/*

 * jchuff.c

 *

 * This file was part of the Independent JPEG Group's software:

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

 * libjpeg-turbo Modifications:

 * Copyright (C) 2009-2011, 2014-2016, 2018-2019, 2021, D. R. Commander.

 * Copyright (C) 2015, Matthieu Darbois.

 * For conditions of distribution and use, see the accompanying README.ijg

 * file.

 *

 * This file contains Huffman entropy encoding routines.

 *

 * 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.

 *

 * NOTE: All referenced figures are from

 * Recommendation ITU-T T.81 (1992) | ISO/IEC 10918-1:1994.

 */

#define JPEG_INTERNALS

#include "jinclude.h"

#include "jpeglib.h"

#include "jsimd.h"

#include "jconfigint.h"

#include <limits.h>

/*

 * NOTE: If USE_CLZ_INTRINSIC is defined, then clz/bsr instructions will be

 * used for bit counting rather than the lookup table.  This will reduce the

 * memory footprint by 64k, which is important for some mobile applications

 * that create many isolated instances of libjpeg-turbo (web browsers, for

 * instance.)  This may improve performance on some mobile platforms as well.

 * This feature is enabled by default only on Arm processors, because some x86

 * chips have a slow implementation of bsr, and the use of clz/bsr cannot be

 * shown to have a significant performance impact even on the x86 chips that

 * have a fast implementation of it.  When building for Armv6, you can

 * explicitly disable the use of clz/bsr by adding -mthumb to the compiler

 * flags (this defines __thumb__).

 */

/* NOTE: Both GCC and Clang define __GNUC__ */

#if defined(__GNUC__) && (defined(__arm__) || defined(__aarch64__))

#if !defined(__thumb__) || defined(__thumb2__)

#define USE_CLZ_INTRINSIC

#endif

#endif

#ifdef USE_CLZ_INTRINSIC

#define JPEG_NBITS_NONZERO(x)  (32 - __builtin_clz(x))

#define JPEG_NBITS(x)          (x ? JPEG_NBITS_NONZERO(x) : 0)

#else

#include "jpeg_nbits_table.h"

#define JPEG_NBITS(x)          (jpeg_nbits_table[x])

#define JPEG_NBITS_NONZERO(x)  JPEG_NBITS(x)

#endif

/* 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 {

  size_t 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];

#ifdef ENTROPY_OPT_SUPPORTED    /* Statistics tables for optimization */

  long *dc_count_ptrs[NUM_HUFF_TBLS];

  long *ac_count_ptrs[NUM_HUFF_TBLS];

#endif

  int simd;

} huff_entropy_encoder;

typedef huff_entropy_encoder *huff_entropy_ptr;

/* Working state while writing an MCU.

 * 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;

/* Forward declarations */

METHODDEF(boolean) encode_mcu_huff(j_compress_ptr cinfo, JBLOCKROW *MCU_data);

METHODDEF(void) finish_pass_huff(j_compress_ptr cinfo);

#ifdef ENTROPY_OPT_SUPPORTED

METHODDEF(boolean) encode_mcu_gather(j_compress_ptr cinfo,

                                     JBLOCKROW *MCU_data);

METHODDEF(void) finish_pass_gather(j_compress_ptr cinfo);

#endif

/*

 * Initialize for a Huffman-compressed scan.

 * If gather_statistics is TRUE, we do not output anything during the scan,

 * just count the Huffman symbols used and generate Huffman code tables.

 */

METHODDEF(void)

start_pass_huff(j_compress_ptr cinfo, boolean gather_statistics)

{

  huff_entropy_ptr entropy = (huff_entropy_ptr)cinfo->entropy;

  int ci, dctbl, actbl;

  jpeg_component_info *compptr;

  if (gather_statistics) {

#ifdef ENTROPY_OPT_SUPPORTED

    entropy->pub.encode_mcu = encode_mcu_gather;

    entropy->pub.finish_pass = finish_pass_gather;

#else

    ERREXIT(cinfo, JERR_NOT_COMPILED);

