/*

 * jchuff.c

 *

 * Copyright (C) 1991-1997, Thomas G. Lane.

 * Modified 2006-2009 by Guido Vollbeding.

 * 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 encoding routines.

 * Both sequential and progressive modes are supported in this single module.

 *

 * Much of the complexity here has to do with supporting output suspension.

 * If the data destination 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 JPEG objects only upon successful completion of an MCU.

 *

 * We do not support output suspension for the progressive JPEG mode, since

 * the library currently does not allow multiple-scan files to be written

 * with output suspension.

 */

#define JPEG_INTERNALS

#include "jinclude.h"

#include "jpeglib.h"

/* The legal range of a DCT coefficient is

 *  -1024 .. +1023  for 8-bit data;

 * -16384 .. +16383 for 12-bit data.

 * Hence the magnitude should always fit in 10 or 14 bits respectively.

 */

#if BITS_IN_JSAMPLE == 8

#define MAX_COEF_BITS 10

#else

#define MAX_COEF_BITS 14

#endif

/* Derived data constructed for each Huffman table */

typedef struct {

  unsigned int ehufco[256];	/* code for each symbol */

  char ehufsi[256];		/* length of code for each symbol */

  /* If no code has been allocated for a symbol S, ehufsi[S] contains 0 */

} c_derived_tbl;

/* Expanded entropy encoder object for Huffman encoding.

 *

 * The savable_state subrecord contains fields that change within an MCU,

 * but must not be updated permanently until we complete the MCU.

 */

typedef struct {

  INT32 put_buffer;		/* current bit-accumulation buffer */

  int put_bits;			/* # of bits now in it */

  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).put_buffer = (src).put_buffer, \

	 (dest).put_bits = (src).put_bits, \

	 (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 {

  struct jpeg_entropy_encoder pub; /* public fields */

  savable_state saved;		/* Bit buffer & DC 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 */

  int next_restart_num;		/* next restart number to write (0-7) */

  /* Pointers to derived tables (these workspaces have image lifespan) */

  c_derived_tbl * dc_derived_tbls[NUM_HUFF_TBLS];

  c_derived_tbl * ac_derived_tbls[NUM_HUFF_TBLS];

  /* Statistics tables for optimization */

  long * dc_count_ptrs[NUM_HUFF_TBLS];

  long * ac_count_ptrs[NUM_HUFF_TBLS];

  /* Following fields used only in progressive mode */

  /* Mode flag: TRUE for optimization, FALSE for actual data output */

  boolean gather_statistics;

  /* next_output_byte/free_in_buffer are local copies of cinfo->dest fields.

   */

  JOCTET * next_output_byte;	/* => next byte to write in buffer */

  size_t free_in_buffer;	/* # of byte spaces remaining in buffer */

  j_compress_ptr cinfo;		/* link to cinfo (needed for dump_buffer) */

  /* Coding status for AC components */

  int ac_tbl_no;		/* the table number of the single component */

  unsigned int EOBRUN;		/* run length of EOBs */

  unsigned int BE;		/* # of buffered correction bits before MCU */

  char * bit_buffer;		/* buffer for correction bits (1 per char) */

  /* packing correction bits tightly would save some space but cost time... */

} huff_entropy_encoder;

typedef huff_entropy_encoder * huff_entropy_ptr;

/* Working state while writing an MCU (sequential mode).

 * This struct contains all the fields that are needed by subroutines.

 */

typedef struct {

  JOCTET * next_output_byte;	/* => next byte to write in buffer */

  size_t free_in_buffer;	/* # of byte spaces remaining in buffer */

  savable_state cur;		/* Current bit buffer & DC state */

  j_compress_ptr cinfo;		/* dump_buffer needs access to this */

} working_state;

/* MAX_CORR_BITS is the number of bits the AC refinement correction-bit

 * buffer can hold.  Larger sizes may slightly improve compression, but

 * 1000 is already well into the realm of overkill.

 * The minimum safe size is 64 bits.

 */

#define MAX_CORR_BITS  1000	/* Max # of correction bits I can buffer */

/* IRIGHT_SHIFT is like RIGHT_SHIFT, but works on int rather than INT32.

 * We assume that int right shift is unsigned if INT32 right shift is,

 * which should be safe.

