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jclhuff.c (18635B)

---

/*
* 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, 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];
       entropy->cur_counts[sampn] = entropy->count_ptrs[compptr->dc_tbl_no];
     }
   }
 }
 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 */