#endif

  } else {

    entropy->pub.encode_mcu = encode_mcu_huff;

    entropy->pub.finish_pass = finish_pass_huff;

  }

  entropy->simd = jsimd_can_huff_encode_one_block();

  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;

    if (gather_statistics) {

#ifdef ENTROPY_OPT_SUPPORTED

      /* Check for invalid table indexes */

      /* (make_c_derived_tbl does this in the other path) */

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

        ERREXIT1(cinfo, JERR_NO_HUFF_TABLE, dctbl);

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

        ERREXIT1(cinfo, JERR_NO_HUFF_TABLE, actbl);

      /* Allocate and zero the statistics tables */

      /* Note that jpeg_gen_optimal_table expects 257 entries in each table! */

      if (entropy->dc_count_ptrs[dctbl] == NULL)

        entropy->dc_count_ptrs[dctbl] = (long *)

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

                                      257 * sizeof(long));

      MEMZERO(entropy->dc_count_ptrs[dctbl], 257 * sizeof(long));

      if (entropy->ac_count_ptrs[actbl] == NULL)

        entropy->ac_count_ptrs[actbl] = (long *)

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

                                      257 * sizeof(long));

      MEMZERO(entropy->ac_count_ptrs[actbl], 257 * sizeof(long));

#endif

    } else {

      /* Compute derived values for Huffman tables */

      /* We may do this more than once for a table, but it's not expensive */

      jpeg_make_c_derived_tbl(cinfo, TRUE, dctbl,

                              &entropy->dc_derived_tbls[dctbl]);

      jpeg_make_c_derived_tbl(cinfo, FALSE, actbl,

                              &entropy->ac_derived_tbls[actbl]);

    }

    /* Initialize DC predictions to 0 */

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

  }

  /* Initialize bit buffer to empty */

  entropy->saved.put_buffer = 0;

  entropy->saved.put_bits = 0;

  /* Initialize restart stuff */

  entropy->restarts_to_go = cinfo->restart_interval;

  entropy->next_restart_num = 0;

}

/*

 * Compute the derived values for a Huffman table.

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

 *

 * Note this is also used by jcphuff.c.

 */

GLOBAL(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 (((JLONG)code) >= (((JLONG)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->ehufco, sizeof(dtbl->ehufco));

  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 */

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

#define emit_byte(state, val, action) { \

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

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

    if (!dump_buffer(state)) \

      { action; } \

}

LOCAL(boolean)

dump_buffer(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;

}

/* Outputting bits to the file */

/* These macros perform the same task as the emit_bits() function in the

 * original libjpeg code.  In addition to reducing overhead by explicitly

 * inlining the code, additional performance is achieved by taking into

 * account the size of the bit buffer and waiting until it is almost full

 * before emptying it.  This mostly benefits 64-bit platforms, since 6

 * bytes can be stored in a 64-bit bit buffer before it has to be emptied.

 */

#define EMIT_BYTE() { \

  JOCTET c; \

  put_bits -= 8; \

  c = (JOCTET)GETJOCTET(put_buffer >> put_bits); \

  *buffer++ = c; \

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

    *buffer++ = 0; \

}

#define PUT_BITS(code, size) { \

  put_bits += size; \

  put_buffer = (put_buffer << size) | code; \

}

#if SIZEOF_SIZE_T != 8 && !defined(_WIN64)

#define CHECKBUF15() { \

  if (put_bits > 15) { \

    EMIT_BYTE() \

    EMIT_BYTE() \

  } \

}

#endif

#define CHECKBUF31() { \

  if (put_bits > 31) { \

    EMIT_BYTE() \

    EMIT_BYTE() \

    EMIT_BYTE() \

    EMIT_BYTE() \

  } \

}

#define CHECKBUF47() { \

  if (put_bits > 47) { \

    EMIT_BYTE() \

    EMIT_BYTE() \

    EMIT_BYTE() \

    EMIT_BYTE() \

    EMIT_BYTE() \

    EMIT_BYTE() \

  } \

}

#if !defined(_WIN32) && !defined(SIZEOF_SIZE_T)