 */

#ifdef RIGHT_SHIFT_IS_UNSIGNED

#define ISHIFT_TEMPS	int ishift_temp;

#define IRIGHT_SHIFT(x,shft)  \

	((ishift_temp = (x)) < 0 ? \

	 (ishift_temp >> (shft)) | ((~0) << (16-(shft))) : \

	 (ishift_temp >> (shft)))

#else

#define ISHIFT_TEMPS

#define IRIGHT_SHIFT(x,shft)	((x) >> (shft))

#endif

/*

 * Compute the derived values for a Huffman table.

 * This routine also performs some validation checks on the table.

 */

LOCAL(void)

jpeg_make_c_derived_tbl (j_compress_ptr cinfo, boolean isDC, int tblno,

			 c_derived_tbl ** pdtbl)

{

  JHUFF_TBL *htbl;

  c_derived_tbl *dtbl;

  int p, i, l, lastp, si, maxsymbol;

  char huffsize[257];

  unsigned int huffcode[257];

  unsigned int code;

  /* Note that huffsize[] and huffcode[] are filled in code-length order,

   * paralleling the order of the symbols themselves in htbl->huffval[].

   */

  /* Find the input Huffman table */

  if (tblno < 0 || tblno >= NUM_HUFF_TBLS)

    ERREXIT1(cinfo, JERR_NO_HUFF_TABLE, tblno);

  htbl =

    isDC ? cinfo->dc_huff_tbl_ptrs[tblno] : cinfo->ac_huff_tbl_ptrs[tblno];

  if (htbl == NULL)

    ERREXIT1(cinfo, JERR_NO_HUFF_TABLE, tblno);

  /* Allocate a workspace if we haven't already done so. */

  if (*pdtbl == NULL)

    *pdtbl = (c_derived_tbl *)

      (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,

				  SIZEOF(c_derived_tbl));

  dtbl = *pdtbl;

  /* Figure C.1: make table of Huffman code length for each symbol */

  p = 0;

  for (l = 1; l <= 16; l++) {

    i = (int) htbl->bits[l];

    if (i < 0 || p + i > 256)	/* protect against table overrun */

      ERREXIT(cinfo, JERR_BAD_HUFF_TABLE);

    while (i--)

      huffsize[p++] = (char) l;

  }

  huffsize[p] = 0;

  lastp = p;

  /* Figure C.2: generate the codes themselves */

  /* We also validate that the counts represent a legal Huffman code tree. */

  code = 0;

  si = huffsize[0];

  p = 0;

  while (huffsize[p]) {

    while (((int) huffsize[p]) == si) {

      huffcode[p++] = code;

      code++;

    }

    /* code is now 1 more than the last code used for codelength si; but

     * it must still fit in si bits, since no code is allowed to be all ones.

     */

    if (((INT32) code) >= (((INT32) 1) << si))

      ERREXIT(cinfo, JERR_BAD_HUFF_TABLE);

    code <<= 1;

    si++;

  }

  /* Figure C.3: generate encoding tables */

  /* These are code and size indexed by symbol value */

  /* Set all codeless symbols to have code length 0;

   * this lets us detect duplicate VAL entries here, and later

   * allows emit_bits to detect any attempt to emit such symbols.

   */

  MEMZERO(dtbl->ehufsi, SIZEOF(dtbl->ehufsi));

  /* This is also a convenient place to check for out-of-range

   * and duplicated VAL entries.  We allow 0..255 for AC symbols

   * but only 0..15 for DC.  (We could constrain them further

   * based on data depth and mode, but this seems enough.)

   */

  maxsymbol = isDC ? 15 : 255;

  for (p = 0; p < lastp; p++) {

    i = htbl->huffval[p];

    if (i < 0 || i > maxsymbol || dtbl->ehufsi[i])

      ERREXIT(cinfo, JERR_BAD_HUFF_TABLE);

    dtbl->ehufco[i] = huffcode[p];

    dtbl->ehufsi[i] = huffsize[p];

  }

}

/* Outputting bytes to the file.

 * NB: these must be called only when actually outputting,

 * that is, entropy->gather_statistics == FALSE.

