/*

 * jcphuff.c

 *

 * This file was part of the Independent JPEG Group's software:

 * Copyright (C) 1995-1997, Thomas G. Lane.

 * libjpeg-turbo Modifications:

 * Copyright (C) 2011, 2015, 2018, 2021-2022, D. R. Commander.

 * Copyright (C) 2016, 2018, 2022, Matthieu Darbois.

 * For conditions of distribution and use, see the accompanying README.ijg

 * 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 "jsimd.h"

#include "jconfigint.h"

#include <limits.h>

#ifdef HAVE_INTRIN_H

#include <intrin.h>

#ifdef _MSC_VER

#ifdef HAVE_BITSCANFORWARD64

#pragma intrinsic(_BitScanForward64)

#endif

#ifdef HAVE_BITSCANFORWARD

#pragma intrinsic(_BitScanForward)

#endif

#endif

#endif

#ifdef C_PROGRESSIVE_SUPPORTED

/*

 * 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

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

typedef struct {

  struct jpeg_entropy_encoder pub; /* public fields */

  /* Pointer to routine to prepare data for encode_mcu_AC_first() */

  void (*AC_first_prepare) (const JCOEF *block,

                            const int *jpeg_natural_order_start, int Sl,

                            int Al, UJCOEF *values, size_t *zerobits);

  /* Pointer to routine to prepare data for encode_mcu_AC_refine() */

  int (*AC_refine_prepare) (const JCOEF *block,

                            const int *jpeg_natural_order_start, int Sl,

                            int Al, UJCOEF *absvalues, size_t *bits);

  /* 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 */

  size_t 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 JLONG.

 * We assume that int right shift is unsigned if JLONG 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

#define PAD(v, p)  ((v + (p) - 1) & (~((p) - 1)))

/* Forward declarations */

METHODDEF(boolean) encode_mcu_DC_first(j_compress_ptr cinfo,

                                       JBLOCKROW *MCU_data);

METHODDEF(void) encode_mcu_AC_first_prepare

  (const JCOEF *block, const int *jpeg_natural_order_start, int Sl, int Al,

   UJCOEF *values, size_t *zerobits);

METHODDEF(boolean) encode_mcu_AC_first(j_compress_ptr cinfo,

                                       JBLOCKROW *MCU_data);

METHODDEF(boolean) encode_mcu_DC_refine(j_compress_ptr cinfo,

                                        JBLOCKROW *MCU_data);

METHODDEF(int) encode_mcu_AC_refine_prepare

  (const JCOEF *block, const int *jpeg_natural_order_start, int Sl, int Al,

   UJCOEF *absvalues, size_t *bits);

METHODDEF(boolean) encode_mcu_AC_refine(j_compress_ptr cinfo,

                                        JBLOCKROW *MCU_data);

METHODDEF(void) finish_pass_phuff(j_compress_ptr cinfo);

METHODDEF(void) finish_pass_gather_phuff(j_compress_ptr cinfo);

/* Count bit loop zeroes */

INLINE

METHODDEF(int)

count_zeroes(size_t *x)

{

#if defined(HAVE_BUILTIN_CTZL)

  int result;

  result = __builtin_ctzl(*x);

  *x >>= result;

#elif defined(HAVE_BITSCANFORWARD64)

  unsigned long result;

  _BitScanForward64(&result, *x);

  *x >>= result;

#elif defined(HAVE_BITSCANFORWARD)

  unsigned long result;

  _BitScanForward(&result, *x);

  *x >>= result;

#else

  int result = 0;

  while ((*x & 1) == 0) {

    ++result;

    *x >>= 1;

  }

#endif

  return (int)result;

}

/*

 * 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;

    if (jsimd_can_encode_mcu_AC_first_prepare())

      entropy->AC_first_prepare = jsimd_encode_mcu_AC_first_prepare;

    else

      entropy->AC_first_prepare = encode_mcu_AC_first_prepare;

  } else {

    if (is_DC_band)

      entropy->pub.encode_mcu = encode_mcu_DC_refine;

    else {

      entropy->pub.encode_mcu = encode_mcu_AC_refine;

      if (jsimd_can_encode_mcu_AC_refine_prepare())

        entropy->AC_refine_prepare = jsimd_encode_mcu_AC_refine_prepare;

      else

        entropy->AC_refine_prepare = encode_mcu_AC_refine_prepare;

      /* 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;

    /* Get table index */

    if (is_DC_band) {

      if (cinfo->Ah != 0)       /* DC refinement needs no table */

        continue;

      tbl = compptr->dc_tbl_no;

    } else {

      entropy->ac_tbl_no = tbl = compptr->ac_tbl_no;

    }

    if (gather_statistics) {

      /* Check for invalid table index */

      /* (make_c_derived_tbl does this in the other path) */

      if (tbl < 0 || tbl >= NUM_HUFF_TBLS)

        ERREXIT1(cinfo, JERR_NO_HUFF_TABLE, tbl);

      /* 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 table */

      /* We may do this more than once for a table, but it's not expensive */

      jpeg_make_c_derived_tbl(cinfo, is_DC_band, 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.

