doom3-bfg/neo/renderer/jpeg-6/jcphuff.cpp

/*
 * jcphuff.c
 *
 * Copyright (C) 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 for progressive JPEG.
 *
 * We do not support output suspension in this module, since the library
 * currently does not allow multiple-scan files to be written with output
 * suspension.
 */

#define JPEG_INTERNALS
#include "jinclude.h"
#include "jpeglib.h"
#include "jchuff.h"      /* Declarations shared with jchuff.c */

#ifdef C_PROGRESSIVE_SUPPORTED

/* Expanded entropy encoder object for progressive Huffman encoding. */

typedef struct {
    struct jpeg_entropy_encoder pub;/* public fields */

    /* Mode flag: TRUE for optimization, FALSE for actual data output */
    boolean gather_statistics;

    /* Bit-level coding status.
     * next_output_byte/free_in_buffer are local copies of cinfo->dest fields.
     */
    JOCTET *       next_output_byte; /* => next byte to write in buffer */
    size_t         free_in_buffer; /* # of byte spaces remaining in buffer */
    INT32          put_buffer; /* current bit-accumulation buffer */
    int            put_bits; /* # of bits now in it */
    j_compress_ptr cinfo;   /* link to cinfo (needed for dump_buffer) */

    /* Coding status for DC components */
    int last_dc_val[MAX_COMPS_IN_SCAN];/* last DC coef for each component */

    /* Coding status for AC components */
    int          ac_tbl_no; /* the table number of the single component */
    unsigned int EOBRUN;    /* run length of EOBs */
    unsigned int BE;    /* # of buffered correction bits before MCU */
    char *       bit_buffer;/* buffer for correction bits (1 per char) */
    /* packing correction bits tightly would save some space but cost time... */

    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).
     * Since any one scan codes only DC or only AC, we only need one set
     * of tables, not one for DC and one for AC.
     */
    c_derived_tbl * derived_tbls[NUM_HUFF_TBLS];

    /* Statistics tables for optimization; again, one set is enough */
    long * count_ptrs[NUM_HUFF_TBLS];
} phuff_entropy_encoder;

typedef phuff_entropy_encoder * phuff_entropy_ptr;

/* MAX_CORR_BITS is the number of bits the AC refinement correction-bit
 * buffer can hold.  Larger sizes may slightly improve compression, but
 * 1000 is already well into the realm of overkill.
 * The minimum safe size is 64 bits.
 */

#define MAX_CORR_BITS  1000 /* Max # of correction bits I can buffer */

/* IRIGHT_SHIFT is like RIGHT_SHIFT, but works on int rather than INT32.
 * We assume that int right shift is unsigned if INT32 right shift is,
 * which should be safe.
 */

#ifdef RIGHT_SHIFT_IS_UNSIGNED
#define ISHIFT_TEMPS    int ishift_temp;
#define IRIGHT_SHIFT( x, shft )  \
    ( ( ishift_temp = ( x ) ) < 0 ? \
                      ( ishift_temp >> ( shft ) ) | ( ( ~0 ) << ( 16 - ( shft ) ) ) : \
                      ( ishift_temp >> ( shft ) ) )
#else
#define ISHIFT_TEMPS
#define IRIGHT_SHIFT( x, shft )    ( ( x ) >> ( shft ) )
#endif

/* Forward declarations */
METHODDEF boolean encode_mcu_DC_first JPP( ( j_compress_ptr cinfo,
                                             JBLOCKROW * MCU_data ) );
METHODDEF boolean encode_mcu_AC_first JPP( ( j_compress_ptr cinfo,
                                             JBLOCKROW * MCU_data ) );
METHODDEF boolean encode_mcu_DC_refine JPP( ( j_compress_ptr cinfo,
                                              JBLOCKROW * MCU_data ) );
METHODDEF boolean encode_mcu_AC_refine JPP( ( j_compress_ptr cinfo,
                                              JBLOCKROW * MCU_data ) );
METHODDEF void finish_pass_phuff JPP( (j_compress_ptr cinfo) );
METHODDEF void finish_pass_gather_phuff JPP( (j_compress_ptr cinfo) );