 */

/* Emit a byte, taking 'action' if must suspend. */

#define emit_byte_s(state,val,action)  \

	{ *(state)->next_output_byte++ = (JOCTET) (val);  \

	  if (--(state)->free_in_buffer == 0)  \

	    if (! dump_buffer_s(state))  \

	      { action; } }

/* Emit a byte */

#define emit_byte_e(entropy,val)  \

	{ *(entropy)->next_output_byte++ = (JOCTET) (val);  \

	  if (--(entropy)->free_in_buffer == 0)  \

	    dump_buffer_e(entropy); }

LOCAL(boolean)

dump_buffer_s (working_state * state)

/* Empty the output buffer; return TRUE if successful, FALSE if must suspend */

{

  struct jpeg_destination_mgr * dest = state->cinfo->dest;

  if (! (*dest->empty_output_buffer) (state->cinfo))

    return FALSE;

  /* After a successful buffer dump, must reset buffer pointers */

  state->next_output_byte = dest->next_output_byte;

  state->free_in_buffer = dest->free_in_buffer;

  return TRUE;

}

LOCAL(void)

dump_buffer_e (huff_entropy_ptr entropy)

/* Empty the output buffer; we do not support suspension in this case. */

{

  struct jpeg_destination_mgr * dest = entropy->cinfo->dest;

  if (! (*dest->empty_output_buffer) (entropy->cinfo))

    ERREXIT(entropy->cinfo, JERR_CANT_SUSPEND);

  /* After a successful buffer dump, must reset buffer pointers */

  entropy->next_output_byte = dest->next_output_byte;

  entropy->free_in_buffer = dest->free_in_buffer;

}

/* Outputting bits to the file */

/* Only the right 24 bits of put_buffer are used; the valid bits are

 * left-justified in this part.  At most 16 bits can be passed to emit_bits

 * in one call, and we never retain more than 7 bits in put_buffer

 * between calls, so 24 bits are sufficient.

 */

INLINE

LOCAL(boolean)

emit_bits_s (working_state * state, unsigned int code, int size)

/* Emit some bits; return TRUE if successful, FALSE if must suspend */

{

  /* This routine is heavily used, so it's worth coding tightly. */

  register INT32 put_buffer = (INT32) code;

  register int put_bits = state->cur.put_bits;

  /* if size is 0, caller used an invalid Huffman table entry */

  if (size == 0)

    ERREXIT(state->cinfo, JERR_HUFF_MISSING_CODE);

  put_buffer &= (((INT32) 1)<

  put_bits += size;		/* new number of bits in buffer */

  put_buffer <<= 24 - put_bits; /* align incoming bits */

  put_buffer |= state->cur.put_buffer; /* and merge with old buffer contents */

  while (put_bits >= 8) {

    int c = (int) ((put_buffer >> 16) & 0xFF);

    emit_byte_s(state, c, return FALSE);

    if (c == 0xFF) {		/* need to stuff a zero byte? */

      emit_byte_s(state, 0, return FALSE);

    }

    put_buffer <<= 8;

    put_bits -= 8;

  }

  state->cur.put_buffer = put_buffer; /* update state variables */

  state->cur.put_bits = put_bits;

  return TRUE;

}

INLINE

LOCAL(void)

emit_bits_e (huff_entropy_ptr entropy, unsigned int code, int size)

/* Emit some bits, unless we are in gather mode */

{

  /* This routine is heavily used, so it's worth coding tightly. */

  register INT32 put_buffer = (INT32) code;

  register int put_bits = entropy->saved.put_bits;

  /* if size is 0, caller used an invalid Huffman table entry */

  if (size == 0)

    ERREXIT(entropy->cinfo, JERR_HUFF_MISSING_CODE);

  if (entropy->gather_statistics)

    return;			/* do nothing if we're only getting stats */

  put_buffer &= (((INT32) 1)<

  put_bits += size;		/* new number of bits in buffer */

  put_buffer <<= 24 - put_bits; /* align incoming bits */

  /* and merge with old buffer contents */

  put_buffer |= entropy->saved.put_buffer;

  while (put_bits >= 8) {

    int c = (int) ((put_buffer >> 16) & 0xFF);

    emit_byte_e(entropy, c);

    if (c == 0xFF) {		/* need to stuff a zero byte? */

      emit_byte_e(entropy, 0);