#error Cannot determine word size

#endif

#if SIZEOF_SIZE_T == 8 || defined(_WIN64)

#define EMIT_BITS(code, size) { \

  CHECKBUF47() \

  PUT_BITS(code, size) \

}

#define EMIT_CODE(code, size) { \

  temp2 &= (((JLONG)1) << nbits) - 1; \

  CHECKBUF31() \

  PUT_BITS(code, size) \

  PUT_BITS(temp2, nbits) \

}

#else

#define EMIT_BITS(code, size) { \

  PUT_BITS(code, size) \

  CHECKBUF15() \

}

#define EMIT_CODE(code, size) { \

  temp2 &= (((JLONG)1) << nbits) - 1; \

  PUT_BITS(code, size) \

  CHECKBUF15() \

  PUT_BITS(temp2, nbits) \

  CHECKBUF15() \

}

#endif

/* Although it is exceedingly rare, it is possible for a Huffman-encoded

 * coefficient block to be larger than the 128-byte unencoded block.  For each

 * of the 64 coefficients, PUT_BITS is invoked twice, and each invocation can

 * theoretically store 16 bits (for a maximum of 2048 bits or 256 bytes per

 * encoded block.)  If, for instance, one artificially sets the AC

 * coefficients to alternating values of 32767 and -32768 (using the JPEG

 * scanning order-- 1, 8, 16, etc.), then this will produce an encoded block

 * larger than 200 bytes.

 */

#define BUFSIZE  (DCTSIZE2 * 8)

#define LOAD_BUFFER() { \

  if (state->free_in_buffer < BUFSIZE) { \

    localbuf = 1; \

    buffer = _buffer; \

  } else \

    buffer = state->next_output_byte; \

}

#define STORE_BUFFER() { \

  if (localbuf) { \

    bytes = buffer - _buffer; \

    buffer = _buffer; \

    while (bytes > 0) { \

      bytestocopy = MIN(bytes, state->free_in_buffer); \

      MEMCOPY(state->next_output_byte, buffer, bytestocopy); \

      state->next_output_byte += bytestocopy; \

      buffer += bytestocopy; \

      state->free_in_buffer -= bytestocopy; \

      if (state->free_in_buffer == 0) \

        if (!dump_buffer(state)) return FALSE; \

      bytes -= bytestocopy; \

    } \

  } else { \

    state->free_in_buffer -= (buffer - state->next_output_byte); \

    state->next_output_byte = buffer; \

  } \

}

LOCAL(boolean)

flush_bits(working_state *state)

{

  JOCTET _buffer[BUFSIZE], *buffer;

  size_t put_buffer;  int put_bits;

  size_t bytes, bytestocopy;  int localbuf = 0;

  put_buffer = state->cur.put_buffer;

  put_bits = state->cur.put_bits;

  LOAD_BUFFER()

  /* fill any partial byte with ones */

  PUT_BITS(0x7F, 7)

  while (put_bits >= 8) EMIT_BYTE()

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

  state->cur.put_bits = 0;

  STORE_BUFFER()

  return TRUE;

}

/* Encode a single block's worth of coefficients */

LOCAL(boolean)

encode_one_block_simd(working_state *state, JCOEFPTR block, int last_dc_val,

                      c_derived_tbl *dctbl, c_derived_tbl *actbl)

{

  JOCTET _buffer[BUFSIZE], *buffer;

  size_t bytes, bytestocopy;  int localbuf = 0;

  LOAD_BUFFER()

  buffer = jsimd_huff_encode_one_block(state, buffer, block, last_dc_val,

                                       dctbl, actbl);

  STORE_BUFFER()

  return TRUE;

}

LOCAL(boolean)

encode_one_block(working_state *state, JCOEFPTR block, int last_dc_val,

                 c_derived_tbl *dctbl, c_derived_tbl *actbl)

{

  int temp, temp2, temp3;

  int nbits;

  int r, code, size;

  JOCTET _buffer[BUFSIZE], *buffer;

  size_t put_buffer;  int put_bits;

  int code_0xf0 = actbl->ehufco[0xf0], size_0xf0 = actbl->ehufsi[0xf0];

  size_t bytes, bytestocopy;  int localbuf = 0;

  put_buffer = state->cur.put_buffer;

  put_bits = state->cur.put_bits;

  LOAD_BUFFER()

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

  temp = temp2 = block[0] - last_dc_val;

  /* This is a well-known technique for obtaining the absolute value without a

   * branch.  It is derived from an assembly language technique presented in

   * "How to Optimize for the Pentium Processors", Copyright (c) 1996, 1997 by

   * Agner Fog.

