The Tor Browser: media/libjpeg/jcarith.c@b8a032363ba2 (annotated)

media/libjpeg/jcarith.c@b8a032363ba2 (annotated)

media/libjpeg/jcarith.c

Thu, 22 Jan 2015 13:21:57 +0100

author: Michael Schloh von Bennewitz <michael@schloh.com>
date: Thu, 22 Jan 2015 13:21:57 +0100
branch: TOR_BUG_9701
changeset 15: b8a032363ba2
permissions: -rw-r--r--

Incorporate requested changes from Mozilla in review:
https://bugzilla.mozilla.org/show_bug.cgi?id=1123480#c6

 /*
  * jcarith.c
  *
  * Developed 1997-2009 by Guido Vollbeding.
  * 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 portable arithmetic entropy encoding routines for JPEG
  * (implementing the ISO/IEC IS 10918-1 and CCITT Recommendation ITU-T T.81).
  *
  * Both sequential and progressive modes are supported in this single module.
  *
  * Suspension is not currently supported in this module.
  */
 #define JPEG_INTERNALS
 #include "jinclude.h"
 #include "jpeglib.h"
 /* Expanded entropy encoder object for arithmetic encoding. */
 typedef struct {
   struct jpeg_entropy_encoder pub; /* public fields */
   INT32 c; /* C register, base of coding interval, layout as in sec. D.1.3 */
   INT32 a;               /* A register, normalized size of coding interval */
   INT32 sc;        /* counter for stacked 0xFF values which might overflow */
   INT32 zc;          /* counter for pending 0x00 output values which might *
                           * be discarded at the end ("Pacman" termination) */
   int ct;  /* bit shift counter, determines when next byte will be written */
   int buffer;                /* buffer for most recent output byte != 0xFF */
   int last_dc_val[MAX_COMPS_IN_SCAN]; /* last DC coef for each component */
   int dc_context[MAX_COMPS_IN_SCAN]; /* context index for DC conditioning */
   unsigned int restarts_to_go;	/* MCUs left in this restart interval */
   int next_restart_num;		/* next restart number to write (0-7) */
   /* Pointers to statistics areas (these workspaces have image lifespan) */
   unsigned char * dc_stats[NUM_ARITH_TBLS];
   unsigned char * ac_stats[NUM_ARITH_TBLS];
   /* Statistics bin for coding with fixed probability 0.5 */
   unsigned char fixed_bin[4];
 } arith_entropy_encoder;
 typedef arith_entropy_encoder * arith_entropy_ptr;
 /* The following two definitions specify the allocation chunk size
  * for the statistics area.
  * According to sections F.1.4.4.1.3 and F.1.4.4.2, we need at least
  * 49 statistics bins for DC, and 245 statistics bins for AC coding.
  *
  * We use a compact representation with 1 byte per statistics bin,
  * thus the numbers directly represent byte sizes.
  * This 1 byte per statistics bin contains the meaning of the MPS
  * (more probable symbol) in the highest bit (mask 0x80), and the
  * index into the probability estimation state machine table
  * in the lower bits (mask 0x7F).
  */
 #define DC_STAT_BINS 64
 #define AC_STAT_BINS 256
 /* NOTE: Uncomment the following #define if you want to use the
  * given formula for calculating the AC conditioning parameter Kx
  * for spectral selection progressive coding in section G.1.3.2
  * of the spec (Kx = Kmin + SRL (8 + Se - Kmin) 4).
  * Although the spec and P&M authors claim that this "has proven
  * to give good results for 8 bit precision samples", I'm not
  * convinced yet that this is really beneficial.
  * Early tests gave only very marginal compression enhancements
  * (a few - around 5 or so - bytes even for very large files),
  * which would turn out rather negative if we'd suppress the
  * DAC (Define Arithmetic Conditioning) marker segments for
  * the default parameters in the future.
  * Note that currently the marker writing module emits 12-byte
  * DAC segments for a full-component scan in a color image.
  * This is not worth worrying about IMHO. However, since the
  * spec defines the default values to be used if the tables
  * are omitted (unlike Huffman tables, which are required
  * anyway), one might optimize this behaviour in the future,
  * and then it would be disadvantageous to use custom tables if
  * they don't provide sufficient gain to exceed the DAC size.
  *
  * On the other hand, I'd consider it as a reasonable result
  * that the conditioning has no significant influence on the
  * compression performance. This means that the basic
  * statistical model is already rather stable.