    }

    put_buffer <<= 8;

    put_bits -= 8;

  }

  entropy->saved.put_buffer = put_buffer; /* update variables */

  entropy->saved.put_bits = put_bits;

}

LOCAL(boolean)

flush_bits_s (working_state * state)

{

  if (! emit_bits_s(state, 0x7F, 7)) /* fill any partial byte with ones */

    return FALSE;

  state->cur.put_buffer = 0;	     /* and reset bit-buffer to empty */

  state->cur.put_bits = 0;

  return TRUE;

}

LOCAL(void)

flush_bits_e (huff_entropy_ptr entropy)

{

  emit_bits_e(entropy, 0x7F, 7); /* fill any partial byte with ones */

  entropy->saved.put_buffer = 0; /* and reset bit-buffer to empty */

  entropy->saved.put_bits = 0;

}

/*

 * Emit (or just count) a Huffman symbol.

 */

INLINE

LOCAL(void)

emit_dc_symbol (huff_entropy_ptr entropy, int tbl_no, int symbol)

{

  if (entropy->gather_statistics)

    entropy->dc_count_ptrs[tbl_no][symbol]++;

  else {

    c_derived_tbl * tbl = entropy->dc_derived_tbls[tbl_no];

    emit_bits_e(entropy, tbl->ehufco[symbol], tbl->ehufsi[symbol]);

  }

}

INLINE

LOCAL(void)

emit_ac_symbol (huff_entropy_ptr entropy, int tbl_no, int symbol)

{

  if (entropy->gather_statistics)

    entropy->ac_count_ptrs[tbl_no][symbol]++;

  else {

    c_derived_tbl * tbl = entropy->ac_derived_tbls[tbl_no];

    emit_bits_e(entropy, tbl->ehufco[symbol], tbl->ehufsi[symbol]);

  }

}

/*

 * Emit bits from a correction bit buffer.

 */

LOCAL(void)

emit_buffered_bits (huff_entropy_ptr entropy, char * bufstart,

		    unsigned int nbits)

{

  if (entropy->gather_statistics)

    return;			/* no real work */

  while (nbits > 0) {

    emit_bits_e(entropy, (unsigned int) (*bufstart), 1);

    bufstart++;

    nbits--;

  }

}

/*

 * Emit any pending EOBRUN symbol.

 */

LOCAL(void)

emit_eobrun (huff_entropy_ptr entropy)

{

  register int temp, nbits;

  if (entropy->EOBRUN > 0) {	/* if there is any pending EOBRUN */

    temp = entropy->EOBRUN;

    nbits = 0;

    while ((temp >>= 1))

      nbits++;

    /* safety check: shouldn't happen given limited correction-bit buffer */

    if (nbits > 14)

      ERREXIT(entropy->cinfo, JERR_HUFF_MISSING_CODE);

    emit_ac_symbol(entropy, entropy->ac_tbl_no, nbits << 4);

    if (nbits)

      emit_bits_e(entropy, entropy->EOBRUN, nbits);

    entropy->EOBRUN = 0;

    /* Emit any buffered correction bits */

    emit_buffered_bits(entropy, entropy->bit_buffer, entropy->BE);

    entropy->BE = 0;

  }

}

/*

 * Emit a restart marker & resynchronize predictions.

 */

LOCAL(boolean)

emit_restart_s (working_state * state, int restart_num)

{

  int ci;

  if (! flush_bits_s(state))

    return FALSE;

  emit_byte_s(state, 0xFF, return FALSE);

  emit_byte_s(state, JPEG_RST0 + restart_num, return FALSE);

  /* Re-initialize DC predictions to 0 */

  for (ci = 0; ci < state->cinfo->comps_in_scan; ci++)

    state->cur.last_dc_val[ci] = 0;

  /* The restart counter is not updated until we successfully write the MCU. */

  return TRUE;

}

LOCAL(void)

emit_restart_e (huff_entropy_ptr entropy, int restart_num)

{

  int ci;

  emit_eobrun(entropy);

  if (! entropy->gather_statistics) {

    flush_bits_e(entropy);

    emit_byte_e(entropy, 0xFF);

    emit_byte_e(entropy, JPEG_RST0 + restart_num);

  }

  if (entropy->cinfo->Ss == 0) {

    /* Re-initialize DC predictions to 0 */

    for (ci = 0; ci < entropy->cinfo->comps_in_scan; ci++)

      entropy->saved.last_dc_val[ci] = 0;

  } else {

    /* Re-initialize all AC-related fields to 0 */

    entropy->EOBRUN = 0;

    entropy->BE = 0;

  }

}

/*

 * MCU encoding for DC initial scan (either spectral selection,

 * or first pass of successive approximation).