   */

  temp3 = temp >> (CHAR_BIT * sizeof(int) - 1);

  temp ^= temp3;

  temp -= temp3;

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

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

  temp2 += temp3;

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

  nbits = JPEG_NBITS(temp);

  /* Emit the Huffman-coded symbol for the number of bits */

  code = dctbl->ehufco[nbits];

  size = dctbl->ehufsi[nbits];

  EMIT_BITS(code, size)

  /* Mask off any extra bits in code */

  temp2 &= (((JLONG)1) << nbits) - 1;

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

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

  EMIT_BITS(temp2, nbits)

  /* Encode the AC coefficients per section F.1.2.2 */

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

/* Manually unroll the k loop to eliminate the counter variable.  This

 * improves performance greatly on systems with a limited number of

 * registers (such as x86.)

 */

#define kloop(jpeg_natural_order_of_k) { \

  if ((temp = block[jpeg_natural_order_of_k]) == 0) { \

    r++; \

  } else { \

    temp2 = temp; \

    /* Branch-less absolute value, bitwise complement, etc., same as above */ \

    temp3 = temp >> (CHAR_BIT * sizeof(int) - 1); \

    temp ^= temp3; \

    temp -= temp3; \

    temp2 += temp3; \

    nbits = JPEG_NBITS_NONZERO(temp); \

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

    while (r > 15) { \

      EMIT_BITS(code_0xf0, size_0xf0) \

      r -= 16; \

    } \

    /* Emit Huffman symbol for run length / number of bits */ \

    temp3 = (r << 4) + nbits; \

    code = actbl->ehufco[temp3]; \

    size = actbl->ehufsi[temp3]; \

    EMIT_CODE(code, size) \

    r = 0; \

  } \

}

  /* One iteration for each value in jpeg_natural_order[] */

  kloop(1);   kloop(8);   kloop(16);  kloop(9);   kloop(2);   kloop(3);

  kloop(10);  kloop(17);  kloop(24);  kloop(32);  kloop(25);  kloop(18);

  kloop(11);  kloop(4);   kloop(5);   kloop(12);  kloop(19);  kloop(26);

  kloop(33);  kloop(40);  kloop(48);  kloop(41);  kloop(34);  kloop(27);

  kloop(20);  kloop(13);  kloop(6);   kloop(7);   kloop(14);  kloop(21);

  kloop(28);  kloop(35);  kloop(42);  kloop(49);  kloop(56);  kloop(57);

  kloop(50);  kloop(43);  kloop(36);  kloop(29);  kloop(22);  kloop(15);

  kloop(23);  kloop(30);  kloop(37);  kloop(44);  kloop(51);  kloop(58);

  kloop(59);  kloop(52);  kloop(45);  kloop(38);  kloop(31);  kloop(39);

  kloop(46);  kloop(53);  kloop(60);  kloop(61);  kloop(54);  kloop(47);

  kloop(55);  kloop(62);  kloop(63);

  /* If the last coef(s) were zero, emit an end-of-block code */

  if (r > 0) {

    code = actbl->ehufco[0];

    size = actbl->ehufsi[0];

    EMIT_BITS(code, size)

  }

  state->cur.put_buffer = put_buffer;

  state->cur.put_bits = put_bits;

  STORE_BUFFER()

  return TRUE;

}

/*

 * Emit a restart marker & resynchronize predictions.

 */

LOCAL(boolean)

emit_restart(working_state *state, int restart_num)

{

  int ci;

  if (!flush_bits(state))

    return FALSE;

  emit_byte(state, 0xFF, return FALSE);

  emit_byte(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;

}

/*

 * Encode and output one MCU's worth of Huffman-compressed coefficients.