  *
  * Thus, at the moment, we use the default conditioning values
  * anyway, and do not use the custom formula.
  *
 #define CALCULATE_SPECTRAL_CONDITIONING
  */
 /* 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
 LOCAL(void)
 emit_byte (int val, j_compress_ptr cinfo)
 /* Write next output byte; we do not support suspension in this module. */
 {
   struct jpeg_destination_mgr * dest = cinfo->dest;
   *dest->next_output_byte++ = (JOCTET) val;
   if (--dest->free_in_buffer == 0)
     if (! (*dest->empty_output_buffer) (cinfo))
       ERREXIT(cinfo, JERR_CANT_SUSPEND);
 }
 /*
  * Finish up at the end of an arithmetic-compressed scan.
  */
 METHODDEF(void)
 finish_pass (j_compress_ptr cinfo)
 {
   arith_entropy_ptr e = (arith_entropy_ptr) cinfo->entropy;
   INT32 temp;
   /* Section D.1.8: Termination of encoding */
   /* Find the e->c in the coding interval with the largest
    * number of trailing zero bits */
   if ((temp = (e->a - 1 + e->c) & 0xFFFF0000L) < e->c)
     e->c = temp + 0x8000L;
   else
     e->c = temp;
   /* Send remaining bytes to output */
   e->c <<= e->ct;
   if (e->c & 0xF8000000L) {
     /* One final overflow has to be handled */
     if (e->buffer >= 0) {
       if (e->zc)
 	do emit_byte(0x00, cinfo);
 	while (--e->zc);
       emit_byte(e->buffer + 1, cinfo);
       if (e->buffer + 1 == 0xFF)
 	emit_byte(0x00, cinfo);
     }
     e->zc += e->sc;  /* carry-over converts stacked 0xFF bytes to 0x00 */
     e->sc = 0;
   } else {
     if (e->buffer == 0)
       ++e->zc;
     else if (e->buffer >= 0) {
       if (e->zc)
 	do emit_byte(0x00, cinfo);
 	while (--e->zc);
       emit_byte(e->buffer, cinfo);
     }
     if (e->sc) {
       if (e->zc)
 	do emit_byte(0x00, cinfo);
 	while (--e->zc);
       do {
 	emit_byte(0xFF, cinfo);
 	emit_byte(0x00, cinfo);
       } while (--e->sc);
     }
   }
   /* Output final bytes only if they are not 0x00 */
   if (e->c & 0x7FFF800L) {
     if (e->zc)  /* output final pending zero bytes */
       do emit_byte(0x00, cinfo);
       while (--e->zc);
     emit_byte((e->c >> 19) & 0xFF, cinfo);
     if (((e->c >> 19) & 0xFF) == 0xFF)
       emit_byte(0x00, cinfo);
     if (e->c & 0x7F800L) {
       emit_byte((e->c >> 11) & 0xFF, cinfo);
       if (((e->c >> 11) & 0xFF) == 0xFF)
 	emit_byte(0x00, cinfo);
     }
   }
 }
 /*
  * The core arithmetic encoding routine (common in JPEG and JBIG).
  * This needs to go as fast as possible.
  * Machine-dependent optimization facilities
  * are not utilized in this portable implementation.
  * However, this code should be fairly efficient and
  * may be a good base for further optimizations anyway.
  *
  * Parameter 'val' to be encoded may be 0 or 1 (binary decision).
  *
  * Note: I've added full "Pacman" termination support to the
  * byte output routines, which is equivalent to the optional
  * Discard_final_zeros procedure (Figure D.15) in the spec.
  * Thus, we always produce the shortest possible output
  * stream compliant to the spec (no trailing zero bytes,
  * except for FF stuffing).
  *
  * I've also introduced a new scheme for accessing
  * the probability estimation state machine table,
  * derived from Markus Kuhn's JBIG implementation.