/*
 * Initialize for a Huffman-compressed scan using progressive JPEG.
 */

METHODDEF void
start_pass_phuff( j_compress_ptr cinfo, boolean gather_statistics ) {
    phuff_entropy_ptr entropy = (phuff_entropy_ptr) cinfo->entropy;
    boolean is_DC_band;
    int ci, tbl;
    jpeg_component_info * compptr;

    entropy->cinfo = cinfo;
    entropy->gather_statistics = gather_statistics;

    is_DC_band = ( cinfo->Ss == 0 );

    /* We assume jcmaster.c already validated the scan parameters. */

    /* Select execution routines */
    if ( cinfo->Ah == 0 ) {
        if ( is_DC_band ) {
            entropy->pub.encode_mcu = encode_mcu_DC_first;
        } else {
            entropy->pub.encode_mcu = encode_mcu_AC_first;
        }
    } else {
        if ( is_DC_band ) {
            entropy->pub.encode_mcu = encode_mcu_DC_refine;
        } else {
            entropy->pub.encode_mcu = encode_mcu_AC_refine;
            /* AC refinement needs a correction bit buffer */
            if ( entropy->bit_buffer == NULL ) {
                entropy->bit_buffer = (char *)
                                      ( *cinfo->mem->alloc_small )( (j_common_ptr) cinfo, JPOOL_IMAGE,
                                                                   MAX_CORR_BITS * SIZEOF( char ) );
            }
        }
    }
    if ( gather_statistics ) {
        entropy->pub.finish_pass = finish_pass_gather_phuff;
    } else {
        entropy->pub.finish_pass = finish_pass_phuff;
    }

    /* Only DC coefficients may be interleaved, so cinfo->comps_in_scan = 1
     * for AC coefficients.
     */
    for ( ci = 0; ci < cinfo->comps_in_scan; ci++ ) {
        compptr = cinfo->cur_comp_info[ci];
        /* Initialize DC predictions to 0 */
        entropy->last_dc_val[ci] = 0;
        /* Make sure requested tables are present */
        /* (In gather mode, tables need not be allocated yet) */
        if ( is_DC_band ) {
            if ( cinfo->Ah != 0 ) {/* DC refinement needs no table */
                continue;
            }
            tbl = compptr->dc_tbl_no;
            if ( ( tbl < 0 ) || ( tbl >= NUM_HUFF_TBLS ) ||
                ( ( cinfo->dc_huff_tbl_ptrs[tbl] == NULL ) && ( !gather_statistics ) ) ) {
                ERREXIT1( cinfo, JERR_NO_HUFF_TABLE, tbl );
            }
        } else {
            entropy->ac_tbl_no = tbl = compptr->ac_tbl_no;
            if ( ( tbl < 0 ) || ( tbl >= NUM_HUFF_TBLS ) ||
                ( ( cinfo->ac_huff_tbl_ptrs[tbl] == NULL ) && ( !gather_statistics ) ) ) {
                ERREXIT1( cinfo, JERR_NO_HUFF_TABLE, tbl );
            }
        }
        if ( gather_statistics ) {
            /* Allocate and zero the statistics tables */
            /* Note that jpeg_gen_optimal_table expects 257 entries in each table! */
            if ( entropy->count_ptrs[tbl] == NULL ) {
                entropy->count_ptrs[tbl] = (long *)
                                           ( *cinfo->mem->alloc_small )( (j_common_ptr) cinfo, JPOOL_IMAGE,
                                                                        257 * SIZEOF( long ) );
            }
            MEMZERO( entropy->count_ptrs[tbl], 257 * SIZEOF( long ) );
        } else {
            /* Compute derived values for Huffman tables */
            /* We may do this more than once for a table, but it's not expensive */
            if ( is_DC_band ) {
                jpeg_make_c_derived_tbl( cinfo, cinfo->dc_huff_tbl_ptrs[tbl],
                                         &entropy->derived_tbls[tbl] );
            } else {
                jpeg_make_c_derived_tbl( cinfo, cinfo->ac_huff_tbl_ptrs[tbl],
                                         &entropy->derived_tbls[tbl] );
            }
        }
    }