 */

METHODDEF(boolean)

encode_mcu_DC_first (j_compress_ptr cinfo, JBLOCKROW *MCU_data)

{

  huff_entropy_ptr entropy = (huff_entropy_ptr) cinfo->entropy;

  register int temp, temp2;

  register int nbits;

  int blkn, ci;

  int Al = cinfo->Al;

  JBLOCKROW block;

  jpeg_component_info * compptr;

  ISHIFT_TEMPS

  entropy->next_output_byte = cinfo->dest->next_output_byte;

  entropy->free_in_buffer = cinfo->dest->free_in_buffer;

  /* Emit restart marker if needed */

  if (cinfo->restart_interval)

    if (entropy->restarts_to_go == 0)

      emit_restart_e(entropy, entropy->next_restart_num);

  /* Encode the MCU data blocks */

  for (blkn = 0; blkn < cinfo->blocks_in_MCU; blkn++) {

    block = MCU_data[blkn];

    ci = cinfo->MCU_membership[blkn];

    compptr = cinfo->cur_comp_info[ci];

    /* Compute the DC value after the required point transform by Al.

     * This is simply an arithmetic right shift.

     */

    temp2 = IRIGHT_SHIFT((int) ((*block)[0]), Al);

    /* DC differences are figured on the point-transformed values. */

    temp = temp2 - entropy->saved.last_dc_val[ci];

    entropy->saved.last_dc_val[ci] = temp2;

    /* Encode the DC coefficient difference per section G.1.2.1 */

    temp2 = temp;

    if (temp < 0) {

      temp = -temp;		/* temp is abs value of input */

      /* For a negative input, want temp2 = bitwise complement of abs(input) */

      /* This code assumes we are on a two's complement machine */

      temp2--;

    }

    /* Find the number of bits needed for the magnitude of the coefficient */

    nbits = 0;

    while (temp) {

      nbits++;

      temp >>= 1;

    }

    /* Check for out-of-range coefficient values.

     * Since we're encoding a difference, the range limit is twice as much.

     */

    if (nbits > MAX_COEF_BITS+1)

      ERREXIT(cinfo, JERR_BAD_DCT_COEF);

    /* Count/emit the Huffman-coded symbol for the number of bits */

    emit_dc_symbol(entropy, compptr->dc_tbl_no, nbits);

    /* Emit that number of bits of the value, if positive, */

    /* or the complement of its magnitude, if negative. */

    if (nbits)			/* emit_bits rejects calls with size 0 */

      emit_bits_e(entropy, (unsigned int) temp2, nbits);

  }

  cinfo->dest->next_output_byte = entropy->next_output_byte;

  cinfo->dest->free_in_buffer = entropy->free_in_buffer;

  /* Update restart-interval state too */

  if (cinfo->restart_interval) {

    if (entropy->restarts_to_go == 0) {

      entropy->restarts_to_go = cinfo->restart_interval;

      entropy->next_restart_num++;

      entropy->next_restart_num &= 7;

    }

    entropy->restarts_to_go--;

  }

  return TRUE;

}

/*

 * MCU encoding for AC initial scan (either spectral selection,

 * or first pass of successive approximation).

 */

METHODDEF(boolean)

encode_mcu_AC_first (j_compress_ptr cinfo, JBLOCKROW *MCU_data)

{

  huff_entropy_ptr entropy = (huff_entropy_ptr) cinfo->entropy;

  register int temp, temp2;

  register int nbits;

  register int r, k;

  int Se, Al;

  const int * natural_order;

  JBLOCKROW block;

  entropy->next_output_byte = cinfo->dest->next_output_byte;

  entropy->free_in_buffer = cinfo->dest->free_in_buffer;

  /* Emit restart marker if needed */

  if (cinfo->restart_interval)

    if (entropy->restarts_to_go == 0)

      emit_restart_e(entropy, entropy->next_restart_num);

