/*

 * 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 "jinclude12.h"

#include "jpeglib12.h"

#include "jlossy12.h"       /* Private declarations for lossy codec */

#include "jdhuff12.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 };

/*

 * Originally, a -1 was shifted but since shifting a negative value is

 * undefined behavior, now "~0U" (bit-wise NOT unsigned int 0) is used,

 * shifted and casted to an int. The result is the same, of course.

 */

static const int extend_offset[16] = /* entry n is (-1 << n) + 1 */

  { 0, (int)((~0U)<<1) + 1, (int)((~0U)<<2) + 1, (int)((~0U)<<3) + 1, (int)((~0U)<<4) + 1,

    (int)((~0U)<<5) + 1, (int)((~0U)<<6) + 1, (int)((~0U)<<7) + 1, (int)((~0U)<<8) + 1,

    (int)((~0U)<<9) + 1, (int)((~0U)<<10) + 1, (int)((~0U)<<11) + 1, (int)((~0U)<<12) + 1,

    (int)((~0U)<<13) + 1, (int)((~0U)<<14) + 1, (int)((~0U)<<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 += (unsigned int)(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) {

    /* DC categories above 15 are undefined for DCT-based coding */

    /* (ISO 10918-1 Tables F.1 and F.6) and would index extend_test[]/ */

    /* extend_offset[] out of bounds; treat such a Huffman code as */

    /* corrupt data instead of reading past the array. */

    if (s > 15) {

      WARNMS(cinfo, JWRN_HUFF_BAD_CODE);

      s = 0;

    } else {

      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;

  }

}