 */

METHODDEF(boolean)

encode_mcu_huff(j_compress_ptr cinfo, JBLOCKROW *MCU_data)

{

  huff_entropy_ptr entropy = (huff_entropy_ptr)cinfo->entropy;

  working_state state;

  int blkn, ci;

  jpeg_component_info *compptr;

  /* Load up working state */

  state.next_output_byte = cinfo->dest->next_output_byte;

  state.free_in_buffer = cinfo->dest->free_in_buffer;

  ASSIGN_STATE(state.cur, entropy->saved);

  state.cinfo = cinfo;

  /* Emit restart marker if needed */

  if (cinfo->restart_interval) {

    if (entropy->restarts_to_go == 0)

      if (!emit_restart(&state, entropy->next_restart_num))

        return FALSE;

  }

  /* Encode the MCU data blocks */

  if (entropy->simd) {

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

      ci = cinfo->MCU_membership[blkn];

      compptr = cinfo->cur_comp_info[ci];

      if (!encode_one_block_simd(&state,

                                 MCU_data[blkn][0], state.cur.last_dc_val[ci],

                                 entropy->dc_derived_tbls[compptr->dc_tbl_no],

                                 entropy->ac_derived_tbls[compptr->ac_tbl_no]))

        return FALSE;

      /* Update last_dc_val */

      state.cur.last_dc_val[ci] = MCU_data[blkn][0][0];

    }

  } else {

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

      ci = cinfo->MCU_membership[blkn];

      compptr = cinfo->cur_comp_info[ci];

      if (!encode_one_block(&state,

                            MCU_data[blkn][0], state.cur.last_dc_val[ci],

                            entropy->dc_derived_tbls[compptr->dc_tbl_no],

                            entropy->ac_derived_tbls[compptr->ac_tbl_no]))

        return FALSE;

      /* Update last_dc_val */

      state.cur.last_dc_val[ci] = MCU_data[blkn][0][0];

    }

  }

  /* Completed MCU, so update state */

  cinfo->dest->next_output_byte = state.next_output_byte;

  cinfo->dest->free_in_buffer = state.free_in_buffer;

  ASSIGN_STATE(entropy->saved, state.cur);

  /* 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;

}

/*

 * Finish up at the end of a Huffman-compressed scan.

 */

METHODDEF(void)

finish_pass_huff(j_compress_ptr cinfo)

{

  huff_entropy_ptr entropy = (huff_entropy_ptr)cinfo->entropy;

  working_state state;

  /* Load up working state ... flush_bits needs it */

  state.next_output_byte = cinfo->dest->next_output_byte;

  state.free_in_buffer = cinfo->dest->free_in_buffer;

  ASSIGN_STATE(state.cur, entropy->saved);

  state.cinfo = cinfo;

  /* Flush out the last data */

  if (!flush_bits(&state))

    ERREXIT(cinfo, JERR_CANT_SUSPEND);

  /* Update state */

  cinfo->dest->next_output_byte = state.next_output_byte;

  cinfo->dest->free_in_buffer = state.free_in_buffer;

  ASSIGN_STATE(entropy->saved, state.cur);

}

/*

 * Huffman coding optimization.

 *

 * We first scan the supplied data and count the number of uses of each symbol

 * that is to be Huffman-coded. (This process MUST agree with the code above.)

 * Then we build a Huffman coding tree for the observed counts.

 * Symbols which are not needed at all for the particular image are not

 * assigned any code, which saves space in the DHT marker as well as in

 * the compressed data.