    /* Initialize AC stuff */
    entropy->EOBRUN = 0;
    entropy->BE = 0;

    /* Initialize bit buffer to empty */
    entropy->put_buffer = 0;
    entropy->put_bits = 0;

    /* Initialize restart stuff */
    entropy->restarts_to_go = cinfo->restart_interval;
    entropy->next_restart_num = 0;
}


/* Outputting bytes to the file.
 * NB: these must be called only when actually outputting,
 * that is, entropy->gather_statistics == FALSE.
 */

/* Emit a byte */
#define emit_byte( entropy, val )  \
    { *( entropy )->next_output_byte++ = (JOCTET) ( val );  \
      if ( -- ( entropy )->free_in_buffer == 0 ) { \
          dump_buffer( entropy ); } }


LOCAL void
dump_buffer( phuff_entropy_ptr entropy ) {
/* Empty the output buffer; we do not support suspension in this module. */
    struct jpeg_destination_mgr * dest = entropy->cinfo->dest;

    if ( !( *dest->empty_output_buffer )( entropy->cinfo ) ) {
        ERREXIT( entropy->cinfo, JERR_CANT_SUSPEND );
    }
    /* After a successful buffer dump, must reset buffer pointers */
    entropy->next_output_byte = dest->next_output_byte;
    entropy->free_in_buffer = dest->free_in_buffer;
}


/* 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 void
emit_bits( phuff_entropy_ptr entropy, unsigned int code, int size ) {
/* Emit some bits, unless we are in gather mode */
/* This routine is heavily used, so it's worth coding tightly. */
    register INT32 put_buffer = (INT32) code;
    register int put_bits = entropy->put_bits;

    /* if size is 0, caller used an invalid Huffman table entry */
    if ( size == 0 ) {
        ERREXIT( entropy->cinfo, JERR_HUFF_MISSING_CODE );
    }

    if ( entropy->gather_statistics ) {
        return;
    }               /* do nothing if we're only getting stats */

    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 |= entropy->put_buffer;/* and merge with old buffer contents */

    while ( put_bits >= 8 ) {
        int c = (int) ( ( put_buffer >> 16 ) & 0xFF );

        emit_byte( entropy, c );
        if ( c == 0xFF ) {  /* need to stuff a zero byte? */
            emit_byte( entropy, 0 );
        }
        put_buffer <<= 8;
        put_bits -= 8;
    }

    entropy->put_buffer = put_buffer;/* update variables */
    entropy->put_bits = put_bits;
}


LOCAL void
flush_bits( phuff_entropy_ptr entropy ) {
    emit_bits( entropy, 0x7F, 7 );/* fill any partial byte with ones */
    entropy->put_buffer = 0;   /* and reset bit-buffer to empty */
    entropy->put_bits = 0;
}


/*
 * Emit (or just count) a Huffman symbol.
 */

INLINE
LOCAL void
emit_symbol( phuff_entropy_ptr entropy, int tbl_no, int symbol ) {
    if ( entropy->gather_statistics ) {
        entropy->count_ptrs[tbl_no][symbol]++;
    } else {
        c_derived_tbl * tbl = entropy->derived_tbls[tbl_no];
        emit_bits( entropy, tbl->ehufco[symbol], tbl->ehufsi[symbol] );
    }
}


/*
 * Emit bits from a correction bit buffer.
 */

LOCAL void
emit_buffered_bits( phuff_entropy_ptr entropy, char * bufstart,
                    unsigned int nbits ) {
    if ( entropy->gather_statistics ) {
        return;
    }               /* no real work */

    while ( nbits > 0 ) {
        emit_bits( entropy, (unsigned int) ( *bufstart ), 1 );
        bufstart++;
        nbits--;
    }
}


