/*

 * jclhuff.c

 *

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

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

 * Lossless JPEG Modifications:

 * Copyright (C) 1999, Ken Murchison.

 * libjpeg-turbo Modifications:

 * Copyright (C) 2022, 2026, D. R. Commander.

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

 * file.

 *

 * This file contains Huffman entropy encoding routines for lossless JPEG.

 *

 * 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.

 */

#define JPEG_INTERNALS

#include "jinclude.h"

#include "jpeglib.h"

#include "jlossls.h"            /* Private declarations for lossless codec */

#include "jchuff.h"             /* Declarations shared with jc*huff.c */

#ifdef C_LOSSLESS_SUPPORTED

/* The legal range of a spatial difference is

 * -32767 .. +32768.

 * Hence the magnitude should always fit in 16 bits.

 */

#define MAX_DIFF_BITS  16

/* Expanded entropy encoder object for Huffman encoding in lossless mode.

 *

 * 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 */

} savable_state;

typedef struct {

  int ci, yoffset, MCU_width;

} lhe_input_ptr_info;

typedef struct {

  struct jpeg_entropy_encoder pub; /* public fields */

  savable_state saved;          /* Bit buffer 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 *derived_tbls[NUM_HUFF_TBLS];

  /* Pointers to derived tables to be used for each data unit within an MCU */

  c_derived_tbl *cur_tbls[C_MAX_BLOCKS_IN_MCU];

#ifdef ENTROPY_OPT_SUPPORTED    /* Statistics tables for optimization */

  long *count_ptrs[NUM_HUFF_TBLS];

  /* Pointers to stats tables to be used for each data unit within an MCU */

  long *cur_counts[C_MAX_BLOCKS_IN_MCU];

#endif

  /* Pointers to the proper input difference row for each group of data units

   * within an MCU.  For each component, there are Vi groups of Hi data units.

   */

  JDIFFROW input_ptr[C_MAX_BLOCKS_IN_MCU];

  /* Number of input pointers in use for the current MCU.  This is the sum

   * of all Vi in the MCU.

   */

  int num_input_ptrs;

  /* Information used for positioning the input pointers within the input

   * difference rows.

   */

  lhe_input_ptr_info input_ptr_info[C_MAX_BLOCKS_IN_MCU];

  /* Index of the proper input pointer for each data unit within an MCU */

  int input_ptr_index[C_MAX_BLOCKS_IN_MCU];

} lhuff_entropy_encoder;

typedef lhuff_entropy_encoder *lhuff_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(JDIMENSION) encode_mcus_huff(j_compress_ptr cinfo,

                                       JDIFFIMAGE diff_buf,

                                       JDIMENSION MCU_row_num,

                                       JDIMENSION MCU_col_num,

                                       JDIMENSION nMCU);

METHODDEF(void) finish_pass_huff(j_compress_ptr cinfo);

#ifdef ENTROPY_OPT_SUPPORTED

METHODDEF(JDIMENSION) encode_mcus_gather(j_compress_ptr cinfo,

                                         JDIFFIMAGE diff_buf,

                                         JDIMENSION MCU_row_num,

                                         JDIMENSION MCU_col_num,

                                         JDIMENSION nMCU);

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_lhuff(j_compress_ptr cinfo, boolean gather_statistics)

{

  lhuff_entropy_ptr entropy = (lhuff_entropy_ptr)cinfo->entropy;

  int ci, dctbl, sampn, ptrn, yoffset, xoffset;

  jpeg_component_info *compptr;

  if (gather_statistics) {

#ifdef ENTROPY_OPT_SUPPORTED

    entropy->pub.encode_mcus = encode_mcus_gather;

    entropy->pub.finish_pass = finish_pass_gather;

#else

    ERREXIT(cinfo, JERR_NOT_COMPILED);

#endif

  } else {

    entropy->pub.encode_mcus = encode_mcus_huff;

    entropy->pub.finish_pass = finish_pass_huff;

  }

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

    compptr = cinfo->cur_comp_info[ci];

    dctbl = compptr->dc_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);

      /* Allocate and zero the statistics tables */

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

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

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

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

                                      257 * sizeof(long));

      memset(entropy->count_ptrs[dctbl], 0, 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->derived_tbls[dctbl]);