  */
 LOCAL(void)
 arith_encode (j_compress_ptr cinfo, unsigned char *st, int val)
 {
   register arith_entropy_ptr e = (arith_entropy_ptr) cinfo->entropy;
   register unsigned char nl, nm;
   register INT32 qe, temp;
   register int sv;
   /* Fetch values from our compact representation of Table D.2:
    * Qe values and probability estimation state machine
    */
   sv = *st;
   qe = jpeg_aritab[sv & 0x7F];	/* => Qe_Value */
   nl = qe & 0xFF; qe >>= 8;	/* Next_Index_LPS + Switch_MPS */
   nm = qe & 0xFF; qe >>= 8;	/* Next_Index_MPS */
   /* Encode & estimation procedures per sections D.1.4 & D.1.5 */
   e->a -= qe;
   if (val != (sv >> 7)) {
     /* Encode the less probable symbol */
     if (e->a >= qe) {
       /* If the interval size (qe) for the less probable symbol (LPS)
        * is larger than the interval size for the MPS, then exchange
        * the two symbols for coding efficiency, otherwise code the LPS
        * as usual: */
       e->c += e->a;
       e->a = qe;
     }
     *st = (sv & 0x80) ^ nl;	/* Estimate_after_LPS */
   } else {
     /* Encode the more probable symbol */
     if (e->a >= 0x8000L)
       return;  /* A >= 0x8000 -> ready, no renormalization required */
     if (e->a < qe) {
       /* If the interval size (qe) for the less probable symbol (LPS)
        * is larger than the interval size for the MPS, then exchange
        * the two symbols for coding efficiency: */
       e->c += e->a;
       e->a = qe;
     }
     *st = (sv & 0x80) ^ nm;	/* Estimate_after_MPS */
   }
   /* Renormalization & data output per section D.1.6 */
   do {
     e->a <<= 1;
     e->c <<= 1;
     if (--e->ct == 0) {
       /* Another byte is ready for output */
       temp = e->c >> 19;
       if (temp > 0xFF) {
 	/* Handle overflow over all stacked 0xFF bytes */
 	if (e->buffer >= 0) {
 	  if (e->zc)
 	    do emit_byte(0x00, cinfo);
 	    while (--e->zc);
 	  emit_byte(e->buffer + 1, cinfo);
 	  if (e->buffer + 1 == 0xFF)
 	    emit_byte(0x00, cinfo);
 	}
 	e->zc += e->sc;  /* carry-over converts stacked 0xFF bytes to 0x00 */
 	e->sc = 0;
 	/* Note: The 3 spacer bits in the C register guarantee
 	 * that the new buffer byte can't be 0xFF here
 	 * (see page 160 in the P&M JPEG book). */
 	e->buffer = temp & 0xFF;  /* new output byte, might overflow later */
       } else if (temp == 0xFF) {
 	++e->sc;  /* stack 0xFF byte (which might overflow later) */
       } else {
 	/* Output all stacked 0xFF bytes, they will not overflow any more */
 	if (e->buffer == 0)
 	  ++e->zc;
 	else if (e->buffer >= 0) {
 	  if (e->zc)
 	    do emit_byte(0x00, cinfo);
 	    while (--e->zc);
 	  emit_byte(e->buffer, cinfo);
 	}
 	if (e->sc) {
 	  if (e->zc)
 	    do emit_byte(0x00, cinfo);
 	    while (--e->zc);
 	  do {
 	    emit_byte(0xFF, cinfo);
 	    emit_byte(0x00, cinfo);
 	  } while (--e->sc);
 	}
 	e->buffer = temp & 0xFF;  /* new output byte (can still overflow) */
       }
       e->c &= 0x7FFFFL;
       e->ct += 8;
     }
   } while (e->a < 0x8000L);
 }
 /*
  * Emit a restart marker & resynchronize predictions.