/*
 * Emit any pending EOBRUN symbol.
 */

LOCAL void
emit_eobrun( phuff_entropy_ptr entropy ) {
    register int temp, nbits;

    if ( entropy->EOBRUN > 0 ) {/* if there is any pending EOBRUN */
        temp = entropy->EOBRUN;
        nbits = 0;
        while ( ( temp >>= 1 ) ) {
            nbits++;
        }

        emit_symbol( entropy, entropy->ac_tbl_no, nbits << 4 );
        if ( nbits ) {
            emit_bits( entropy, entropy->EOBRUN, nbits );
        }

        entropy->EOBRUN = 0;

        /* Emit any buffered correction bits */
        emit_buffered_bits( entropy, entropy->bit_buffer, entropy->BE );
        entropy->BE = 0;
    }
}


/*
 * Emit a restart marker & resynchronize predictions.
 */

LOCAL void
emit_restart( phuff_entropy_ptr entropy, int restart_num ) {
    int ci;

    emit_eobrun( entropy );

    if ( !entropy->gather_statistics ) {
        flush_bits( entropy );
        emit_byte( entropy, 0xFF );
        emit_byte( entropy, JPEG_RST0 + restart_num );
    }

    if ( entropy->cinfo->Ss == 0 ) {
        /* Re-initialize DC predictions to 0 */
        for ( ci = 0; ci < entropy->cinfo->comps_in_scan; ci++ ) {
            entropy->last_dc_val[ci] = 0;
        }
    } else {
        /* Re-initialize all AC-related fields to 0 */
        entropy->EOBRUN = 0;
        entropy->BE = 0;
    }
}


/*
 * MCU encoding for DC initial scan (either spectral selection,
 * or first pass of successive approximation).
 */

METHODDEF boolean
encode_mcu_DC_first( j_compress_ptr cinfo, JBLOCKROW * MCU_data ) {
    phuff_entropy_ptr entropy = (phuff_entropy_ptr) cinfo->entropy;
    register int temp, temp2;
    register int nbits;
    int blkn, ci;
    int Al = cinfo->Al;
    JBLOCKROW block;
    jpeg_component_info * compptr;
    ISHIFT_TEMPS

    entropy->next_output_byte = cinfo->dest->next_output_byte;
    entropy->free_in_buffer = cinfo->dest->free_in_buffer;

    /* Emit restart marker if needed */
    if ( cinfo->restart_interval ) {
        if ( entropy->restarts_to_go == 0 ) {
            emit_restart( entropy, entropy->next_restart_num );
        }
    }

    /* Encode the MCU data blocks */
    for ( blkn = 0; blkn < cinfo->blocks_in_MCU; blkn++ ) {
        block = MCU_data[blkn];
        ci = cinfo->MCU_membership[blkn];
        compptr = cinfo->cur_comp_info[ci];

        /* Compute the DC value after the required point transform by Al.
         * This is simply an arithmetic right shift.
         */
        temp2 = IRIGHT_SHIFT( (int) ( ( *block )[0] ), Al );

        /* DC differences are figured on the point-transformed values. */
        temp = temp2 - entropy->last_dc_val[ci];
        entropy->last_dc_val[ci] = temp2;

        /* Encode the DC coefficient difference per section G.1.2.1 */
        temp2 = temp;
        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;
        }

        /* Count/emit the Huffman-coded symbol for the number of bits */
        emit_symbol( entropy, compptr->dc_tbl_no, nbits );

        /* 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 */
            emit_bits( entropy, (unsigned int) temp2, nbits );
        }
    }

    cinfo->dest->next_output_byte = entropy->next_output_byte;
    cinfo->dest->free_in_buffer = entropy->free_in_buffer;

    /* 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;
}


/*
 * MCU encoding for AC initial scan (either spectral selection,
 * or first pass of successive approximation).
 */

METHODDEF boolean
encode_mcu_AC_first( j_compress_ptr cinfo, JBLOCKROW * MCU_data ) {
    phuff_entropy_ptr entropy = (phuff_entropy_ptr) cinfo->entropy;
    register int temp, temp2;
    register int nbits;
    register int r, k;
    int Se = cinfo->Se;
    int Al = cinfo->Al;
    JBLOCKROW block;

    entropy->next_output_byte = cinfo->dest->next_output_byte;
    entropy->free_in_buffer = cinfo->dest->free_in_buffer;

