/*
* 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
}
}