DOOM-3-BFG

jchuff.cpp (28629B)

---

 /*
  * jchuff.c
  *
  * Copyright (C) 1991-1995, Thomas G. Lane.
  * This file is part of the Independent JPEG Group's software.
  * For conditions of distribution and use, see the accompanying README file.
  *
  * This file contains Huffman entropy 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.
  */
 
 #define JPEG_INTERNALS
 #include "jinclude.h"
 #include "jpeglib.h"
 #include "jchuff.h"      /* Declarations shared with jcphuff.c */
 
 
 /* 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];
 
 #ifdef ENTROPY_OPT_SUPPORTED    /* Statistics tables for optimization */
     long * dc_count_ptrs[NUM_HUFF_TBLS];
     long * ac_count_ptrs[NUM_HUFF_TBLS];
 #endif
 } 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 JPP( ( j_compress_ptr cinfo,
                                          JBLOCKROW * MCU_data ) );
 METHODDEF void finish_pass_huff JPP( (j_compress_ptr cinfo) );
 #ifdef ENTROPY_OPT_SUPPORTED
 METHODDEF boolean encode_mcu_gather JPP( ( j_compress_ptr cinfo,
                                            JBLOCKROW * MCU_data ) );
 METHODDEF void finish_pass_gather JPP( (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;
     }
 
     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;
         /* Make sure requested tables are present */
         /* (In gather mode, tables need not be allocated yet) */
         if ( ( dctbl < 0 ) || ( dctbl >= NUM_HUFF_TBLS ) ||
             ( ( cinfo->dc_huff_tbl_ptrs[dctbl] == NULL ) && ( !gather_statistics ) ) ) {
             ERREXIT1( cinfo, JERR_NO_HUFF_TABLE, dctbl );
         }
         if ( ( actbl < 0 ) || ( actbl >= NUM_HUFF_TBLS ) ||
             ( ( cinfo->ac_huff_tbl_ptrs[actbl] == NULL ) && ( !gather_statistics ) ) ) {
             ERREXIT1( cinfo, JERR_NO_HUFF_TABLE, actbl );
         }
         if ( gather_statistics ) {
 #ifdef ENTROPY_OPT_SUPPORTED
             /* 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, cinfo->dc_huff_tbl_ptrs[dctbl],
                                      &entropy->dc_derived_tbls[dctbl] );
             jpeg_make_c_derived_tbl( cinfo, cinfo->ac_huff_tbl_ptrs[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.
  * Note this is also used by jcphuff.c.
  */
 
 GLOBAL void
 jpeg_make_c_derived_tbl( j_compress_ptr cinfo, JHUFF_TBL * htbl,
                          c_derived_tbl ** pdtbl ) {
     c_derived_tbl * dtbl;
     int p, i, l, lastp, si;
     char huffsize[257];
     unsigned int huffcode[257];
     unsigned int code;
 
     /* 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 */
     /* Note that this is in code-length order. */
 
     p = 0;
     for ( l = 1; l <= 16; l++ ) {
         for ( i = 1; i <= (int) htbl->bits[l]; i++ ) {
             huffsize[p++] = (char) l;
         }
     }
     huffsize[p] = 0;
     lastp = p;
 
     /* Figure C.2: generate the codes themselves */
     /* Note that this is in code-length order. */
 
     code = 0;
     si = huffsize[0];
     p = 0;
     while ( huffsize[p] ) {
         while ( ( (int) huffsize[p] ) == si ) {
             huffcode[p++] = code;
             code++;
         }
         code <<= 1;
         si++;
     }
 
     /* Figure C.3: generate encoding tables */
     /* These are code and size indexed by symbol value */
 
     /* Set any codeless symbols to have code length 0;
      * this allows emit_bits to detect any attempt to emit such symbols.
      */
     MEMZERO( dtbl->ehufsi, SIZEOF( dtbl->ehufsi ) );
 
     for ( p = 0; p < lastp; p++ ) {
         dtbl->ehufco[htbl->huffval[p]] = huffcode[p];
         dtbl->ehufsi[htbl->huffval[p]] = 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 */
 
 /* 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 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 ) << 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;
 }
 
 
 /* Encode a single block's worth of coefficients */
 
 LOCAL boolean
 encode_one_block( working_state * state, JCOEFPTR block, int last_dc_val,
                   c_derived_tbl * dctbl, c_derived_tbl * actbl ) {
     register int temp, temp2;
     register int nbits;
     register int k, r, i;
 
     /* Encode the DC coefficient difference per section F.1.2.1 */
 
     temp = temp2 = block[0] - last_dc_val;
 
     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;
     }
 
     /* Emit the Huffman-coded symbol for the number of bits */
     if ( !emit_bits( state, dctbl->ehufco[nbits], dctbl->ehufsi[nbits] ) ) {
         return FALSE;
     }
 