    /* Emit restart marker if needed */
    if ( cinfo->restart_interval ) {
        if ( entropy->restarts_to_go == 0 ) {
            emit_restart( entropy, entropy->next_restart_num );
        }
    }

    /* Encode the MCU data block */
    block = MCU_data[0];

    /* Encode the AC coefficients per section G.1.2.2, fig. G.3 */

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

    for ( k = cinfo->Ss; k <= Se; k++ ) {
        if ( ( temp = ( *block )[jpeg_natural_order[k]] ) == 0 ) {
            r++;
            continue;
        }
        /* We must apply the point transform by Al.  For AC coefficients this
         * is an integer division with rounding towards 0.  To do this portably
         * in C, we shift after obtaining the absolute value; so the code is
         * interwoven with finding the abs value (temp) and output bits (temp2).
         */
        if ( temp < 0 ) {
            temp = -temp;/* temp is abs value of input */
            temp >>= Al;/* apply the point transform */
            /* For a negative coef, want temp2 = bitwise complement of abs(coef) */
            temp2 = ~temp;
        } else {
            temp >>= Al;/* apply the point transform */
            temp2 = temp;
        }
        /* Watch out for case that nonzero coef is zero after point transform */
        if ( temp == 0 ) {
            r++;
            continue;
        }

        /* Emit any pending EOBRUN */
        if ( entropy->EOBRUN > 0 ) {
            emit_eobrun( entropy );
        }
        /* if run length > 15, must emit special run-length-16 codes (0xF0) */
        while ( r > 15 ) {
            emit_symbol( entropy, entropy->ac_tbl_no, 0xF0 );
            r -= 16;
        }

        /* 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/emit Huffman symbol for run length / number of bits */
        emit_symbol( entropy, entropy->ac_tbl_no, ( r << 4 ) + nbits );

        /* Emit that number of bits of the value, if positive, */
        /* or the complement of its magnitude, if negative. */
        emit_bits( entropy, (unsigned int) temp2, nbits );

        r = 0;      /* reset zero run length */
    }

    if ( r > 0 ) {      /* If there are trailing zeroes, */
        entropy->EOBRUN++;  /* count an EOB */
        if ( entropy->EOBRUN == 0x7FFF ) {
            emit_eobrun( entropy );
        }                   /* force it out to avoid overflow */
    }

    cinfo->dest->next_output_byte = entropy->next_output_byte;
    cinfo->dest->free_in_buffer = entropy->free_in_buffer;

    /* 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;
}


/*
 * MCU encoding for DC successive approximation refinement scan.
 * Note: we assume such scans can be multi-component, although the spec
 * is not very clear on the point.
 */

METHODDEF boolean
encode_mcu_DC_refine( j_compress_ptr cinfo, JBLOCKROW * MCU_data ) {
    phuff_entropy_ptr entropy = (phuff_entropy_ptr) cinfo->entropy;
    register int temp;
    int blkn;
    int Al = cinfo->Al;
    JBLOCKROW block;

    entropy->next_output_byte = cinfo->dest->next_output_byte;
    entropy->free_in_buffer = cinfo->dest->free_in_buffer;

    /* Emit restart marker if needed */
    if ( cinfo->restart_interval ) {
        if ( entropy->restarts_to_go == 0 ) {
            emit_restart( entropy, entropy->next_restart_num );
        }
    }

    /* Encode the MCU data blocks */
    for ( blkn = 0; blkn < cinfo->blocks_in_MCU; blkn++ ) {
        block = MCU_data[blkn];

        /* We simply emit the Al'th bit of the DC coefficient value. */
        temp = ( *block )[0];
        emit_bits( entropy, (unsigned int) ( temp >> Al ), 1 );
    }

    cinfo->dest->next_output_byte = entropy->next_output_byte;
    cinfo->dest->free_in_buffer = entropy->free_in_buffer;