  */
 LOCAL(void)
 emit_restart (j_compress_ptr cinfo, int restart_num)
 {
   arith_entropy_ptr entropy = (arith_entropy_ptr) cinfo->entropy;
   int ci;
   jpeg_component_info * compptr;
   finish_pass(cinfo);
   emit_byte(0xFF, cinfo);
   emit_byte(JPEG_RST0 + restart_num, cinfo);
   /* Re-initialize statistics areas */
   for (ci = 0; ci < cinfo->comps_in_scan; ci++) {
     compptr = cinfo->cur_comp_info[ci];
     /* DC needs no table for refinement scan */
     if (cinfo->progressive_mode == 0 || (cinfo->Ss == 0 && cinfo->Ah == 0)) {
       MEMZERO(entropy->dc_stats[compptr->dc_tbl_no], DC_STAT_BINS);
       /* Reset DC predictions to 0 */
       entropy->last_dc_val[ci] = 0;
       entropy->dc_context[ci] = 0;
     }
     /* AC needs no table when not present */
     if (cinfo->progressive_mode == 0 || cinfo->Se) {
       MEMZERO(entropy->ac_stats[compptr->ac_tbl_no], AC_STAT_BINS);
     }
   }
   /* Reset arithmetic encoding variables */
   entropy->c = 0;
   entropy->a = 0x10000L;
   entropy->sc = 0;
   entropy->zc = 0;
   entropy->ct = 11;
   entropy->buffer = -1;  /* empty */
 }
 /*
  * 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)
 {
   arith_entropy_ptr entropy = (arith_entropy_ptr) cinfo->entropy;
   JBLOCKROW block;
   unsigned char *st;
   int blkn, ci, tbl;
   int v, v2, m;
   ISHIFT_TEMPS
   /* Emit restart marker if needed */
   if (cinfo->restart_interval) {
     if (entropy->restarts_to_go == 0) {
       emit_restart(cinfo, entropy->next_restart_num);
       entropy->restarts_to_go = cinfo->restart_interval;
       entropy->next_restart_num++;
       entropy->next_restart_num &= 7;
     }
     entropy->restarts_to_go--;
   }
   /* Encode the MCU data blocks */
   for (blkn = 0; blkn < cinfo->blocks_in_MCU; blkn++) {
     block = MCU_data[blkn];
     ci = cinfo->MCU_membership[blkn];
     tbl = cinfo->cur_comp_info[ci]->dc_tbl_no;
     /* Compute the DC value after the required point transform by Al.
      * This is simply an arithmetic right shift.
      */
     m = IRIGHT_SHIFT((int) ((*block)[0]), cinfo->Al);
     /* Sections F.1.4.1 & F.1.4.4.1: Encoding of DC coefficients */
     /* Table F.4: Point to statistics bin S0 for DC coefficient coding */
     st = entropy->dc_stats[tbl] + entropy->dc_context[ci];
     /* Figure F.4: Encode_DC_DIFF */
     if ((v = m - entropy->last_dc_val[ci]) == 0) {
       arith_encode(cinfo, st, 0);
       entropy->dc_context[ci] = 0;	/* zero diff category */
     } else {
       entropy->last_dc_val[ci] = m;
       arith_encode(cinfo, st, 1);
       /* Figure F.6: Encoding nonzero value v */
       /* Figure F.7: Encoding the sign of v */
       if (v > 0) {
 	arith_encode(cinfo, st + 1, 0);	/* Table F.4: SS = S0 + 1 */
 	st += 2;			/* Table F.4: SP = S0 + 2 */
 	entropy->dc_context[ci] = 4;	/* small positive diff category */
       } else {
 	v = -v;
 	arith_encode(cinfo, st + 1, 1);	/* Table F.4: SS = S0 + 1 */
 	st += 3;			/* Table F.4: SN = S0 + 3 */
 	entropy->dc_context[ci] = 8;	/* small negative diff category */
       }
       /* Figure F.8: Encoding the magnitude category of v */
       m = 0;
       if (v -= 1) {
 	arith_encode(cinfo, st, 1);
 	m = 1;
 	v2 = v;
 	st = entropy->dc_stats[tbl] + 20; /* Table F.4: X1 = 20 */
 	while (v2 >>= 1) {
 	  arith_encode(cinfo, st, 1);
 	  m <<= 1;
 	  st += 1;
 	}
       }
       arith_encode(cinfo, st, 0);
       /* Section F.1.4.4.1.2: Establish dc_context conditioning category */
       if (m < (int) ((1L << cinfo->arith_dc_L[tbl]) >> 1))
 	entropy->dc_context[ci] = 0;	/* zero diff category */
       else if (m > (int) ((1L << cinfo->arith_dc_U[tbl]) >> 1))
