/*
 * jchuff.c
 *
 * This file was part of the Independent JPEG Group's software:
 * Copyright (C) 1991-1997, Thomas G. Lane.
 * libjpeg-turbo Modifications:
 * Copyright (C) 2009-2011, 2014-2016, D. R. Commander.
 * Copyright (C) 2015, Matthieu Darbois.
 * For conditions of distribution and use, see the accompanying README.ijg
 * 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 "jsimd.h"
#include "jconfigint.h"
#include <limits.h>

/*
 * NOTE: If USE_CLZ_INTRINSIC is defined, then clz/bsr instructions will be
 * used for bit counting rather than the lookup table.  This will reduce the
 * memory footprint by 64k, which is important for some mobile applications
 * that create many isolated instances of libjpeg-turbo (web browsers, for
 * instance.)  This may improve performance on some mobile platforms as well.
 * This feature is enabled by default only on ARM processors, because some x86
 * chips have a slow implementation of bsr, and the use of clz/bsr cannot be
 * shown to have a significant performance impact even on the x86 chips that
 * have a fast implementation of it.  When building for ARMv6, you can
 * explicitly disable the use of clz/bsr by adding -mthumb to the compiler
 * flags (this defines __thumb__).
 */

/* NOTE: Both GCC and Clang define __GNUC__ */
#if defined __GNUC__ && (defined __arm__ || defined __aarch64__)
#if !defined __thumb__ || defined __thumb2__
#define USE_CLZ_INTRINSIC
#endif
#endif

#ifdef USE_CLZ_INTRINSIC
#define JPEG_NBITS_NONZERO(x) (32 - __builtin_clz(x))
#define JPEG_NBITS(x) (x ? JPEG_NBITS_NONZERO(x) : 0)
#else
#include "jpeg_nbits_table.h"
#define JPEG_NBITS(x) (jpeg_nbits_table[x])
#define JPEG_NBITS_NONZERO(x) JPEG_NBITS(x)
#endif

#ifndef min
#define min(a, b) ((a)<(b)?(a):(b))
#endif


/* 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 {
	size_t 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

	int simd;
} 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(j_compress_ptr cinfo, JBLOCKROW *MCU_data);

METHODDEF(void) finish_pass_huff(j_compress_ptr cinfo);

#ifdef ENTROPY_OPT_SUPPORTED

METHODDEF(boolean) encode_mcu_gather(j_compress_ptr cinfo,
                                     JBLOCKROW *MCU_data);

METHODDEF(void) finish_pass_gather(j_compress_ptr cinfo);

#endif


/*
 * Initialize for a Huffman-compressed scan.
 * If gather_statistics is TRUE, we do not output anything during the scan,
 * just count the Huffman symbols used and generate Huffman code tables.
 */

METHODDEF(void)
start_pass_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;
	}

	entropy->simd = jsimd_can_huff_encode_one_block();

	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 (gather_statistics) {
#ifdef ENTROPY_OPT_SUPPORTED
			/* Check for invalid table indexes */
			/* (make_c_derived_tbl does this in the other path) */
			if (dctbl < 0 || dctbl >= NUM_HUFF_TBLS)
				ERREXIT1(cinfo, JERR_NO_HUFF_TABLE, dctbl);
			if (actbl < 0 || actbl >= NUM_HUFF_TBLS)
				ERREXIT1(cinfo, JERR_NO_HUFF_TABLE, actbl);
			/* 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, TRUE, dctbl,
			                        &entropy->dc_derived_tbls[dctbl]);
			jpeg_make_c_derived_tbl(cinfo, FALSE, 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.
 * This routine also performs some validation checks on the table.
 *
 * Note this is also used by jcphuff.c.
 */

GLOBAL(void)
jpeg_make_c_derived_tbl(j_compress_ptr cinfo, boolean isDC, int tblno,
                        c_derived_tbl **pdtbl) {
	JHUFF_TBL *htbl;
	c_derived_tbl *dtbl;
	int p, i, l, lastp, si, maxsymbol;
	char huffsize[257];
	unsigned int huffcode[257];
	unsigned int code;