  Se = cinfo->Se;

  Al = cinfo->Al;

  natural_order = cinfo->natural_order;

  /* Encode the MCU data block */

  block = MCU_data[0];

  /* Encode the AC coefficients per section G.1.2.2, fig. G.3 */

  r = 0;			/* r = run length of zeros */

  for (k = cinfo->Ss; k <= Se; k++) {

    if ((temp = (*block)[natural_order[k]]) == 0) {

      r++;

      continue;

    }

    /* We must apply the point transform by Al.  For AC coefficients this

     * is an integer division with rounding towards 0.  To do this portably

     * in C, we shift after obtaining the absolute value; so the code is

     * interwoven with finding the abs value (temp) and output bits (temp2).

     */

    if (temp < 0) {

      temp = -temp;		/* temp is abs value of input */

      temp >>= Al;		/* apply the point transform */

      /* For a negative coef, want temp2 = bitwise complement of abs(coef) */

      temp2 = ~temp;

    } else {

      temp >>= Al;		/* apply the point transform */

      temp2 = temp;

    }

    /* Watch out for case that nonzero coef is zero after point transform */

    if (temp == 0) {

      r++;

      continue;

    }

    /* Emit any pending EOBRUN */

    if (entropy->EOBRUN > 0)

      emit_eobrun(entropy);

    /* if run length > 15, must emit special run-length-16 codes (0xF0) */

    while (r > 15) {

      emit_ac_symbol(entropy, entropy->ac_tbl_no, 0xF0);

      r -= 16;

    }

    /* Find the number of bits needed for the magnitude of the coefficient */

    nbits = 1;			/* there must be at least one 1 bit */

    while ((temp >>= 1))

      nbits++;

    /* Check for out-of-range coefficient values */

    if (nbits > MAX_COEF_BITS)

      ERREXIT(cinfo, JERR_BAD_DCT_COEF);

    /* Count/emit Huffman symbol for run length / number of bits */

    emit_ac_symbol(entropy, entropy->ac_tbl_no, (r << 4) + nbits);

    /* Emit that number of bits of the value, if positive, */

    /* or the complement of its magnitude, if negative. */

    emit_bits_e(entropy, (unsigned int) temp2, nbits);

    r = 0;			/* reset zero run length */

  }

  if (r > 0) {			/* If there are trailing zeroes, */

    entropy->EOBRUN++;		/* count an EOB */

    if (entropy->EOBRUN == 0x7FFF)

      emit_eobrun(entropy);	/* force it out to avoid overflow */

  }

  cinfo->dest->next_output_byte = entropy->next_output_byte;

  cinfo->dest->free_in_buffer = entropy->free_in_buffer;

  /* Update restart-interval state too */

  if (cinfo->restart_interval) {

    if (entropy->restarts_to_go == 0) {

      entropy->restarts_to_go = cinfo->restart_interval;

      entropy->next_restart_num++;

      entropy->next_restart_num &= 7;

    }

    entropy->restarts_to_go--;

  }

  return TRUE;

}

/*

 * MCU encoding for DC successive approximation refinement scan.

 * Note: we assume such scans can be multi-component, although the spec

 * is not very clear on the point.

 */

METHODDEF(boolean)

encode_mcu_DC_refine (j_compress_ptr cinfo, JBLOCKROW *MCU_data)

{

  huff_entropy_ptr entropy = (huff_entropy_ptr) cinfo->entropy;

  register int temp;

  int blkn;

  int Al = cinfo->Al;

  JBLOCKROW block;

  entropy->next_output_byte = cinfo->dest->next_output_byte;

  entropy->free_in_buffer = cinfo->dest->free_in_buffer;

  /* Emit restart marker if needed */

  if (cinfo->restart_interval)

    if (entropy->restarts_to_go == 0)

      emit_restart_e(entropy, entropy->next_restart_num);

  /* Encode the MCU data blocks */

  for (blkn = 0; blkn < cinfo->blocks_in_MCU; blkn++) {

    block = MCU_data[blkn];

    /* We simply emit the Al'th bit of the DC coefficient value. */

    temp = (*block)[0];

    emit_bits_e(entropy, (unsigned int) (temp >> Al), 1);

  }

  cinfo->dest->next_output_byte = entropy->next_output_byte;

  cinfo->dest->free_in_buffer = entropy->free_in_buffer;

  /* Update restart-interval state too */

  if (cinfo->restart_interval) {

    if (entropy->restarts_to_go == 0) {

      entropy->restarts_to_go = cinfo->restart_interval;

      entropy->next_restart_num++;

      entropy->next_restart_num &= 7;

    }

    entropy->restarts_to_go--;

  }

  return TRUE;

}

/*

 * MCU encoding for AC successive approximation refinement scan.