 	entropy->dc_context[ci] += 8;	/* large diff category */
       /* Figure F.9: Encoding the magnitude bit pattern of v */
       st += 14;
       while (m >>= 1)
 	arith_encode(cinfo, st, (m & v) ? 1 : 0);
     }
   }
   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)
 {
   arith_entropy_ptr entropy = (arith_entropy_ptr) cinfo->entropy;
   JBLOCKROW block;
   unsigned char *st;
   int tbl, k, ke;
   int v, v2, m;
   /* Emit restart marker if needed */
   if (cinfo->restart_interval) {
     if (entropy->restarts_to_go == 0) {
       emit_restart(cinfo, entropy->next_restart_num);
       entropy->restarts_to_go = cinfo->restart_interval;
       entropy->next_restart_num++;
       entropy->next_restart_num &= 7;
     }
     entropy->restarts_to_go--;
   }
   /* Encode the MCU data block */
   block = MCU_data[0];
   tbl = cinfo->cur_comp_info[0]->ac_tbl_no;
   /* Sections F.1.4.2 & F.1.4.4.2: Encoding of AC coefficients */
   /* Establish EOB (end-of-block) index */
   for (ke = cinfo->Se; ke > 0; ke--)
     /* 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 ((v = (*block)[jpeg_natural_order[ke]]) >= 0) {
       if (v >>= cinfo->Al) break;
     } else {
       v = -v;
       if (v >>= cinfo->Al) break;
     }
   /* Figure F.5: Encode_AC_Coefficients */
   for (k = cinfo->Ss; k <= ke; k++) {
     st = entropy->ac_stats[tbl] + 3 * (k - 1);
     arith_encode(cinfo, st, 0);		/* EOB decision */
     for (;;) {
       if ((v = (*block)[jpeg_natural_order[k]]) >= 0) {
 	if (v >>= cinfo->Al) {
 	  arith_encode(cinfo, st + 1, 1);
 	  arith_encode(cinfo, entropy->fixed_bin, 0);
 	  break;
 	}
       } else {
 	v = -v;
 	if (v >>= cinfo->Al) {
 	  arith_encode(cinfo, st + 1, 1);
 	  arith_encode(cinfo, entropy->fixed_bin, 1);
 	  break;
 	}
       }
       arith_encode(cinfo, st + 1, 0); st += 3; k++;
     }
     st += 2;
     /* Figure F.8: Encoding the magnitude category of v */
     m = 0;
     if (v -= 1) {
       arith_encode(cinfo, st, 1);
       m = 1;
       v2 = v;
       if (v2 >>= 1) {
 	arith_encode(cinfo, st, 1);
 	m <<= 1;
 	st = entropy->ac_stats[tbl] +
 	     (k <= cinfo->arith_ac_K[tbl] ? 189 : 217);
 	while (v2 >>= 1) {
 	  arith_encode(cinfo, st, 1);
 	  m <<= 1;
 	  st += 1;
 	}
       }
     }
     arith_encode(cinfo, st, 0);
     /* Figure F.9: Encoding the magnitude bit pattern of v */
     st += 14;
     while (m >>= 1)
       arith_encode(cinfo, st, (m & v) ? 1 : 0);
   }
   /* Encode EOB decision only if k <= cinfo->Se */
   if (k <= cinfo->Se) {
     st = entropy->ac_stats[tbl] + 3 * (k - 1);
     arith_encode(cinfo, st, 1);
   }
   return TRUE;
 }
 /*
  * MCU encoding for DC successive approximation refinement scan.
  */
 METHODDEF(boolean)
 encode_mcu_DC_refine (j_compress_ptr cinfo, JBLOCKROW *MCU_data)
 {
   arith_entropy_ptr entropy = (arith_entropy_ptr) cinfo->entropy;
   unsigned char *st;
   int Al, blkn;
   /* Emit restart marker if needed */
   if (cinfo->restart_interval) {
     if (entropy->restarts_to_go == 0) {
       emit_restart(cinfo, entropy->next_restart_num);
       entropy->restarts_to_go = cinfo->restart_interval;
       entropy->next_restart_num++;
       entropy->next_restart_num &= 7;
     }
     entropy->restarts_to_go--;
   }
   st = entropy->fixed_bin;	/* use fixed probability estimation */
   Al = cinfo->Al;
   /* Encode the MCU data blocks */
   for (blkn = 0; blkn < cinfo->blocks_in_MCU; blkn++) {
     /* We simply emit the Al'th bit of the DC coefficient value. */
     arith_encode(cinfo, st, (MCU_data[blkn][0][0] >> Al) & 1);
   }
   return TRUE;
 }
 /*
  * MCU encoding for AC successive approximation refinement scan.
