/* * jdphuff.c * * Copyright (C) 1995-1997, Thomas G. Lane. * This file is part of the Independent JPEG Group's software. * For conditions of distribution and use, see the accompanying README file. * * This file contains Huffman entropy decoding routines for progressive JPEG. * * Much of the complexity here has to do with supporting input suspension. * If the data source module demands suspension, we want to be able to back * up to the start of the current MCU.  To do this, we copy state variables * into local working storage, and update them back to the permanent * storage only upon successful completion of an MCU. */#define JPEG_INTERNALS#include "jinclude.h"#include "jpeglib.h"#include "jdhuff.h"		/* Declarations shared with jdhuff.c */#ifdef D_PROGRESSIVE_SUPPORTED/* * Expanded entropy decoder object for progressive Huffman decoding. * * The savable_state subrecord contains fields that change within an MCU, * but must not be updated permanently until we complete the MCU. */typedef struct {  unsigned int EOBRUN;			/* remaining EOBs in EOBRUN */  int last_dc_val[MAX_COMPS_IN_SCAN];	/* last DC coef for each component */} savable_state;/* This macro is to work around compilers with missing or broken * structure assignment.  You'll need to fix this code if you have * such a compiler and you change MAX_COMPS_IN_SCAN. */#ifndef NO_STRUCT_ASSIGN#define ASSIGN_STATE(dest,src)  ((dest) = (src))#else#if MAX_COMPS_IN_SCAN == 4#define ASSIGN_STATE(dest,src)  \	((dest).EOBRUN = (src).EOBRUN, \	 (dest).last_dc_val[0] = (src).last_dc_val[0], \	 (dest).last_dc_val[1] = (src).last_dc_val[1], \	 (dest).last_dc_val[2] = (src).last_dc_val[2], \	 (dest).last_dc_val[3] = (src).last_dc_val[3])#endif#endiftypedef struct {  struct jpeg_entropy_decoder pub; /* public fields */  /* These fields are loaded into local variables at start of each MCU.   * In case of suspension, we exit WITHOUT updating them.   */  bitread_perm_state bitstate;	/* Bit buffer at start of MCU */  savable_state saved;		/* Other state at start of MCU */  /* These fields are NOT loaded into local working state. */  unsigned int restarts_to_go;	/* MCUs left in this restart interval */  /* Pointers to derived tables (these workspaces have image lifespan) */  d_derived_tbl * derived_tbls[NUM_HUFF_TBLS];  d_derived_tbl * ac_derived_tbl; /* active table during an AC scan */} phuff_entropy_decoder;typedef phuff_entropy_decoder * phuff_entropy_ptr;/* Forward declarations */METHODDEF(boolean) decode_mcu_DC_first JPP((j_decompress_ptr cinfo,					    JBLOCKROW *MCU_data));METHODDEF(boolean) decode_mcu_AC_first JPP((j_decompress_ptr cinfo,					    JBLOCKROW *MCU_data));METHODDEF(boolean) decode_mcu_DC_refine JPP((j_decompress_ptr cinfo,					     JBLOCKROW *MCU_data));METHODDEF(boolean) decode_mcu_AC_refine JPP((j_decompress_ptr cinfo,					     JBLOCKROW *MCU_data));/* * Initialize for a Huffman-compressed scan. */METHODDEF(void)start_pass_phuff_decoder (j_decompress_ptr cinfo){  phuff_entropy_ptr entropy = (phuff_entropy_ptr) cinfo->entropy;  boolean is_DC_band, bad;  int ci, coefi, tbl;  int *coef_bit_ptr;  jpeg_component_info * compptr;  is_DC_band = (cinfo->Ss == 0);  /* Validate scan parameters */  bad = FALSE;  if (is_DC_band) {    if (cinfo->Se != 0)      bad = TRUE;  } else {    /* need not check Ss/Se < 0 since they came from unsigned bytes */    if (cinfo->Ss > cinfo->Se || cinfo->Se >= DCTSIZE2)      bad = TRUE;    /* AC scans may have only one component */    if (cinfo->comps_in_scan != 1)      bad = TRUE;  }  if (cinfo->Ah != 0) {    /* Successive approximation refinement scan: must have Al = Ah-1. */    if (cinfo->Al != cinfo->Ah-1)      bad = TRUE;  }  if (cinfo->Al > 13)		/* need not check for < 0 */    bad = TRUE;  /* Arguably the maximum Al value should be less than 13 for 8-bit precision,   * but the spec doesn't say so, and we try to be liberal about what we   * accept.  Note: large Al values could result in out-of-range DC   * coefficients during early scans, leading to bizarre displays due to   * overflows in the IDCT math.  But we won't crash.   */  if (bad)    ERREXIT4(cinfo, JERR_BAD_PROGRESSION,	     cinfo->Ss, cinfo->Se, cinfo->Ah, cinfo->Al);  /* Update progression status, and verify that scan order is legal.   * Note that inter-scan inconsistencies are treated as warnings   * not fatal errors ... not clear if this is right way to behave.   */  for (ci = 0; ci < cinfo->comps_in_scan; ci++) {    int cindex = cinfo->cur_comp_info[ci]->component_index;    coef_bit_ptr = & cinfo->coef_bits[cindex][0];    if (!is_DC_band && coef_bit_ptr[0] < 0) /* AC without prior DC scan */      WARNMS2(cinfo, JWRN_BOGUS_PROGRESSION, cindex, 0);    for (coefi = cinfo->Ss; coefi <= cinfo->Se; coefi++) {      int expected = (coef_bit_ptr[coefi] < 0) ? 