 */

METHODDEF(boolean)

encode_mcu_AC_refine (j_compress_ptr cinfo, JBLOCKROW *MCU_data)

{

  huff_entropy_ptr entropy = (huff_entropy_ptr) cinfo->entropy;

  register int temp;

  register int r, k;

  int EOB;

  char *BR_buffer;

  unsigned int BR;

  int Se, Al;

  const int * natural_order;

  JBLOCKROW block;

  int absvalues[DCTSIZE2];

  entropy->next_output_byte = cinfo->dest->next_output_byte;

  entropy->free_in_buffer = cinfo->dest->free_in_buffer;

  /* Emit restart marker if needed */

  if (cinfo->restart_interval)

    if (entropy->restarts_to_go == 0)

      emit_restart_e(entropy, entropy->next_restart_num);

  Se = cinfo->Se;

  Al = cinfo->Al;

  natural_order = cinfo->natural_order;

  /* Encode the MCU data block */

  block = MCU_data[0];

  /* It is convenient to make a pre-pass to determine the transformed

   * coefficients' absolute values and the EOB position.

   */

  EOB = 0;

  for (k = cinfo->Ss; k <= Se; k++) {

    temp = (*block)[natural_order[k]];

    /* We must apply the point transform by Al.  For AC coefficients this

     * is an integer division with rounding towards 0.  To do this portably

     * in C, we shift after obtaining the absolute value.

     */

    if (temp < 0)

      temp = -temp;		/* temp is abs value of input */

    temp >>= Al;		/* apply the point transform */

    absvalues[k] = temp;	/* save abs value for main pass */

    if (temp == 1)

      EOB = k;			/* EOB = index of last newly-nonzero coef */

  }

  /* Encode the AC coefficients per section G.1.2.3, fig. G.7 */

  r = 0;			/* r = run length of zeros */

  BR = 0;			/* BR = count of buffered bits added now */

  BR_buffer = entropy->bit_buffer + entropy->BE; /* Append bits to buffer */

  for (k = cinfo->Ss; k <= Se; k++) {

    if ((temp = absvalues[k]) == 0) {

      r++;

      continue;

    }

    /* Emit any required ZRLs, but not if they can be folded into EOB */

    while (r > 15 && k <= EOB) {

      /* emit any pending EOBRUN and the BE correction bits */

      emit_eobrun(entropy);

      /* Emit ZRL */

      emit_ac_symbol(entropy, entropy->ac_tbl_no, 0xF0);

      r -= 16;

      /* Emit buffered correction bits that must be associated with ZRL */

      emit_buffered_bits(entropy, BR_buffer, BR);

      BR_buffer = entropy->bit_buffer; /* BE bits are gone now */

      BR = 0;

    }

    /* If the coef was previously nonzero, it only needs a correction bit.

     * NOTE: a straight translation of the spec's figure G.7 would suggest

     * that we also need to test r > 15.  But if r > 15, we can only get here

     * if k > EOB, which implies that this coefficient is not 1.

     */

    if (temp > 1) {

      /* The correction bit is the next bit of the absolute value. */

      BR_buffer[BR++] = (char) (temp & 1);

      continue;

    }

    /* Emit any pending EOBRUN and the BE correction bits */

    emit_eobrun(entropy);

    /* Count/emit Huffman symbol for run length / number of bits */

    emit_ac_symbol(entropy, entropy->ac_tbl_no, (r << 4) + 1);

    /* Emit output bit for newly-nonzero coef */

    temp = ((*block)[natural_order[k]] < 0) ? 0 : 1;

    emit_bits_e(entropy, (unsigned int) temp, 1);

    /* Emit buffered correction bits that must be associated with this code */