    /* 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;
}


/*
 * MCU encoding for AC successive approximation refinement scan.
 */

METHODDEF boolean
encode_mcu_AC_refine( j_compress_ptr cinfo, JBLOCKROW * MCU_data ) {
    phuff_entropy_ptr entropy = (phuff_entropy_ptr) cinfo->entropy;
    register int temp;
    register int r, k;
    int EOB;
    char * BR_buffer;
    unsigned int BR;
    int Se = cinfo->Se;
    int Al = cinfo->Al;
    JBLOCKROW block;
    int absvalues[DCTSIZE2];

    entropy->next_output_byte = cinfo->dest->next_output_byte;
    entropy->free_in_buffer = cinfo->dest->free_in_buffer;

    /* Emit restart marker if needed */
    if ( cinfo->restart_interval ) {
        if ( entropy->restarts_to_go == 0 ) {
            emit_restart( entropy, entropy->next_restart_num );
        }
    }

    /* Encode the MCU data block */
    block = MCU_data[0];

    /* It is convenient to make a pre-pass to determine the transformed
     * coefficients' absolute values and the EOB position.
     */
    EOB = 0;
    for ( k = cinfo->Ss; k <= Se; k++ ) {
        temp = ( *block )[jpeg_natural_order[k]];
        /* We must apply the point transform by Al.  For AC coefficients this
         * is an integer division with rounding towards 0.  To do this portably
         * in C, we shift after obtaining the absolute value.
         */
        if ( temp < 0 ) {
            temp = -temp;
        }               /* temp is abs value of input */
        temp >>= Al;    /* apply the point transform */
        absvalues[k] = temp;/* save abs value for main pass */
        if ( temp == 1 ) {
            EOB = k;
        }               /* EOB = index of last newly-nonzero coef */
    }

    /* Encode the AC coefficients per section G.1.2.3, fig. G.7 */

    r = 0;          /* r = run length of zeros */
    BR = 0;         /* BR = count of buffered bits added now */
    BR_buffer = entropy->bit_buffer + entropy->BE;/* Append bits to buffer */

    for ( k = cinfo->Ss; k <= Se; k++ ) {
        if ( ( temp = absvalues[k] ) == 0 ) {
            r++;
            continue;
        }

        /* Emit any required ZRLs, but not if they can be folded into EOB */
        while ( r > 15 && k <= EOB ) {
            /* emit any pending EOBRUN and the BE correction bits */
            emit_eobrun( entropy );
            /* Emit ZRL */
            emit_symbol( entropy, entropy->ac_tbl_no, 0xF0 );
            r -= 16;
            /* Emit buffered correction bits that must be associated with ZRL */
            emit_buffered_bits( entropy, BR_buffer, BR );
            BR_buffer = entropy->bit_buffer;/* BE bits are gone now */
            BR = 0;
        }

        /* If the coef was previously nonzero, it only needs a correction bit.
         * NOTE: a straight translation of the spec's figure G.7 would suggest
         * that we also need to test r > 15.  But if r > 15, we can only get here
         * if k > EOB, which implies that this coefficient is not 1.
         */
        if ( temp > 1 ) {
            /* The correction bit is the next bit of the absolute value. */
            BR_buffer[BR++] = (char) ( temp & 1 );
            continue;
        }

        /* Emit any pending EOBRUN and the BE correction bits */
        emit_eobrun( entropy );

        /* Count/emit Huffman symbol for run length / number of bits */
        emit_symbol( entropy, entropy->ac_tbl_no, ( r << 4 ) + 1 );

        /* Emit output bit for newly-nonzero coef */
        temp = ( ( *block )[jpeg_natural_order[k]] < 0 ) ? 0 : 1;
        emit_bits( entropy, (unsigned int) temp, 1 );