	/* Note that huffsize[] and huffcode[] are filled in code-length order,
	 * paralleling the order of the symbols themselves in htbl->huffval[].
	 */

	/* Find the input Huffman table */
	if (tblno < 0 || tblno >= NUM_HUFF_TBLS)
		ERREXIT1(cinfo, JERR_NO_HUFF_TABLE, tblno);
	htbl =
			isDC ? cinfo->dc_huff_tbl_ptrs[tblno] : cinfo->ac_huff_tbl_ptrs[tblno];
	if (htbl == NULL)
		ERREXIT1(cinfo, JERR_NO_HUFF_TABLE, tblno);

	/* 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 */

	p = 0;
	for (l = 1; l <= 16; l++) {
		i = (int) htbl->bits[l];
		if (i < 0 || p + i > 256)   /* protect against table overrun */
			ERREXIT(cinfo, JERR_BAD_HUFF_TABLE);
		while (i--)
			huffsize[p++] = (char) l;
	}
	huffsize[p] = 0;
	lastp = p;

	/* Figure C.2: generate the codes themselves */
	/* We also validate that the counts represent a legal Huffman code tree. */

	code = 0;
	si = huffsize[0];
	p = 0;
	while (huffsize[p]) {
		while (((int) huffsize[p]) == si) {
			huffcode[p++] = code;
			code++;
		}
		/* code is now 1 more than the last code used for codelength si; but
		 * it must still fit in si bits, since no code is allowed to be all ones.
		 */
		if (((JLONG) code) >= (((JLONG) 1) << si))
			ERREXIT(cinfo, JERR_BAD_HUFF_TABLE);
		code <<= 1;
		si++;
	}

	/* Figure C.3: generate encoding tables */
	/* These are code and size indexed by symbol value */

	/* Set all codeless symbols to have code length 0;
	 * this lets us detect duplicate VAL entries here, and later
	 * allows emit_bits to detect any attempt to emit such symbols.
	 */
	MEMZERO(dtbl->ehufsi, sizeof(dtbl->ehufsi));

	/* This is also a convenient place to check for out-of-range
	 * and duplicated VAL entries.  We allow 0..255 for AC symbols
	 * but only 0..15 for DC.  (We could constrain them further
	 * based on data depth and mode, but this seems enough.)
	 */
	maxsymbol = isDC ? 15 : 255;

	for (p = 0; p < lastp; p++) {
		i = htbl->huffval[p];
		if (i < 0 || i > maxsymbol || dtbl->ehufsi[i])
			ERREXIT(cinfo, JERR_BAD_HUFF_TABLE);
		dtbl->ehufco[i] = huffcode[p];
		dtbl->ehufsi[i] = 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 */

/* These macros perform the same task as the emit_bits() function in the
 * original libjpeg code.  In addition to reducing overhead by explicitly
 * inlining the code, additional performance is achieved by taking into
 * account the size of the bit buffer and waiting until it is almost full
 * before emptying it.  This mostly benefits 64-bit platforms, since 6
 * bytes can be stored in a 64-bit bit buffer before it has to be emptied.
 */

#define EMIT_BYTE() { \
  JOCTET c; \
  put_bits -= 8; \
  c = (JOCTET)GETJOCTET(put_buffer >> put_bits); \
  *buffer++ = c; \
  if (c == 0xFF)  /* need to stuff a zero byte? */ \
    *buffer++ = 0; \
 }

#define PUT_BITS(code, size) { \
  put_bits += size; \
  put_buffer = (put_buffer << size) | code; \
}

#define CHECKBUF15() { \
  if (put_bits > 15) { \
    EMIT_BYTE() \
    EMIT_BYTE() \
  } \
}