 */

#ifdef ENTROPY_OPT_SUPPORTED

/* Process a single block's worth of coefficients */

LOCAL(void)

htest_one_block(j_compress_ptr cinfo, JCOEFPTR block, int last_dc_val,

                long dc_counts[], long ac_counts[])

{

  register int temp;

  register int nbits;

  register int k, r;

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

  temp = block[0] - last_dc_val;

  if (temp < 0)

    temp = -temp;

  /* 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 the Huffman symbol for the number of bits */

  dc_counts[nbits]++;

  /* Encode the AC coefficients per section F.1.2.2 */

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

  for (k = 1; k < DCTSIZE2; k++) {

    if ((temp = block[jpeg_natural_order[k]]) == 0) {

      r++;

    } else {

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

      while (r > 15) {

        ac_counts[0xF0]++;

        r -= 16;

      }

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

      if (temp < 0)

        temp = -temp;

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

      ac_counts[(r << 4) + nbits]++;

      r = 0;

    }

  }

  /* If the last coef(s) were zero, emit an end-of-block code */

  if (r > 0)

    ac_counts[0]++;

}

/*

 * Trial-encode one MCU's worth of Huffman-compressed coefficients.

 * No data is actually output, so no suspension return is possible.

 */

METHODDEF(boolean)

encode_mcu_gather(j_compress_ptr cinfo, JBLOCKROW *MCU_data)

{

  huff_entropy_ptr entropy = (huff_entropy_ptr)cinfo->entropy;

  int blkn, ci;

  jpeg_component_info *compptr;

  /* Take care of restart intervals if needed */

  if (cinfo->restart_interval) {

    if (entropy->restarts_to_go == 0) {

      /* Re-initialize DC predictions to 0 */

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

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

      /* Update restart state */

      entropy->restarts_to_go = cinfo->restart_interval;

    }

    entropy->restarts_to_go--;

  }

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

    ci = cinfo->MCU_membership[blkn];

    compptr = cinfo->cur_comp_info[ci];

    htest_one_block(cinfo, MCU_data[blkn][0], entropy->saved.last_dc_val[ci],

                    entropy->dc_count_ptrs[compptr->dc_tbl_no],

                    entropy->ac_count_ptrs[compptr->ac_tbl_no]);

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

  }

  return TRUE;

}

/*

 * Generate the best Huffman code table for the given counts, fill htbl.

 * Note this is also used by jcphuff.c.

 *

 * The JPEG standard requires that no symbol be assigned a codeword of all

 * one bits (so that padding bits added at the end of a compressed segment

 * can't look like a valid code).  Because of the canonical ordering of

 * codewords, this just means that there must be an unused slot in the

 * longest codeword length category.  Annex K (Clause K.2) of

 * Rec. ITU-T T.81 (1992) | ISO/IEC 10918-1:1994 suggests reserving such a slot

 * by pretending that symbol 256 is a valid symbol with count 1.  In theory

 * that's not optimal; giving it count zero but including it in the symbol set

 * anyway should give a better Huffman code.  But the theoretically better code

 * actually seems to come out worse in practice, because it produces more

 * all-ones bytes (which incur stuffed zero bytes in the final file).  In any

 * case the difference is tiny.

 *

 * The JPEG standard requires Huffman codes to be no more than 16 bits long.

 * If some symbols have a very small but nonzero probability, the Huffman tree

 * must be adjusted to meet the code length restriction.  We currently use

 * the adjustment method suggested in JPEG section K.2.  This method is *not*

 * optimal; it may not choose the best possible limited-length code.  But

 * typically only very-low-frequency symbols will be given less-than-optimal

 * lengths, so the code is almost optimal.  Experimental comparisons against

 * an optimal limited-length-code algorithm indicate that the difference is

 * microscopic --- usually less than a hundredth of a percent of total size.

 * So the extra complexity of an optimal algorithm doesn't seem worthwhile.

 */

GLOBAL(void)

jpeg_gen_optimal_table(j_compress_ptr cinfo, JHUFF_TBL *htbl, long freq[])

{

#define MAX_CLEN  32            /* assumed maximum initial code length */

  UINT8 bits[MAX_CLEN + 1];     /* bits[k] = # of symbols with code length k */

  int codesize[257];            /* codesize[k] = code length of symbol k */

  int others[257];              /* next symbol in current branch of tree */

  int c1, c2;

  int p, i, j;

  long v;

  /* This algorithm is explained in section K.2 of the JPEG standard */

  MEMZERO(bits, sizeof(bits));

  MEMZERO(codesize, sizeof(codesize));

  for (i = 0; i < 257; i++)

    others[i] = -1;             /* init links to empty */

  freq[256] = 1;                /* make sure 256 has a nonzero count */

  /* Including the pseudo-symbol 256 in the Huffman procedure guarantees

   * that no real symbol is given code-value of all ones, because 256

   * will be placed last in the largest codeword category.

