/* * jcarith.c * * It can only acomplesh simple arithmetic coding. */#include "commondecls.h"#define RIGHT_SHIFT(x,shft) x>=0 ? x>>shft : -((-x)>>shft)/* 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). *//* 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. * * 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. *//* * Finish up at the end of an arithmetic-compressed scan. */voidflush_bits (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(cinfo,0x00);	while (--e->zc);      emit_byte(cinfo,e->buffer + 1);      if (e->buffer + 1 == 0xFF)	emit_byte(cinfo,0x00);    }    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(cinfo,0x00);	while (--e->zc);      emit_byte(cinfo,e->buffer);    }    if (e->sc) {      if (e->zc)	do emit_byte(cinfo,0x00);	while (--e->zc);      do {	emit_byte(cinfo,0xFF);	emit_byte(cinfo,0x00);      } 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(cinfo,0x00);      while (--e->zc);    emit_byte(cinfo,(e->c >> 19) & 0xFF);    if (((e->c >> 19) & 0xFF) == 0xFF)      emit_byte(cinfo,0x00);    if (e->c & 0x7F800L) {      emit_byte(cinfo,(e->c >> 11) & 0xFF);      if (((e->c >> 11) & 0xFF) == 0xFF)	emit_byte(cinfo,0x00);    }  }}/* * 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. */voidarith_encode (j_compress_ptr cinfo, unsigned char *st, int val) {  extern const INT32 jaritab[];  register arith_entropy_ptr e = 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 = jaritab[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) & (0x00000001))) {    /* 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: ,it is equal to code        * the LPS.*/      e->c += e->a;      e->a = qe;    }    *st = (sv & 0x80) ^ nm ;	/* Estimate_after_MPS ,no change of the sense of the MPS*/  }  /* Renormalization & data output per section D.1.6 */  do {    e->a <<= 1;    e->c <<= 1;    if (--e->ct == 0) {      /* The followning is the byte_out programe.*/      /* Another byte is ready for output */      temp = e->c >> 19;      if (temp > 0xFF) {	/*Handle overflow over all stacked 0xFF bytes */	if (e->buffer >= 0) {	  	   emit_byte(cinfo,e->buffer + 1);	  if (e->buffer + 1 == 0xFF)	  emit_byte(cinfo,0x00); 	}	/*e->zc += e->sc;*/  /* carry-over converts stacked 0xFF bytes to 0x00 and output them*/	while(e->sc-->0)	  emit_byte(cinfo,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) {           emit_byte(cinfo,e->buffer);	   if (e->sc) {	     while (e->sc--) {	       emit_byte(cinfo,0xFF);	       emit_byte(cinfo,0x00);	     } 	    e->sc=0;	    }	           }         e->buffer = temp & 0xFF;  /* new output byte (can still overflow) */      }      e->c &= 0x7FFFFL;      e->ct = 8;    }  } while (e->a < 0x8000L);  }/* * Encode and output one MCU's worth of arithmetic-compressed coefficients. */voidencode_row (j_compress_ptr cinfo,JSAMPROW row,int i){  arith_entropy_ptr entropy = (arith_entropy_ptr) cinfo->entropy;  unsigned char * st;  unsigned char context_a=0;  int num,ci, tbl, k, ke;  int v, v2, m,last_val=0,Rc=0,predic_val;  entropy->context=0;  /* Encode the MCU data blocks */  for (num = 0; num < cinfo->image_width; num++) {        /* 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 + entropy->context*5+entropy->context_b[num];    /*predic_val=last_val+((entropy->val_b[num]-Rc)>>1);*/    /*predic_val=RIGHT_SHIFT(last_val+entropy->val_b[num],1);*/    v=get_errval(cinfo,last_val,entropy->val_b[num],Rc,entropy->val_b[num+1],row+num);    /* if (i==0)       printf("row[%d]:%x  v=%d\n",num,row[num],v);*/    /*v=row[num]-predic_val;*/    /* Figure F.4: Encode_DC_DIFF */    if ((v ) == 0) {      arith_encode(cinfo, st, 0);      entropy->context = 0;	                /* zero diff category */          } else {            arith_encode(cinfo, st, 1);      /* Figure F.6: Encoding nonzero value v */      /* Figure F.7: Encoding the sign of v */      if (v > 0) {	st +=1;	arith_encode(cinfo, st, 0);	/* Table F.4: SS = S0 + 1 */	st += 1;			/* Table F.4: SP = S0 + 2 */	entropy->context = 4;	                /* small positive diff category */      } else {	st +=1;	v = -v;	arith_encode(cinfo, st, 1);	/* Table F.4: SS = S0 + 1 */	st += 2;			/* Table F.4: SN = S0 + 3 */	entropy->context = 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;        if ( entropy->context_b[num]>8 )	  st=entropy->dc_stats+129;	else	  st = entropy->dc_stats + 100; /* Table H.3: X1 = X1_context(Db)*/	    /*st=entropy->dc_stats+20;*/	 while (v2 >>= 1) {	   arith_encode(cinfo, st, 1);	   m <<= 1;	   st += 1;	}      }      arith_encode(cinfo, st, 0);            /* v -=1;       *m=1;       *if (v>m){       *arith_encode(cinfo,st,1);       *if ( entropy->context_b[num]>8 )       *  st=entropy->dc_stats+129;       * else       *  st = entropy->dc_stats + 100; * Table H.3: X1 = X1_context(Db)*       *m=2;       * while (v>=m){	*  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) (((INT32) 1 << cinfo->arith_dc_L) >> 1))	entropy->context = 0;	        /* zero diff category */      else if ((m) > (int) (((INT32) 1 << cinfo->arith_dc_U)>>1 ))	entropy->context += 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);    }    entropy->context_b[num]=entropy->context;    Rc=entropy->val_b[num];    last_val=entropy->val_b[num]=row[num];  }    }