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+/*
+ * 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
+ }
+}