   */

  /* Huffman's basic algorithm to assign optimal code lengths to symbols */

  for (;;) {

    /* Find the smallest nonzero frequency, set c1 = its symbol */

    /* In case of ties, take the larger symbol number */

    c1 = -1;

    v = 1000000000L;

    for (i = 0; i <= 256; i++) {

      if (freq[i] && freq[i] <= v) {

        v = freq[i];

        c1 = i;

      }

    }

    /* Find the next smallest nonzero frequency, set c2 = its symbol */

    /* In case of ties, take the larger symbol number */

    c2 = -1;

    v = 1000000000L;

    for (i = 0; i <= 256; i++) {

      if (freq[i] && freq[i] <= v && i != c1) {

        v = freq[i];

        c2 = i;

      }

    }

    /* Done if we've merged everything into one frequency */

    if (c2 < 0)

      break;

    /* Else merge the two counts/trees */

    freq[c1] += freq[c2];

    freq[c2] = 0;

    /* Increment the codesize of everything in c1's tree branch */

    codesize[c1]++;

    while (others[c1] >= 0) {

      c1 = others[c1];

      codesize[c1]++;

    }

    others[c1] = c2;            /* chain c2 onto c1's tree branch */

    /* Increment the codesize of everything in c2's tree branch */

    codesize[c2]++;

    while (others[c2] >= 0) {

      c2 = others[c2];

      codesize[c2]++;

    }

  }

  /* Now count the number of symbols of each code length */

  for (i = 0; i <= 256; i++) {

    if (codesize[i]) {

      /* The JPEG standard seems to think that this can't happen, */

      /* but I'm paranoid... */

      if (codesize[i] > MAX_CLEN)

        ERREXIT(cinfo, JERR_HUFF_CLEN_OVERFLOW);

      bits[codesize[i]]++;

    }

  }

  /* JPEG doesn't allow symbols with code lengths over 16 bits, so if the pure

   * Huffman procedure assigned any such lengths, we must adjust the coding.

   * Here is what Rec. ITU-T T.81 | ISO/IEC 10918-1 says about how this next

   * bit works: Since symbols are paired for the longest Huffman code, the

   * symbols are removed from this length category two at a time.  The prefix

   * for the pair (which is one bit shorter) is allocated to one of the pair;

   * then, skipping the BITS entry for that prefix length, a code word from the

   * next shortest nonzero BITS entry is converted into a prefix for two code

   * words one bit longer.

   */

  for (i = MAX_CLEN; i > 16; i--) {

    while (bits[i] > 0) {

      j = i - 2;                /* find length of new prefix to be used */

      while (bits[j] == 0)

        j--;

      bits[i] -= 2;             /* remove two symbols */

      bits[i - 1]++;            /* one goes in this length */

      bits[j + 1] += 2;         /* two new symbols in this length */

      bits[j]--;                /* symbol of this length is now a prefix */

    }

  }

  /* Remove the count for the pseudo-symbol 256 from the largest codelength */

  while (bits[i] == 0)          /* find largest codelength still in use */

    i--;

  bits[i]--;

  /* Return final symbol counts (only for lengths 0..16) */

  MEMCOPY(htbl->bits, bits, sizeof(htbl->bits));

  /* Return a list of the symbols sorted by code length */

  /* It's not real clear to me why we don't need to consider the codelength

   * changes made above, but Rec. ITU-T T.81 | ISO/IEC 10918-1 seems to think

   * this works.

   */

  p = 0;

  for (i = 1; i <= MAX_CLEN; i++) {

    for (j = 0; j <= 255; j++) {

      if (codesize[j] == i) {

        htbl->huffval[p] = (UINT8)j;

        p++;

      }

    }