  */
 METHODDEF(boolean)
 encode_mcu_AC_refine (j_compress_ptr cinfo, JBLOCKROW *MCU_data)
 {
   arith_entropy_ptr entropy = (arith_entropy_ptr) cinfo->entropy;
   JBLOCKROW block;
   unsigned char *st;
   int tbl, k, ke, kex;
   int v;
   /* Emit restart marker if needed */
   if (cinfo->restart_interval) {
     if (entropy->restarts_to_go == 0) {
       emit_restart(cinfo, entropy->next_restart_num);
       entropy->restarts_to_go = cinfo->restart_interval;
       entropy->next_restart_num++;
       entropy->next_restart_num &= 7;
     }
     entropy->restarts_to_go--;
   }
   /* Encode the MCU data block */
   block = MCU_data[0];
   tbl = cinfo->cur_comp_info[0]->ac_tbl_no;
   /* Section G.1.3.3: Encoding of AC coefficients */
   /* Establish EOB (end-of-block) index */
   for (ke = cinfo->Se; ke > 0; ke--)
     /* 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 ((v = (*block)[jpeg_natural_order[ke]]) >= 0) {
       if (v >>= cinfo->Al) break;
     } else {
       v = -v;
       if (v >>= cinfo->Al) break;
     }
   /* Establish EOBx (previous stage end-of-block) index */
   for (kex = ke; kex > 0; kex--)
     if ((v = (*block)[jpeg_natural_order[kex]]) >= 0) {
       if (v >>= cinfo->Ah) break;
     } else {
       v = -v;
       if (v >>= cinfo->Ah) break;
     }
   /* Figure G.10: Encode_AC_Coefficients_SA */
   for (k = cinfo->Ss; k <= ke; k++) {
     st = entropy->ac_stats[tbl] + 3 * (k - 1);
     if (k > kex)
       arith_encode(cinfo, st, 0);	/* EOB decision */
     for (;;) {
       if ((v = (*block)[jpeg_natural_order[k]]) >= 0) {
 	if (v >>= cinfo->Al) {
 	  if (v >> 1)			/* previously nonzero coef */
 	    arith_encode(cinfo, st + 2, (v & 1));
 	  else {			/* newly nonzero coef */
 	    arith_encode(cinfo, st + 1, 1);
 	    arith_encode(cinfo, entropy->fixed_bin, 0);
 	  }
 	  break;
 	}
       } else {
 	v = -v;
 	if (v >>= cinfo->Al) {
 	  if (v >> 1)			/* previously nonzero coef */
 	    arith_encode(cinfo, st + 2, (v & 1));
 	  else {			/* newly nonzero coef */
 	    arith_encode(cinfo, st + 1, 1);
 	    arith_encode(cinfo, entropy->fixed_bin, 1);
 	  }
 	  break;
 	}
       }
       arith_encode(cinfo, st + 1, 0); st += 3; k++;
     }
   }
   /* Encode EOB decision only if k <= cinfo->Se */
   if (k <= cinfo->Se) {
     st = entropy->ac_stats[tbl] + 3 * (k - 1);
     arith_encode(cinfo, st, 1);
   }
   return TRUE;
 }
 /*
  * Encode and output one MCU's worth of arithmetic-compressed coefficients.
  */
 METHODDEF(boolean)
 encode_mcu (j_compress_ptr cinfo, JBLOCKROW *MCU_data)
 {
   arith_entropy_ptr entropy = (arith_entropy_ptr) cinfo->entropy;
   jpeg_component_info * compptr;
   JBLOCKROW block;
   unsigned char *st;
   int blkn, ci, tbl, k, ke;
   int v, v2, m;
   /* Emit restart marker if needed */
   if (cinfo->restart_interval) {
     if (entropy->restarts_to_go == 0) {
       emit_restart(cinfo, entropy->next_restart_num);
       entropy->restarts_to_go = cinfo->restart_interval;
       entropy->next_restart_num++;
       entropy->next_restart_num &= 7;
     }
     entropy->restarts_to_go--;
   }
   /* 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];
     /* Sections F.1.4.1 & F.1.4.4.1: Encoding of DC coefficients */
     tbl = compptr->dc_tbl_no;
     /* Table F.4: Point to statistics bin S0 for DC coefficient coding */
     st = entropy->dc_stats[tbl] + entropy->dc_context[ci];
     /* Figure F.4: Encode_DC_DIFF */
     if ((v = (*block)[0] - entropy->last_dc_val[ci]) == 0) {