#define CHECKBUF31() { \
  if (put_bits > 31) { \
    EMIT_BYTE() \
    EMIT_BYTE() \
    EMIT_BYTE() \
    EMIT_BYTE() \
  } \
}

#define CHECKBUF47() { \
  if (put_bits > 47) { \
    EMIT_BYTE() \
    EMIT_BYTE() \
    EMIT_BYTE() \
    EMIT_BYTE() \
    EMIT_BYTE() \
    EMIT_BYTE() \
  } \
}

#if !defined(_WIN32) && !defined(SIZEOF_SIZE_T)
#error Cannot determine word size
#endif

#if SIZEOF_SIZE_T == 8 || defined(_WIN64)

#define EMIT_BITS(code, size) { \
  CHECKBUF47() \
  PUT_BITS(code, size) \
}

#define EMIT_CODE(code, size) { \
  temp2 &= (((JLONG) 1)<<nbits) - 1; \
  CHECKBUF31() \
  PUT_BITS(code, size) \
  PUT_BITS(temp2, nbits) \
 }

#else

#define EMIT_BITS(code, size) { \
  PUT_BITS(code, size) \
  CHECKBUF15() \
}

#define EMIT_CODE(code, size) { \
  temp2 &= (((JLONG) 1)<<nbits) - 1; \
  PUT_BITS(code, size) \
  CHECKBUF15() \
  PUT_BITS(temp2, nbits) \
  CHECKBUF15() \
 }

#endif


/* Although it is exceedingly rare, it is possible for a Huffman-encoded
 * coefficient block to be larger than the 128-byte unencoded block.  For each
 * of the 64 coefficients, PUT_BITS is invoked twice, and each invocation can
 * theoretically store 16 bits (for a maximum of 2048 bits or 256 bytes per
 * encoded block.)  If, for instance, one artificially sets the AC
 * coefficients to alternating values of 32767 and -32768 (using the JPEG
 * scanning order-- 1, 8, 16, etc.), then this will produce an encoded block
 * larger than 200 bytes.
 */
#define BUFSIZE (DCTSIZE2 * 4)

#define LOAD_BUFFER() { \
  if (state->free_in_buffer < BUFSIZE) { \
    localbuf = 1; \
    buffer = _buffer; \
  } \
  else buffer = state->next_output_byte; \
 }

#define STORE_BUFFER() { \
  if (localbuf) { \
    bytes = buffer - _buffer; \
    buffer = _buffer; \
    while (bytes > 0) { \
      bytestocopy = min(bytes, state->free_in_buffer); \
      MEMCOPY(state->next_output_byte, buffer, bytestocopy); \
      state->next_output_byte += bytestocopy; \
      buffer += bytestocopy; \
      state->free_in_buffer -= bytestocopy; \
      if (state->free_in_buffer == 0) \
        if (! dump_buffer(state)) return FALSE; \
      bytes -= bytestocopy; \
    } \
  } \
  else { \
    state->free_in_buffer -= (buffer - state->next_output_byte); \
    state->next_output_byte = buffer; \
  } \
 }


LOCAL(boolean)
flush_bits(working_state *state) {
	JOCTET _buffer[BUFSIZE], *buffer;
	size_t put_buffer;
	int put_bits;
	size_t bytes, bytestocopy;
	int localbuf = 0;

	put_buffer = state->cur.put_buffer;
	put_bits = state->cur.put_bits;
	LOAD_BUFFER()

	/* fill any partial byte with ones */
	PUT_BITS(0x7F, 7)
	while (put_bits >= 8) EMIT_BYTE()

	state->cur.put_buffer = 0;    /* and reset bit-buffer to empty */
	state->cur.put_bits = 0;
	STORE_BUFFER()

	return TRUE;
}


/* Encode a single block's worth of coefficients */

LOCAL(boolean)
encode_one_block_simd(working_state *state, JCOEFPTR block, int last_dc_val,
                      c_derived_tbl *dctbl, c_derived_tbl *actbl) {
	JOCTET _buffer[BUFSIZE], *buffer;
	size_t bytes, bytestocopy;
	int localbuf = 0;