 */

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 size_t put_buffer = (size_t)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 &= (((size_t)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.

 */

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 = JPEG_NBITS_NONZERO(temp) - 1;

    /* safety check: shouldn't happen given limited correction-bit buffer */

    if (nbits > 14)

      ERREXIT(entropy->cinfo, JERR_HUFF_MISSING_CODE);

    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, temp3;

  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 */

    /* 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;              /* temp is abs value of input */

    /* For a negative input, want temp2 = bitwise complement of abs(input) */

    temp2 = temp ^ temp3;

    /* Find the number of bits needed for the magnitude of the coefficient */

    nbits = JPEG_NBITS(temp);

    /* 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/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;

}

/*

 * Data preparation for encode_mcu_AC_first().

 */

#define COMPUTE_ABSVALUES_AC_FIRST(Sl) { \

  for (k = 0; k < Sl; k++) { \

    temp = block[jpeg_natural_order_start[k]]; \

    if (temp == 0) \

      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). \

     */ \

    temp2 = temp >> (CHAR_BIT * sizeof(int) - 1); \

    temp ^= temp2; \

    temp -= temp2;              /* temp is abs value of input */ \

    temp >>= Al;                /* apply the point transform */ \

    /* Watch out for case that nonzero coef is zero after point transform */ \

    if (temp == 0) \

      continue; \

    /* For a negative coef, want temp2 = bitwise complement of abs(coef) */ \

    temp2 ^= temp; \

    values[k] = (UJCOEF)temp; \

    values[k + DCTSIZE2] = (UJCOEF)temp2; \

    zerobits |= ((size_t)1U) << k; \

  } \

}

METHODDEF(void)

encode_mcu_AC_first_prepare(const JCOEF *block,

                            const int *jpeg_natural_order_start, int Sl,

                            int Al, UJCOEF *values, size_t *bits)

{

  register int k, temp, temp2;

  size_t zerobits = 0U;

  int Sl0 = Sl;

#if SIZEOF_SIZE_T == 4

  if (Sl0 > 32)

    Sl0 = 32;

#endif

  COMPUTE_ABSVALUES_AC_FIRST(Sl0);

  bits[0] = zerobits;

#if SIZEOF_SIZE_T == 4

  zerobits = 0U;

  if (Sl > 32) {

    Sl -= 32;

    jpeg_natural_order_start += 32;

    values += 32;

    COMPUTE_ABSVALUES_AC_FIRST(Sl);

  }

  bits[1] = zerobits;

#endif

}

/*

 * MCU encoding for AC initial scan (either spectral selection,

 * or first pass of successive approximation).

 */

#define ENCODE_COEFS_AC_FIRST(label) { \

  while (zerobits) { \

    r = count_zeroes(&zerobits); \

    cvalue += r; \

label \

    temp  = cvalue[0]; \

    temp2 = cvalue[DCTSIZE2]; \

    \

    /* 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 = JPEG_NBITS_NONZERO(temp);  /* there must be at least one 1 bit */ \

    /* Check for out-of-range coefficient values */ \

    if (nbits > MAX_COEF_BITS) \

      ERREXIT(cinfo, JERR_BAD_DCT_COEF); \

    \

    /* 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); \

    \

    cvalue++; \

    zerobits >>= 1; \

  } \

}

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, r;

  int Sl = cinfo->Se - cinfo->Ss + 1;

  int Al = cinfo->Al;

  UJCOEF values_unaligned[2 * DCTSIZE2 + 15];

  UJCOEF *values;

  const UJCOEF *cvalue;

  size_t zerobits;

  size_t bits[8 / SIZEOF_SIZE_T];

  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);

#ifdef WITH_SIMD

  cvalue = values = (UJCOEF *)PAD((size_t)values_unaligned, 16);

#else

  /* Not using SIMD, so alignment is not needed */

  cvalue = values = values_unaligned;

#endif

  /* Prepare data */

  entropy->AC_first_prepare(MCU_data[0][0], jpeg_natural_order + cinfo->Ss,

                            Sl, Al, values, bits);

  zerobits = bits[0];

#if SIZEOF_SIZE_T == 4

  zerobits |= bits[1];