       arith_encode(cinfo, st, 0);
       entropy->dc_context[ci] = 0;	/* zero diff category */
     } else {
       entropy->last_dc_val[ci] = (*block)[0];
       arith_encode(cinfo, st, 1);
       /* Figure F.6: Encoding nonzero value v */
       /* Figure F.7: Encoding the sign of v */
       if (v > 0) {
 	arith_encode(cinfo, st + 1, 0);	/* Table F.4: SS = S0 + 1 */
 	st += 2;			/* Table F.4: SP = S0 + 2 */
 	entropy->dc_context[ci] = 4;	/* small positive diff category */
       } else {
 	v = -v;
 	arith_encode(cinfo, st + 1, 1);	/* Table F.4: SS = S0 + 1 */
 	st += 3;			/* Table F.4: SN = S0 + 3 */
 	entropy->dc_context[ci] = 8;	/* small negative diff category */
       }
       /* Figure F.8: Encoding the magnitude category of v */
       m = 0;
       if (v -= 1) {
 	arith_encode(cinfo, st, 1);
 	m = 1;
 	v2 = v;
 	st = entropy->dc_stats[tbl] + 20; /* Table F.4: X1 = 20 */
 	while (v2 >>= 1) {
 	  arith_encode(cinfo, st, 1);
 	  m <<= 1;
 	  st += 1;
 	}
       }
       arith_encode(cinfo, st, 0);
       /* Section F.1.4.4.1.2: Establish dc_context conditioning category */
       if (m < (int) ((1L << cinfo->arith_dc_L[tbl]) >> 1))
 	entropy->dc_context[ci] = 0;	/* zero diff category */
       else if (m > (int) ((1L << cinfo->arith_dc_U[tbl]) >> 1))
 	entropy->dc_context[ci] += 8;	/* large diff category */
       /* Figure F.9: Encoding the magnitude bit pattern of v */
       st += 14;
       while (m >>= 1)
 	arith_encode(cinfo, st, (m & v) ? 1 : 0);
     }
     /* Sections F.1.4.2 & F.1.4.4.2: Encoding of AC coefficients */
     tbl = compptr->ac_tbl_no;
     /* Establish EOB (end-of-block) index */
     for (ke = DCTSIZE2 - 1; ke > 0; ke--)
       if ((*block)[jpeg_natural_order[ke]]) break;
     /* Figure F.5: Encode_AC_Coefficients */
     for (k = 1; k <= ke; k++) {
       st = entropy->ac_stats[tbl] + 3 * (k - 1);
       arith_encode(cinfo, st, 0);	/* EOB decision */
       while ((v = (*block)[jpeg_natural_order[k]]) == 0) {
 	arith_encode(cinfo, st + 1, 0); st += 3; k++;
       }
       arith_encode(cinfo, st + 1, 1);
       /* Figure F.6: Encoding nonzero value v */
       /* Figure F.7: Encoding the sign of v */
       if (v > 0) {
 	arith_encode(cinfo, entropy->fixed_bin, 0);
       } else {
 	v = -v;
 	arith_encode(cinfo, entropy->fixed_bin, 1);
       }
       st += 2;
       /* Figure F.8: Encoding the magnitude category of v */
       m = 0;
       if (v -= 1) {
 	arith_encode(cinfo, st, 1);
 	m = 1;
 	v2 = v;
 	if (v2 >>= 1) {
 	  arith_encode(cinfo, st, 1);
 	  m <<= 1;
 	  st = entropy->ac_stats[tbl] +
 	       (k <= cinfo->arith_ac_K[tbl] ? 189 : 217);
 	  while (v2 >>= 1) {
 	    arith_encode(cinfo, st, 1);
 	    m <<= 1;
 	    st += 1;
 	  }
 	}
       }
       arith_encode(cinfo, st, 0);
       /* Figure F.9: Encoding the magnitude bit pattern of v */
       st += 14;
       while (m >>= 1)
 	arith_encode(cinfo, st, (m & v) ? 1 : 0);
     }
     /* Encode EOB decision only if k <= DCTSIZE2 - 1 */
     if (k <= DCTSIZE2 - 1) {
       st = entropy->ac_stats[tbl] + 3 * (k - 1);
       arith_encode(cinfo, st, 1);
     }
   }
   return TRUE;
 }
 /*
  * Initialize for an arithmetic-compressed scan.
  */
 METHODDEF(void)
 start_pass (j_compress_ptr cinfo, boolean gather_statistics)
 {
   arith_entropy_ptr entropy = (arith_entropy_ptr) cinfo->entropy;
   int ci, tbl;
   jpeg_component_info * compptr;
   if (gather_statistics)
     /* Make sure to avoid that in the master control logic!
