_needed[blkn] = FALSE;
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}
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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->pub.insufficient_data = 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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* This routine also performs some validation checks on the table.
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*
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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, boolean isDC, int tblno,
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d_derived_tbl ** pdtbl)
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{
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JHUFF_TBL *htbl;
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d_derived_tbl *dtbl;
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int p, i, l, si, numsymbols;
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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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/* Note that huffsize[] and huffcode[] are filled in code-length order,
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* paralleling the order of the symbols themselves in htbl->huffval[].
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*/
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/* Find the input Huffman table */
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if (tblno < 0 || tblno >= NUM_HUFF_TBLS)
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ERREXIT1(cinfo, JERR_NO_HUFF_TABLE, tblno);
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htbl =
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isDC ? cinfo->dc_huff_tbl_ptrs[tblno] : cinfo->ac_huff_tbl_ptrs[tblno];
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if (htbl == NULL)
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ERREXIT1(cinfo, JERR_NO_HUFF_TABLE, tblno);
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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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p = 0;
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for (l = 1; l <= 16; l++) {
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i = (int) htbl->bits[l];
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if (i < 0 || p + i > 256) /* protect against table overrun */
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ERREXIT(cinfo, JERR_BAD_HUFF_TABLE);
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while (i--)
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huffsize[p++] = (char) l;
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}
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huffsize[p] = 0;
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numsymbols = p;
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/* Figure C.2: generate the codes themselves */
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/* We also validate that the counts represent a legal Huffman code tree. */
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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 is now 1 more than the last code used for codelength si; but
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* it must still fit in si bits, since no code is allowed to be all ones.
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*/
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if (((INT32) code) >= (((INT32) 1) << si))
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ERREXIT(cinfo, JERR_BAD_HUFF_TABLE);
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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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/* valoffset[l] = huffval[] index of 1st symbol of code length l,
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* minus the minimum code of length l
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*/
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dtbl->valoffset[l] = (INT32) p - (INT32) huffcode[p];
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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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/* Validate symbols as being reasonable.
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* For AC tables, we make no check, but accept all byte values 0..255.
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* For DC tables, we require the symbols to be in range 0..15.
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* (Tighter bounds could be applied depending on the data depth and mode,
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* but this is sufficient to ensure safe decoding.)
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*/
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if (isDC) {
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for (i = 0; i < numsymbols; i++) {
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int sym = htbl->huffval[i];
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if (sym < 0 || sym > 15)
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ERREXIT(cinfo, JERR_BAD_HUFF_TABLE);
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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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{
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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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j_decompress_ptr cinfo = state->cinfo;
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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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/* We fail to do so only if we hit a marker or are forced to suspend. */
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if (cinfo->unread_marker == 0) { /* cannot advance past a marker */
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while (bits_left < MIN_GET_BITS) {
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register int c;
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/* Attempt to read a byte */
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if (bytes_in_buffer == 0) {
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if (! (*cinfo->src->fill_input_buffer) (cinfo))
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return FALSE;
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next_input_byte = cinfo->src->next_input_byte;
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bytes_in_buffer = 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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/* Loop here to discard any padding FF's on terminating marker,
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* so that we can save a valid unread_marker value. NOTE: we will
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* accept multiple FF's followed by a 0 as meaning a single FF data
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* byte. This data pattern is not valid according to the standard.
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*/
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do {
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if (bytes_in_buffer == 0) {
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if (! (*cinfo->src->fill_input_buffer) (cinfo))
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return FALSE;
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next_input_byte = cinfo->src->next_input_byte;
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bytes_in_buffer = 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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* Save the marker code for later use.
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* Fine point: it might appear that we should save the marker into
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* bitread working state, not straight into permanent state. But
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* once we have hit a marker, we cannot need to suspend within the
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* current MCU, because we will read no more bytes from the data
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* source. So it is OK to update permanent state right away.
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*/
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cinfo->unread_marker = c;
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/* See if we need to insert some fake zero bits. */
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goto no_more_bytes;
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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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} /* end while */
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} else {
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no_more_bytes:
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/* We get here if we've read the marker that terminates the compressed
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* data segment. There should be enough bits in the buffer register
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* to satisfy the request; if so, no problem.
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*/
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if (nbits > bits_left) {
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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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* We use a nonvolatile flag to ensure that only one warning message
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* appears per data segment.
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*/
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if (! cinfo->entropy->insufficient_data) {
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WARNMS(cinfo, JWRN_HIT_MARKER);
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cinfo->entropy->insufficient_data = TRUE;
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}
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/* Fill the buffer with zero bits */
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get_buffer <<= MIN_GET_BITS - bits_left;
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bits_left = MIN_GET_BITS;
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}
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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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{
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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[ (int) (code + htbl->valoffset[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.
|
|
* 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->bitstate.bits_left / 8;
|
|
entropy->bitstate.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;
|
|
|
|
/* Reset out-of-data flag, unless read_restart_marker left us smack up
|
|
* against a marker. In that case we will end up treating the next data
|
|
* segment as empty, and we can avoid producing bogus output pixels by
|
|
* leaving the flag set.
|
|
*/
|
|
if (cinfo->unread_marker == 0)
|
|
entropy->pub.insufficient_data = FALSE;
|
|
|
|
return TRUE;
|
|
}
|
|
|
|
|
|
/*
|
|
* 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, since we'll just re-assign them on the next call.)
|
|
*/
|
|
|
|
METHODDEF(boolean)
|
|
decode_mcu (j_decompress_ptr cinfo, JBLOCKROW *MCU_data)
|
|
{
|
|
huff_entropy_ptr entropy = (huff_entropy_ptr) cinfo->entropy;
|
|
int blkn;
|
|
BITREAD_STATE_VARS;
|
|
savable_state state;
|
|
|
|
/* 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;
|
|
}
|
|
|
|
/* If we've run out of data, just leave the MCU set to zeroes.
|
|
* This way, we return uniform gray for the remainder of the segment.
|
|
*/
|
|
if (! entropy->pub.insufficient_data) {
|
|
|
|
/* Load up working state */
|
|
BITREAD_LOAD_STATE(cinfo,entropy->bitstate);
|
|
ASSIGN_STATE(state, entropy->saved);
|
|
|
|
/* Outer loop handles each block in the MCU */
|
|
|
|
for (blkn = 0; blkn < cinfo->blocks_in_MCU; blkn++) {
|
|
JBLOCKROW block = MCU_data[blkn];
|
|
d_derived_tbl * dctbl = entropy->dc_cur_tbls[blkn];
|
|
d_derived_tbl * actbl = entropy->ac_cur_tbls[blkn];
|
|
register int s, k, r;
|
|
|
|
/* 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);
|
|
}
|
|
|
|
if (entropy->dc_needed[blkn]) {
|
|
/* Convert DC difference to actual value, update last_dc_val */
|
|
int ci = cinfo->MCU_membership[blkn];
|
|
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;
|
|
}
|
|
|
|
if (entropy->ac_needed[blkn]) {
|
|
|
|
/* 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 {
|
|
|
|
/* 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;
|
|
}
|
|
}
|