	LOAD_BUFFER()

	buffer = jsimd_huff_encode_one_block(state, buffer, block, last_dc_val,
	                                     dctbl, actbl);

	STORE_BUFFER()

	return TRUE;
}

LOCAL(boolean)
encode_one_block(working_state *state, JCOEFPTR block, int last_dc_val,
                 c_derived_tbl *dctbl, c_derived_tbl *actbl) {
	int temp, temp2, temp3;
	int nbits;
	int r, code, size;
	JOCTET _buffer[BUFSIZE], *buffer;
	size_t put_buffer;
	int put_bits;
	int code_0xf0 = actbl->ehufco[0xf0], size_0xf0 = actbl->ehufsi[0xf0];
	size_t bytes, bytestocopy;
	int localbuf = 0;

	put_buffer = state->cur.put_buffer;
	put_bits = state->cur.put_bits;
	LOAD_BUFFER()

	/* Encode the DC coefficient difference per section F.1.2.1 */

	temp = temp2 = block[0] - last_dc_val;

	/* This is a well-known technique for obtaining the absolute value without a
	 * branch.  It is derived from an assembly language technique presented in
	 * "How to Optimize for the Pentium Processors", Copyright (c) 1996, 1997 by
	 * Agner Fog.
	 */
	temp3 = temp >> (CHAR_BIT * sizeof(int) - 1);
	temp ^= temp3;
	temp -= temp3;

	/* For a negative input, want temp2 = bitwise complement of abs(input) */
	/* This code assumes we are on a two's complement machine */
	temp2 += temp3;

	/* Find the number of bits needed for the magnitude of the coefficient */
	nbits = JPEG_NBITS(temp);

	/* Emit the Huffman-coded symbol for the number of bits */
	code = dctbl->ehufco[nbits];
	size = dctbl->ehufsi[nbits];
	EMIT_BITS(code, size)

	/* Mask off any extra bits in code */
	temp2 &= (((JLONG) 1) << nbits) - 1;

	/* Emit that number of bits of the value, if positive, */
	/* or the complement of its magnitude, if negative. */
	EMIT_BITS(temp2, nbits)

	/* Encode the AC coefficients per section F.1.2.2 */

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

/* Manually unroll the k loop to eliminate the counter variable.  This
 * improves performance greatly on systems with a limited number of
 * registers (such as x86.)
 */
#define kloop(jpeg_natural_order_of_k) {  \
  if ((temp = block[jpeg_natural_order_of_k]) == 0) { \
    r++; \
  } else { \
    temp2 = temp; \
    /* Branch-less absolute value, bitwise complement, etc., same as above */ \
    temp3 = temp >> (CHAR_BIT * sizeof(int) - 1); \
    temp ^= temp3; \
    temp -= temp3; \
    temp2 += temp3; \
    nbits = JPEG_NBITS_NONZERO(temp); \
    /* if run length > 15, must emit special run-length-16 codes (0xF0) */ \
    while (r > 15) { \
      EMIT_BITS(code_0xf0, size_0xf0) \
      r -= 16; \
    } \
    /* Emit Huffman symbol for run length / number of bits */ \
    temp3 = (r << 4) + nbits;  \
    code = actbl->ehufco[temp3]; \
    size = actbl->ehufsi[temp3]; \
    EMIT_CODE(code, size) \
    r = 0;  \
  } \
}