      * We are fully adaptive here and need no extra
      * statistics gathering pass!
      */
     ERREXIT(cinfo, JERR_NOT_COMPILED);
   /* We assume jcmaster.c already validated the progressive scan parameters. */
   /* Select execution routines */
   if (cinfo->progressive_mode) {
     if (cinfo->Ah == 0) {
       if (cinfo->Ss == 0)
 	entropy->pub.encode_mcu = encode_mcu_DC_first;
       else
 	entropy->pub.encode_mcu = encode_mcu_AC_first;
     } else {
       if (cinfo->Ss == 0)
 	entropy->pub.encode_mcu = encode_mcu_DC_refine;
       else
 	entropy->pub.encode_mcu = encode_mcu_AC_refine;
     }
   } else
     entropy->pub.encode_mcu = encode_mcu;
   /* Allocate & initialize requested statistics areas */
   for (ci = 0; ci < cinfo->comps_in_scan; ci++) {
     compptr = cinfo->cur_comp_info[ci];
     /* DC needs no table for refinement scan */
     if (cinfo->progressive_mode == 0 || (cinfo->Ss == 0 && cinfo->Ah == 0)) {
       tbl = compptr->dc_tbl_no;
       if (tbl < 0 || tbl >= NUM_ARITH_TBLS)
 	ERREXIT1(cinfo, JERR_NO_ARITH_TABLE, tbl);
       if (entropy->dc_stats[tbl] == NULL)
 	entropy->dc_stats[tbl] = (unsigned char *) (*cinfo->mem->alloc_small)
 	  ((j_common_ptr) cinfo, JPOOL_IMAGE, DC_STAT_BINS);
       MEMZERO(entropy->dc_stats[tbl], DC_STAT_BINS);
       /* Initialize DC predictions to 0 */
       entropy->last_dc_val[ci] = 0;
       entropy->dc_context[ci] = 0;
     }
     /* AC needs no table when not present */
     if (cinfo->progressive_mode == 0 || cinfo->Se) {
       tbl = compptr->ac_tbl_no;
       if (tbl < 0 || tbl >= NUM_ARITH_TBLS)
 	ERREXIT1(cinfo, JERR_NO_ARITH_TABLE, tbl);
       if (entropy->ac_stats[tbl] == NULL)
 	entropy->ac_stats[tbl] = (unsigned char *) (*cinfo->mem->alloc_small)
 	  ((j_common_ptr) cinfo, JPOOL_IMAGE, AC_STAT_BINS);
       MEMZERO(entropy->ac_stats[tbl], AC_STAT_BINS);
 #ifdef CALCULATE_SPECTRAL_CONDITIONING
       if (cinfo->progressive_mode)
 	/* Section G.1.3.2: Set appropriate arithmetic conditioning value Kx */
 	cinfo->arith_ac_K[tbl] = cinfo->Ss + ((8 + cinfo->Se - cinfo->Ss) >> 4);
 #endif
     }
   }
   /* Initialize arithmetic encoding variables */
   entropy->c = 0;
   entropy->a = 0x10000L;
   entropy->sc = 0;
   entropy->zc = 0;
   entropy->ct = 11;
   entropy->buffer = -1;  /* empty */
   /* Initialize restart stuff */
   entropy->restarts_to_go = cinfo->restart_interval;
   entropy->next_restart_num = 0;
 }
 /*
  * Module initialization routine for arithmetic entropy encoding.
  */
 GLOBAL(void)
 jinit_arith_encoder (j_compress_ptr cinfo)
 {
   arith_entropy_ptr entropy;
   int i;
   entropy = (arith_entropy_ptr)
     (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
 				SIZEOF(arith_entropy_encoder));
   cinfo->entropy = (struct jpeg_entropy_encoder *) entropy;
   entropy->pub.start_pass = start_pass;
   entropy->pub.finish_pass = finish_pass;
   /* Mark tables unallocated */
   for (i = 0; i < NUM_ARITH_TBLS; i++) {
     entropy->dc_stats[i] = NULL;
     entropy->ac_stats[i] = NULL;
   }
   /* Initialize index for fixed probability estimation */
   entropy->fixed_bin[0] = 113;
 }

The Tor Browser / annotate

media/libjpeg/jcarith.c@b8a032363ba2 (annotated)

media/libjpeg/jcarith.c