        /* Emit buffered correction bits that must be associated with this code */
        emit_buffered_bits( entropy, BR_buffer, BR );
        BR_buffer = entropy->bit_buffer;/* BE bits are gone now */
        BR = 0;
        r = 0;      /* reset zero run length */
    }

    if ( ( r > 0 ) || ( BR > 0 ) ) {/* If there are trailing zeroes, */
        entropy->EOBRUN++;  /* count an EOB */
        entropy->BE += BR;  /* concat my correction bits to older ones */
        /* We force out the EOB if we risk either:
         * 1. overflow of the EOB counter;
         * 2. overflow of the correction bit buffer during the next MCU.
         */
        if ( ( entropy->EOBRUN == 0x7FFF ) || ( entropy->BE > ( MAX_CORR_BITS - DCTSIZE2 + 1 ) ) ) {
            emit_eobrun( entropy );
        }
    }

    cinfo->dest->next_output_byte = entropy->next_output_byte;
    cinfo->dest->free_in_buffer = entropy->free_in_buffer;

    /* 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 progressive scan.
 */

METHODDEF void
finish_pass_phuff( j_compress_ptr cinfo ) {
    phuff_entropy_ptr entropy = (phuff_entropy_ptr) cinfo->entropy;

    entropy->next_output_byte = cinfo->dest->next_output_byte;
    entropy->free_in_buffer = cinfo->dest->free_in_buffer;

    /* Flush out any buffered data */
    emit_eobrun( entropy );
    flush_bits( entropy );

    cinfo->dest->next_output_byte = entropy->next_output_byte;
    cinfo->dest->free_in_buffer = entropy->free_in_buffer;
}


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

METHODDEF void
finish_pass_gather_phuff( j_compress_ptr cinfo ) {
    phuff_entropy_ptr entropy = (phuff_entropy_ptr) cinfo->entropy;
    boolean is_DC_band;
    int ci, tbl;
    jpeg_component_info * compptr;
    JHUFF_TBL ** htblptr;
    boolean did[NUM_HUFF_TBLS];

    /* Flush out buffered data (all we care about is counting the EOB symbol) */
    emit_eobrun( entropy );

    is_DC_band = ( cinfo->Ss == 0 );

    /* It's important not to apply jpeg_gen_optimal_table more than once
     * per table, because it clobbers the input frequency counts!
     */
    MEMZERO( did, SIZEOF( did ) );

    for ( ci = 0; ci < cinfo->comps_in_scan; ci++ ) {
        compptr = cinfo->cur_comp_info[ci];
        if ( is_DC_band ) {
            if ( cinfo->Ah != 0 ) {/* DC refinement needs no table */
                continue;
            }
            tbl = compptr->dc_tbl_no;
        } else {
            tbl = compptr->ac_tbl_no;
        }
        if ( !did[tbl] ) {
            if ( is_DC_band ) {
                htblptr = &cinfo->dc_huff_tbl_ptrs[tbl];
            } else {
                htblptr = &cinfo->ac_huff_tbl_ptrs[tbl];
            }
            if ( *htblptr == NULL ) {
                *htblptr = jpeg_alloc_huff_table( (j_common_ptr) cinfo );
            }
            jpeg_gen_optimal_table( cinfo, *htblptr, entropy->count_ptrs[tbl] );
            did[tbl] = TRUE;
        }
    }
}


/*
 * Module initialization routine for progressive Huffman entropy encoding.
 */

GLOBAL void
jinit_phuff_encoder( j_compress_ptr cinfo ) {
    phuff_entropy_ptr entropy;
    int i;

    entropy = (phuff_entropy_ptr)
              ( *cinfo->mem->alloc_small )( (j_common_ptr) cinfo, JPOOL_IMAGE,
                                           SIZEOF( phuff_entropy_encoder ) );
    cinfo->entropy = (struct jpeg_entropy_encoder *) entropy;
    entropy->pub.start_pass = start_pass_phuff;

    /* Mark tables unallocated */
    for ( i = 0; i < NUM_HUFF_TBLS; i++ ) {
        entropy->derived_tbls[i] = NULL;
        entropy->count_ptrs[i] = NULL;
    }
    entropy->bit_buffer = NULL; /* needed only in AC refinement scan */
}

#endif /* C_PROGRESSIVE_SUPPORTED */