    }

  }

  /* Precalculate encoding info for each sample in an MCU of this scan */

  for (sampn = 0, ptrn = 0; sampn < cinfo->blocks_in_MCU;) {

    compptr = cinfo->cur_comp_info[cinfo->MCU_membership[sampn]];

    ci = compptr->component_index;

    for (yoffset = 0; yoffset < compptr->MCU_height; yoffset++, ptrn++) {

      /* Precalculate the setup info for each input pointer */

      entropy->input_ptr_info[ptrn].ci = ci;

      entropy->input_ptr_info[ptrn].yoffset = yoffset;

      entropy->input_ptr_info[ptrn].MCU_width = compptr->MCU_width;

      for (xoffset = 0; xoffset < compptr->MCU_width; xoffset++, sampn++) {

        /* Precalculate the input pointer index for each sample */

        entropy->input_ptr_index[sampn] = ptrn;

        /* Precalculate which tables to use for each sample */

        entropy->cur_tbls[sampn] = entropy->derived_tbls[compptr->dc_tbl_no];

#ifdef ENTROPY_OPT_SUPPORTED

        entropy->cur_counts[sampn] = entropy->count_ptrs[compptr->dc_tbl_no];

#endif

      }

    }

  }

  entropy->num_input_ptrs = ptrn;

  /* 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;

}

/* 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 */

/* 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(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 size_t put_buffer = (size_t)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 &= (((size_t)1) << size) - 1; /* mask off any extra bits in code */

  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(state, c, return FALSE);

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

      emit_byte(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;

}

LOCAL(boolean)

flush_bits(working_state *state)

{

  if (!emit_bits(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;

}

/*

 * Emit a restart marker & resynchronize predictions.

 */

LOCAL(boolean)

emit_restart(working_state *state, int restart_num)

{

  if (!flush_bits(state))

    return FALSE;

  emit_byte(state, 0xFF, return FALSE);

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

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

  return TRUE;

}

/*

 * Encode and output nMCU MCUs' worth of Huffman-compressed differences.

 */

METHODDEF(JDIMENSION)

encode_mcus_huff(j_compress_ptr cinfo, JDIFFIMAGE diff_buf,

                 JDIMENSION MCU_row_num, JDIMENSION MCU_col_num,

                 JDIMENSION nMCU)

{

  lhuff_entropy_ptr entropy = (lhuff_entropy_ptr)cinfo->entropy;

  working_state state;

  int sampn, ci, yoffset, MCU_width, ptrn;

  JDIMENSION mcu_num;

  /* Load up working state */

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

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

  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 0;

  }

  /* Set input pointer locations based on MCU_col_num */

  for (ptrn = 0; ptrn < entropy->num_input_ptrs; ptrn++) {

    ci = entropy->input_ptr_info[ptrn].ci;

    yoffset = entropy->input_ptr_info[ptrn].yoffset;

    MCU_width = entropy->input_ptr_info[ptrn].MCU_width;

    entropy->input_ptr[ptrn] =

      diff_buf[ci][MCU_row_num + yoffset] + (MCU_col_num * MCU_width);

  }

  for (mcu_num = 0; mcu_num < nMCU; mcu_num++) {

    /* Inner loop handles the samples in the MCU */

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

      register int temp, temp2;

      register int nbits;

      c_derived_tbl *dctbl = entropy->cur_tbls[sampn];

      /* Encode the difference per section H.1.2.2 */

      /* Input the sample difference */

      temp = *entropy->input_ptr[entropy->input_ptr_index[sampn]]++;

      if (temp & 0x8000) {      /* instead of temp < 0 */

        temp = (-temp) & 0x7FFF; /* absolute value, mod 2^16 */

        if (temp == 0)          /* special case: magnitude = 32768 */

          temp2 = temp = 0x8000;

        temp2 = ~temp;          /* one's complement of magnitude */

      } else {

        temp &= 0x7FFF;         /* abs value mod 2^16 */

        temp2 = temp;           /* magnitude */

      }

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

      nbits = 0;

      while (temp) {

        nbits++;

        temp >>= 1;

      }

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

       */

      if (nbits > MAX_DIFF_BITS)

        ERREXIT(cinfo, JERR_BAD_DCT_COEF);

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

      if (!emit_bits(&state, dctbl->ehufco[nbits], dctbl->ehufsi[nbits]))

        return mcu_num;

      /* 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 */

          nbits != 16)          /* special case: no bits should be emitted */

        if (!emit_bits(&state, (unsigned int)temp2, nbits))

          return mcu_num;

    }

    /* Completed MCU, so update state */

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

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

    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 nMCU;

}

/*

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

 */

METHODDEF(void)

finish_pass_huff(j_compress_ptr cinfo)

{

  lhuff_entropy_ptr entropy = (lhuff_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;

  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;

  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

/*

 * Trial-encode nMCU MCUs' worth of Huffman-compressed differences.

