text: /*
   * jdshuff.c
   *
   * Copyright (C) 1991-1998, 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 sequential 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 "jinclude16.h"
  #include "jpeglib16.h"
  #include "jlossy16.h"		/* Private declarations for lossy codec */
  #include "jdhuff16.h"		/* Declarations shared with jd*huff.c */
  
  
  /*
   * Private entropy decoder object for 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 {
    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).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
  #endif
  
  
  typedef struct {
    huffd_common_fields;		/* Fields shared with other entropy decoders */
  
    /* These fields are loaded into local variables at start of each MCU.
     * In case of suspension, we exit WITHOUT updating them.
     */
    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 * dc_derived_tbls[NUM_HUFF_TBLS];
    d_derived_tbl * ac_derived_tbls[NUM_HUFF_TBLS];
  
    /* Precalculated info set up by start_pass for use in decode_mcu: */
  
    /* Pointers to derived tables to be used for each block within an MCU */
    d_derived_tbl * dc_cur_tbls[D_MAX_DATA_UNITS_IN_MCU];
    d_derived_tbl * ac_cur_tbls[D_MAX_DATA_UNITS_IN_MCU];
    /* Whether we care about the DC and AC coefficient values for each block */
    boolean dc_needed[D_MAX_DATA_UNITS_IN_MCU];
    boolean ac_needed[D_MAX_DATA_UNITS_IN_MCU];
  } shuff_entropy_decoder;
  
  typedef shuff_entropy_decoder * shuff_entropy_ptr;
  
  
  /*
   * Initialize for a Huffman-compressed scan.
   */
  
  METHODDEF(void)
  start_pass_huff_decoder (j_decompress_ptr cinfo)
  {
    j_lossy_d_ptr lossyd = (j_lossy_d_ptr) cinfo->codec;
    shuff_entropy_ptr entropy = (shuff_entropy_ptr) lossyd->entropy_private;
    int ci, blkn, dctbl, actbl;
    jpeg_component_info * compptr;
  
    /* Check that the scan parameters Ss, Se, Ah/Al are OK for sequential JPEG.
     * This ought to be an error condition, but we make it a warning because
     * there are some baseline files out there with all zeroes in these bytes.
     */
    if (cinfo->Ss != 0 || cinfo->Se != DCTSIZE2-1 ||
        cinfo->Ah != 0 || cinfo->Al != 0)
      WARNMS(cinfo, JWRN_NOT_SEQUENTIAL);
  
    for (ci = 0; ci < cinfo->comps_in_scan; ci++) {
      compptr = cinfo->cur_comp_info[ci];
      dctbl = compptr->dc_tbl_no;
      actbl = compptr->ac_tbl_no;
      /* Compute derived values for Huffman tables */
      /* We may do this more than once for a table, but it's not expensive */
      jpeg_make_d_derived_tbl(cinfo, TRUE, dctbl,
  			    & entropy->dc_derived_tbls[dctbl]);
      jpeg_make_d_derived_tbl(cinfo, FALSE, actbl,
  			    & entropy->ac_derived_tbls[actbl]);
      /* Initialize DC predictions to 0 */
      entropy->saved.last_dc_val[ci] = 0;
    }
  
    /* Precalculate decoding info for each block in an MCU of this scan */
    for (blkn = 0; blkn < cinfo->data_units_in_MCU; blkn++) {
      ci = cinfo->MCU_membership[blkn];
      compptr = cinfo->cur_comp_info[ci];
      /* Precalculate which table to use for each block */
      entropy->dc_cur_tbls[blkn] = entropy->dc_derived_tbls[compptr->dc_tbl_no];
      entropy->ac_cur_tbls[blkn] = entropy->ac_derived_tbls[compptr->ac_tbl_no];
      /* Decide whether we really care about the coefficient values */
      if (compptr->component_needed) {
        entropy->dc_needed[blkn] = TRUE;
        /* we don't need the ACs if producing a 1/8th-size image */
        entropy->ac_needed[blkn] = (compptr->codec_data_unit > 1);
      } else {
        entropy->dc_needed[blkn] = entropy->ac_needed[blkn] = FALSE;
      }
    }
  
    /* Initialize bitread state variables */
    entropy->bitstate.bits_left = 0;
    entropy->bitstate.get_buffer = 0; /* unnecessary, but keeps Purify quiet */
    entropy->insufficient_data = FALSE;
  
    /* 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, ((-1u)<<1) + 1, ((-1u)<<2) + 1, ((-1u)<<3) + 1, ((-1u)<<4) + 1,
      ((-1u)<<5) + 1, ((-1u)<<6) + 1, ((-1u)<<7) + 1, ((-1u)<<8) + 1,
      ((-1u)<<9) + 1, ((-1u)<<10) + 1, ((-1u)<<11) + 1, ((-1u)<<12) + 1,
      ((-1u)<<13) + 1, ((-1u)<<14) + 1, ((-1u)<<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)
  {
    j_lossy_d_ptr lossyd = (j_lossy_d_ptr) cinfo->codec;
    shuff_entropy_ptr entropy = (shuff_entropy_ptr) lossyd->entropy_private;
    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->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)
  {
    j_lossy_d_ptr lossyd = (j_lossy_d_ptr) cinfo->codec;
    shuff_entropy_ptr entropy = (shuff_entropy_ptr) lossyd->entropy_private;
    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->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->data_units_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_shuff_decoder (j_decompress_ptr cinfo)
  {
    j_lossy_d_ptr lossyd = (j_lossy_d_ptr) cinfo->codec;
    shuff_entropy_ptr entropy;
    int i;
  
    entropy = (shuff_entropy_ptr)
      (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
  				SIZEOF(shuff_entropy_decoder));
    lossyd->entropy_private = (void *) entropy;
    lossyd->entropy_start_pass = start_pass_huff_decoder;
    lossyd->entropy_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;
    }
  }
  