#endif

  /* Emit any pending EOBRUN */

  if (zerobits && (entropy->EOBRUN > 0))

    emit_eobrun(entropy);

#if SIZEOF_SIZE_T == 4

  zerobits = bits[0];

#endif

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

  ENCODE_COEFS_AC_FIRST((void)0;);

#if SIZEOF_SIZE_T == 4

  zerobits = bits[1];

  if (zerobits) {

    int diff = ((values + DCTSIZE2 / 2) - cvalue);

    r = count_zeroes(&zerobits);

    r += diff;

    cvalue += r;

    goto first_iter_ac_first;

  }

  ENCODE_COEFS_AC_FIRST(first_iter_ac_first:);

#endif

  if (cvalue < (values + Sl)) { /* 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;

}

/*

 * Data preparation for encode_mcu_AC_refine().

 */

#define COMPUTE_ABSVALUES_AC_REFINE(Sl, koffset) { \

  /* It is convenient to make a pre-pass to determine the transformed \

   * coefficients' absolute values and the EOB position. \

   */ \

  for (k = 0; k < Sl; k++) { \

    temp = block[jpeg_natural_order_start[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. \

     */ \

    temp2 = temp >> (CHAR_BIT * sizeof(int) - 1); \

    temp ^= temp2; \

    temp -= temp2;              /* temp is abs value of input */ \

    temp >>= Al;                /* apply the point transform */ \

    if (temp != 0) { \

      zerobits |= ((size_t)1U) << k; \

      signbits |= ((size_t)(temp2 + 1)) << k; \

    } \

    absvalues[k] = (UJCOEF)temp; /* save abs value for main pass */ \

    if (temp == 1) \

      EOB = k + koffset;        /* EOB = index of last newly-nonzero coef */ \

  } \

}

METHODDEF(int)

encode_mcu_AC_refine_prepare(const JCOEF *block,

                             const int *jpeg_natural_order_start, int Sl,

                             int Al, UJCOEF *absvalues, size_t *bits)

{

  register int k, temp, temp2;

  int EOB = 0;

  size_t zerobits = 0U, signbits = 0U;

  int Sl0 = Sl;

#if SIZEOF_SIZE_T == 4

  if (Sl0 > 32)

    Sl0 = 32;

#endif

  COMPUTE_ABSVALUES_AC_REFINE(Sl0, 0);

  bits[0] = zerobits;

#if SIZEOF_SIZE_T == 8

  bits[1] = signbits;

#else

  bits[2] = signbits;

  zerobits = 0U;

  signbits = 0U;

  if (Sl > 32) {

    Sl -= 32;

    jpeg_natural_order_start += 32;

    absvalues += 32;

    COMPUTE_ABSVALUES_AC_REFINE(Sl, 32);

  }

  bits[1] = zerobits;

  bits[3] = signbits;

#endif

  return EOB;

}

/*

 * MCU encoding for AC successive approximation refinement scan.

 */

#define ENCODE_COEFS_AC_REFINE(label) { \

  while (zerobits) { \

    idx = count_zeroes(&zerobits); \

    r += idx; \

    cabsvalue += idx; \

    signbits >>= idx; \

label \

    /* Emit any required ZRLs, but not if they can be folded into EOB */ \

    while (r > 15 && (cabsvalue <= EOBPTR)) { \

      /* 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; \

    } \

    \

    temp = *cabsvalue++; \

    \

    /* 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); \

      signbits >>= 1; \

      zerobits >>= 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 = signbits & 1; /* ((*block)[jpeg_natural_order_start[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 */ \

    signbits >>= 1; \

    zerobits >>= 1; \

  } \

}

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, r, idx;

  char *BR_buffer;

  unsigned int BR;

  int Sl = cinfo->Se - cinfo->Ss + 1;

  int Al = cinfo->Al;

  UJCOEF absvalues_unaligned[DCTSIZE2 + 15];

  UJCOEF *absvalues;

  const UJCOEF *cabsvalue, *EOBPTR;

  size_t zerobits, signbits;

  size_t bits[16 / SIZEOF_SIZE_T];

  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);

#ifdef WITH_SIMD

  cabsvalue = absvalues = (UJCOEF *)PAD((size_t)absvalues_unaligned, 16);

#else

  /* Not using SIMD, so alignment is not needed */

  cabsvalue = absvalues = absvalues_unaligned;

#endif

  /* Prepare data */

  EOBPTR = absvalues +

    entropy->AC_refine_prepare(MCU_data[0][0], jpeg_natural_order + cinfo->Ss,

                               Sl, Al, absvalues, bits);

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

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