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

 */

METHODDEF(JDIMENSION)

encode_mcus_gather(j_compress_ptr cinfo, JDIFFIMAGE diff_buf,

                   JDIMENSION MCU_row_num, JDIMENSION MCU_col_num,

                   JDIMENSION nMCU)

{

  lhuff_entropy_ptr entropy = (lhuff_entropy_ptr)cinfo->entropy;

  int sampn, ci, yoffset, MCU_width, ptrn;

  JDIMENSION mcu_num;

  /* Take care of restart intervals if needed */

  if (cinfo->restart_interval) {

    if (entropy->restarts_to_go == 0) {

      /* Update restart state */

      entropy->restarts_to_go = cinfo->restart_interval;

    }

    entropy->restarts_to_go--;

  }

  /* Set input pointer locations based on MCU_col_num */

  for (ptrn = 0; ptrn < entropy->num_input_ptrs; ptrn++) {

    ci = entropy->input_ptr_info[ptrn].ci;

    yoffset = entropy->input_ptr_info[ptrn].yoffset;

    MCU_width = entropy->input_ptr_info[ptrn].MCU_width;

    entropy->input_ptr[ptrn] =

      diff_buf[ci][MCU_row_num + yoffset] + (MCU_col_num * MCU_width);

  }

  for (mcu_num = 0; mcu_num < nMCU; mcu_num++) {

    /* Inner loop handles the samples in the MCU */

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

      register int temp;

      register int nbits;

      long *counts = entropy->cur_counts[sampn];

      /* Encode the difference per section H.1.2.2 */

      /* Input the sample difference */

      temp = *entropy->input_ptr[entropy->input_ptr_index[sampn]]++;

      if (temp & 0x8000) {      /* instead of temp < 0 */

        temp = (-temp) & 0x7FFF; /* absolute value, mod 2^16 */

        if (temp == 0)          /* special case: magnitude = 32768 */

          temp = 0x8000;

      } else

        temp &= 0x7FFF;         /* abs value mod 2^16 */

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

      nbits = 0;

      while (temp) {

        nbits++;

        temp >>= 1;

      }

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

       */

      if (nbits > MAX_DIFF_BITS)

        ERREXIT(cinfo, JERR_BAD_DCT_COEF);

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

      counts[nbits]++;

    }

  }

  return nMCU;

}

/*

 * Finish up a statistics-gathering pass and create the new Huffman tables.

 */

METHODDEF(void)

finish_pass_gather(j_compress_ptr cinfo)

{

  lhuff_entropy_ptr entropy = (lhuff_entropy_ptr)cinfo->entropy;

  int ci, dctbl;

  jpeg_component_info *compptr;

  JHUFF_TBL **htblptr;

  boolean did_dc[NUM_HUFF_TBLS];

  /* It's important not to apply jpeg_gen_optimal_table more than once

   * per table, because it clobbers the input frequency counts!

   */

  memset(did_dc, 0, sizeof(did_dc));

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

    compptr = cinfo->cur_comp_info[ci];

    dctbl = compptr->dc_tbl_no;

    if (!did_dc[dctbl]) {

      htblptr = &cinfo->dc_huff_tbl_ptrs[dctbl];

      if (*htblptr == NULL)

        *htblptr = jpeg_alloc_huff_table((j_common_ptr)cinfo);

      jpeg_gen_optimal_table(cinfo, *htblptr, entropy->count_ptrs[dctbl]);

      did_dc[dctbl] = TRUE;

    }

  }

}

#endif /* ENTROPY_OPT_SUPPORTED */

/*

 * Module initialization routine for Huffman entropy encoding.

 */

GLOBAL(void)

jinit_lhuff_encoder(j_compress_ptr cinfo)

{

  lhuff_entropy_ptr entropy;

  int i;

  entropy = (lhuff_entropy_ptr)

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

                                sizeof(lhuff_entropy_encoder));

  cinfo->entropy = (struct jpeg_entropy_encoder *)entropy;

  entropy->pub.start_pass = start_pass_lhuff;

  /* Mark tables unallocated */

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

    entropy->derived_tbls[i] = NULL;

#ifdef ENTROPY_OPT_SUPPORTED

    entropy->count_ptrs[i] = NULL;

#endif

  }

}

#endif /* C_LOSSLESS_SUPPORTED */