0 : coef_bit_ptr[coefi];      if (cinfo->Ah != expected)	WARNMS2(cinfo, JWRN_BOGUS_PROGRESSION, cindex, coefi);      coef_bit_ptr[coefi] = cinfo->Al;    }  }  /* Select MCU decoding routine */  if (cinfo->Ah == 0) {    if (is_DC_band)      entropy->pub.decode_mcu = decode_mcu_DC_first;    else      entropy->pub.decode_mcu = decode_mcu_AC_first;  } else {    if (is_DC_band)      entropy->pub.decode_mcu = decode_mcu_DC_refine;    else      entropy->pub.decode_mcu = decode_mcu_AC_refine;  }  for (ci = 0; ci < cinfo->comps_in_scan; ci++) {    compptr = cinfo->cur_comp_info[ci];    /* Make sure requested tables are present, and compute derived tables.     * We may build same derived table more than once, but it's not expensive.     */    if (is_DC_band) {      if (cinfo->Ah == 0) {	/* DC refinement needs no table */	tbl = compptr->dc_tbl_no;	jpeg_make_d_derived_tbl(cinfo, TRUE, tbl,				& entropy->derived_tbls[tbl]);      }    } else {      tbl = compptr->ac_tbl_no;      jpeg_make_d_derived_tbl(cinfo, FALSE, tbl,			      & entropy->derived_tbls[tbl]);      /* remember the single active table */      entropy->ac_derived_tbl = entropy->derived_tbls[tbl];    }    /* Initialize DC predictions to 0 */    entropy->saved.last_dc_val[ci] = 0;  }  /* Initialize bitread state variables */  entropy->bitstate.bits_left = 0;  entropy->bitstate.get_buffer = 0; /* unnecessary, but keeps Purify quiet */  entropy->pub.insufficient_data = FALSE;  /* Initialize private state variables */  entropy->saved.EOBRUN = 0;  /* Initialize restart counter */  entropy->restarts_to_go = cinfo->restart_interval;}/* * Figure F.12: extend sign bit. * On some machines, a shift and add will be faster than a table lookup. */#ifdef AVOID_TABLES#define HUFF_EXTEND(x,s)  ((x) < (1<<((s)-1)) ? (x) + (((-1)<<(s)) + 1) : (x))#else#define HUFF_EXTEND(x,s)  ((x) < extend_test[s] ? (x) + extend_offset[s] : (x))static const int extend_test[16] =   /* entry n is 2**(n-1) */  { 0, 0x0001, 0x0002, 0x0004, 0x0008, 0x0010, 0x0020, 0x0040, 0x0080,    0x0100, 0x0200, 0x0400, 0x0800, 0x1000, 0x2000, 0x4000 };static const int extend_offset[16] = /* entry n is (-1 << n) + 1 */  { 0, ((-1)<<1) + 1, ((-1)<<2) + 1, ((-1)<<3) + 1, ((-1)<<4) + 1,    ((-1)<<5) + 1, ((-1)<<6) + 1, ((-1)<<7) + 1, ((-1)<<8) + 1,    ((-1)<<9) + 1, ((-1)<<10) + 1, ((-1)<<11) + 1, ((-1)<<12) + 1,    ((-1)<<13) + 1, ((-1)<<14) + 1, ((-1)<<15) + 1 };#endif /* AVOID_TABLES *//* * Check for a restart marker & resynchronize decoder. * Returns FALSE if must suspend. */LOCAL(boolean)process_restart (j_decompress_ptr cinfo){  phuff_entropy_ptr entropy = (phuff_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;  /* Re-init EOB run count, too */  entropy->saved.EOBRUN = 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;}/* * Huffman MCU decoding. * Each of these routines decodes and returns 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 IS INITIALLY ZEROED BY THE CALLER. * * We return 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 * spectral selection, since we'll just re-assign them on the next call. * Successive approximation AC refinement has to be more careful, however.) *//* * MCU decoding for DC initial scan (either spectral selection, * or first pass of successive approximation). */METHODDEF(boolean)decode_mcu_DC_first (j_decompress_ptr cinfo, JBLOCKROW *MCU_data){     phuff_entropy_ptr entropy = (phuff_entropy_ptr) cinfo->entropy;  int Al = cinfo->Al;  register int s, r;  int blkn, ci;  JBLOCKROW block;  BITREAD_STATE_VARS;  savable_state state;  d_derived_tbl * tbl;  jpeg_component_info * compptr;  /* Process restart marker if needed; may have to suspend */  if (cinfo->restart_interval) {    if (entropy->restarts_to_go == 0)      if (! process_restart(cinfo))	return FALSE;  }  /* 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++) {      block = MCU_data[blkn];      ci = cinfo->MCU_membership[blkn];      compptr = cinfo->cur_comp_info[ci];      tbl = entropy->derived_tbls[compptr->dc_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, tbl, return FALSE, label1);      if (s) {	CHECK_BIT_BUFFER(br_state, s, return FALSE);	r = GET_BITS(s);	s = HUFF_EXTEND(r, s);      }      /* Convert DC difference to actual value, update last_dc_val */      s += state.last_dc_val[ci];      state.last_dc_val[ci] = s;      /* Scale and output the coefficient (assumes jpeg_natural_order[0]=0) */