	/* One iteration for each value in jpeg_natural_order[] */
	kloop(1);
	kloop(8);
	kloop(16);
	kloop(9);
	kloop(2);
	kloop(3);
	kloop(10);
	kloop(17);
	kloop(24);
	kloop(32);
	kloop(25);
	kloop(18);
	kloop(11);
	kloop(4);
	kloop(5);
	kloop(12);
	kloop(19);
	kloop(26);
	kloop(33);
	kloop(40);
	kloop(48);
	kloop(41);
	kloop(34);
	kloop(27);
	kloop(20);
	kloop(13);
	kloop(6);
	kloop(7);
	kloop(14);
	kloop(21);
	kloop(28);
	kloop(35);
	kloop(42);
	kloop(49);
	kloop(56);
	kloop(57);
	kloop(50);
	kloop(43);
	kloop(36);
	kloop(29);
	kloop(22);
	kloop(15);
	kloop(23);
	kloop(30);
	kloop(37);
	kloop(44);
	kloop(51);
	kloop(58);
	kloop(59);
	kloop(52);
	kloop(45);
	kloop(38);
	kloop(31);
	kloop(39);
	kloop(46);
	kloop(53);
	kloop(60);
	kloop(61);
	kloop(54);
	kloop(47);
	kloop(55);
	kloop(62);
	kloop(63);

	/* If the last coef(s) were zero, emit an end-of-block code */
	if (r > 0) {
		code = actbl->ehufco[0];
		size = actbl->ehufsi[0];
		EMIT_BITS(code, size)
	}

	state->cur.put_buffer = put_buffer;
	state->cur.put_bits = put_bits;
	STORE_BUFFER()

	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 */
	if (entropy->simd) {
		for (blkn = 0; blkn < cinfo->blocks_in_MCU; blkn++) {
			ci = cinfo->MCU_membership[blkn];
			compptr = cinfo->cur_comp_info[ci];
			if (!encode_one_block_simd(&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];
		}
	} else {
		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.
 *
 * We first scan the supplied data and count the number of uses of each symbol
 * that is to be Huffman-coded. (This process MUST agree with the code above.)
 * Then we build a Huffman coding tree for the observed counts.
 * Symbols which are not needed at all for the particular image are not
 * assigned any code, which saves space in the DHT marker as well as in
 * the compressed data.
 */

#ifdef ENTROPY_OPT_SUPPORTED


/* Process a single block's worth of coefficients */

LOCAL(void)
htest_one_block(j_compress_ptr cinfo, 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;
	}
	/* Check for out-of-range coefficient values.
	 * Since we're encoding a difference, the range limit is twice as much.
	 */
	if (nbits > MAX_COEF_BITS + 1)
		ERREXIT(cinfo, JERR_BAD_DCT_COEF);

	/* 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++;
			/* Check for out-of-range coefficient values */
			if (nbits > MAX_COEF_BITS)
				ERREXIT(cinfo, JERR_BAD_DCT_COEF);

			/* 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(cinfo, 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 best Huffman code table for the given counts, fill htbl.
 * Note this is also used by jcphuff.c.
 *
 * The JPEG standard requires that no symbol be assigned a codeword of all
 * one bits (so that padding bits added at the end of a compressed segment
 * can't look like a valid code).  Because of the canonical ordering of
 * codewords, this just means that there must be an unused slot in the
 * longest codeword length category.  Section K.2 of the JPEG spec suggests
 * reserving such a slot by pretending that symbol 256 is a valid symbol
 * with count 1.  In theory that's not optimal; giving it count zero but
 * including it in the symbol set anyway should give a better Huffman code.
 * But the theoretically better code actually seems to come out worse in
 * practice, because it produces more all-ones bytes (which incur stuffed
 * zero bytes in the final file).  In any case the difference is tiny.
 *
 * 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 JPEG section K.2.  This method is *not*
 * optimal; it may not choose the best possible limited-length code.  But
 * typically only very-low-frequency symbols will be given less-than-optimal
 * lengths, so the code is almost optimal.  Experimental comparisons against
 * an optimal limited-length-code algorithm indicate that the difference is
 * microscopic --- usually less than a hundredth of a percent of total size.
 * So the extra complexity of an optimal algorithm doesn't seem worthwhile.
 */

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 256 has 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 last 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
	}
}