     /* 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 */
         if ( !emit_bits( state, (unsigned int) temp2, nbits ) ) {
             return FALSE;
         }
     }
 
     /* 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 ) {
                 if ( !emit_bits( state, actbl->ehufco[0xF0], actbl->ehufsi[0xF0] ) ) {
                     return FALSE;
                 }
                 r -= 16;
             }
 
             temp2 = temp;
             if ( temp < 0 ) {
                 temp = -temp;/* temp is abs value of 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 = 1;  /* there must be at least one 1 bit */
             while ( ( temp >>= 1 ) ) {
                 nbits++;
             }
 
             /* Emit Huffman symbol for run length / number of bits */
             i = ( r << 4 ) + nbits;
             if ( !emit_bits( state, actbl->ehufco[i], actbl->ehufsi[i] ) ) {
                 return FALSE;
             }
 
             /* Emit that number of bits of the value, if positive, */
             /* or the complement of its magnitude, if negative. */
             if ( !emit_bits( state, (unsigned int) temp2, nbits ) ) {
                 return FALSE;
             }
 
             r = 0;
         }
     }
 
     /* If the last coef(s) were zero, emit an end-of-block code */
     if ( r > 0 ) {
         if ( !emit_bits( state, actbl->ehufco[0], actbl->ehufsi[0] ) ) {
             return FALSE;
         }
     }
 
     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 */
     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.
  *
  * This actually is optimization, in the sense that we find the best possible
  * Huffman table(s) for the given data.  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 an
  * optimal Huffman coding tree for the observed counts.
  *
  * 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 the JPEG spec.  This method is *not*
  * optimal; it may not choose the best possible limited-length code.  But
  * since the symbols involved are infrequently used, it's not clear that
  * going to extra trouble is worthwhile.
  */
 
 #ifdef ENTROPY_OPT_SUPPORTED
 
 
 /* Process a single block's worth of coefficients */
 
 LOCAL void
 htest_one_block( 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;
     }
 
     /* 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++;
             }
 
             /* 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( 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 optimal coding for the given counts, fill htbl.
  * Note this is also used by jcphuff.c.
  */
 
 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 there is 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 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 the JPEG spec 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 the JPEG spec 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++;
             }
         }
     }
 
     /* Set sent_table FALSE so updated table will be written to JPEG file. */
     htbl->sent_table = FALSE;
 }
 
 
 /*
  * Finish up a statistics-gathering pass and create the new Huffman tables.
  */
 
 METHODDEF void
 finish_pass_gather( j_compress_ptr cinfo ) {
     huff_entropy_ptr entropy = (huff_entropy_ptr) cinfo->entropy;
     int ci, dctbl, actbl;
     jpeg_component_info * compptr;
     JHUFF_TBL ** htblptr;
     boolean did_dc[NUM_HUFF_TBLS];
     boolean did_ac[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!
      */
     MEMZERO( did_dc, SIZEOF( did_dc ) );
     MEMZERO( did_ac, SIZEOF( did_ac ) );
 
     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 ( !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->dc_count_ptrs[dctbl] );
             did_dc[dctbl] = TRUE;
         }
         if ( !did_ac[actbl] ) {
             htblptr = &cinfo->ac_huff_tbl_ptrs[actbl];
             if ( *htblptr == NULL ) {
                 *htblptr = jpeg_alloc_huff_table( (j_common_ptr) cinfo );
             }
             jpeg_gen_optimal_table( cinfo, *htblptr, entropy->ac_count_ptrs[actbl] );
             did_ac[actbl] = TRUE;
         }
     }
 }
 
 
 #endif /* ENTROPY_OPT_SUPPORTED */
 
 
 /*
  * Module initialization routine for Huffman entropy encoding.
  */
 
 GLOBAL void
 jinit_huff_encoder( j_compress_ptr cinfo ) {
     huff_entropy_ptr entropy;
     int i;
 
     entropy = (huff_entropy_ptr)
               ( *cinfo->mem->alloc_small )( (j_common_ptr) cinfo, JPOOL_IMAGE,
                                            SIZEOF( huff_entropy_encoder ) );
     cinfo->entropy = (struct jpeg_entropy_encoder *) entropy;
     entropy->pub.start_pass = start_pass_huff;
 
     /* Mark tables unallocated */
     for ( i = 0; i < NUM_HUFF_TBLS; i++ ) {
         entropy->dc_derived_tbls[i] = entropy->ac_derived_tbls[i] = NULL;
 #ifdef ENTROPY_OPT_SUPPORTED
         entropy->dc_count_ptrs[i] = entropy->ac_count_ptrs[i] = NULL;
 #endif
     }
 }