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ntk/jpeg/jdarith.c

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  1. /*

  2.  * jdarith.c

  3.  *

  4.  * Developed 1997-2009 by Guido Vollbeding.

  5.  * This file is part of the Independent JPEG Group's software.

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

  7.  *

  8.  * This file contains portable arithmetic entropy decoding routines for JPEG

  9.  * (implementing the ISO/IEC IS 10918-1 and CCITT Recommendation ITU-T T.81).

  10.  *

  11.  * Both sequential and progressive modes are supported in this single module.

  12.  *

  13.  * Suspension is not currently supported in this module.

  14.  */

  15. 

  16. #define JPEG_INTERNALS

  17. #include "jinclude.h"

  18. #include "jpeglib.h"

  19. 

  20. 

  21. /* Expanded entropy decoder object for arithmetic decoding. */

  22. 

  23. typedef struct {

  24.   struct jpeg_entropy_decoder pub; /* public fields */

  25. 

  26.   INT32 c;       /* C register, base of coding interval + input bit buffer */

  27.   INT32 a;               /* A register, normalized size of coding interval */

  28.   int ct;     /* bit shift counter, # of bits left in bit buffer part of C */

  29.                                                          /* init: ct = -16 */

  30.                                                          /* run: ct = 0..7 */

  31.                                                          /* error: ct = -1 */

  32.   int last_dc_val[MAX_COMPS_IN_SCAN]; /* last DC coef for each component */

  33.   int dc_context[MAX_COMPS_IN_SCAN]; /* context index for DC conditioning */

  34. 

  35.   unsigned int restarts_to_go;	/* MCUs left in this restart interval */

  36. 

  37.   /* Pointers to statistics areas (these workspaces have image lifespan) */

  38.   unsigned char * dc_stats[NUM_ARITH_TBLS];

  39.   unsigned char * ac_stats[NUM_ARITH_TBLS];

  40. 

  41.   /* Statistics bin for coding with fixed probability 0.5 */

  42.   unsigned char fixed_bin[4];

  43. } arith_entropy_decoder;

  44. 

  45. typedef arith_entropy_decoder * arith_entropy_ptr;

  46. 

  47. /* The following two definitions specify the allocation chunk size

  48.  * for the statistics area.

  49.  * According to sections F.1.4.4.1.3 and F.1.4.4.2, we need at least

  50.  * 49 statistics bins for DC, and 245 statistics bins for AC coding.

  51.  *

  52.  * We use a compact representation with 1 byte per statistics bin,

  53.  * thus the numbers directly represent byte sizes.

  54.  * This 1 byte per statistics bin contains the meaning of the MPS

  55.  * (more probable symbol) in the highest bit (mask 0x80), and the

  56.  * index into the probability estimation state machine table

  57.  * in the lower bits (mask 0x7F).

  58.  */

  59. 

  60. #define DC_STAT_BINS 64

  61. #define AC_STAT_BINS 256

  62. 

  63. 

  64. LOCAL(int)

  65. get_byte (j_decompress_ptr cinfo)

  66. /* Read next input byte; we do not support suspension in this module. */

  67. {

  68.   struct jpeg_source_mgr * src = cinfo->src;

  69. 

  70.   if (src->bytes_in_buffer == 0)

  71.     if (! (*src->fill_input_buffer) (cinfo))

  72.       ERREXIT(cinfo, JERR_CANT_SUSPEND);

  73.   src->bytes_in_buffer--;

  74.   return GETJOCTET(*src->next_input_byte++);

  75. }

  76. 

  77. 

  78. /*

  79.  * The core arithmetic decoding routine (common in JPEG and JBIG).

  80.  * This needs to go as fast as possible.

  81.  * Machine-dependent optimization facilities

  82.  * are not utilized in this portable implementation.

  83.  * However, this code should be fairly efficient and

  84.  * may be a good base for further optimizations anyway.

  85.  *

  86.  * Return value is 0 or 1 (binary decision).

  87.  *

  88.  * Note: I've changed the handling of the code base & bit

  89.  * buffer register C compared to other implementations

  90.  * based on the standards layout & procedures.

  91.  * While it also contains both the actual base of the

  92.  * coding interval (16 bits) and the next-bits buffer,

  93.  * the cut-point between these two parts is floating

  94.  * (instead of fixed) with the bit shift counter CT.

  95.  * Thus, we also need only one (variable instead of

  96.  * fixed size) shift for the LPS/MPS decision, and

  97.  * we can get away with any renormalization update

  98.  * of C (except for new data insertion, of course).

  99.  *

  100.  * I've also introduced a new scheme for accessing

  101.  * the probability estimation state machine table,

  102.  * derived from Markus Kuhn's JBIG implementation.

  103.  */

  104. 

  105. LOCAL(int)

  106. arith_decode (j_decompress_ptr cinfo, unsigned char *st)

  107. {

  108.   register arith_entropy_ptr e = (arith_entropy_ptr) cinfo->entropy;

  109.   register unsigned char nl, nm;

  110.   register INT32 qe, temp;

  111.   register int sv, data;

  112. 

  113.   /* Renormalization & data input per section D.2.6 */

  114.   while (e->a < 0x8000L) {

  115.     if (--e->ct < 0) {

  116.       /* Need to fetch next data byte */

  117.       if (cinfo->unread_marker)

  118. 	data = 0;		/* stuff zero data */

  119.       else {

  120. 	data = get_byte(cinfo);	/* read next input byte */

  121. 	if (data == 0xFF) {	/* zero stuff or marker code */

  122. 	  do data = get_byte(cinfo);

  123. 	  while (data == 0xFF);	/* swallow extra 0xFF bytes */

  124. 	  if (data == 0)

  125. 	    data = 0xFF;	/* discard stuffed zero byte */

  126. 	  else {

  127. 	    /* Note: Different from the Huffman decoder, hitting

  128. 	     * a marker while processing the compressed data

  129. 	     * segment is legal in arithmetic coding.

  130. 	     * The convention is to supply zero data

  131. 	     * then until decoding is complete.

  132. 	     */

  133. 	    cinfo->unread_marker = data;

  134. 	    data = 0;

  135. 	  }

  136. 	}

  137.       }

  138.       e->c = (e->c << 8) | data; /* insert data into C register */

  139.       if ((e->ct += 8) < 0)	 /* update bit shift counter */

  140. 	/* Need more initial bytes */

  141. 	if (++e->ct == 0)

  142. 	  /* Got 2 initial bytes -> re-init A and exit loop */

  143. 	  e->a = 0x8000L; /* => e->a = 0x10000L after loop exit */

  144.     }

  145.     e->a <<= 1;

  146.   }

  147. 

  148.   /* Fetch values from our compact representation of Table D.2:

  149.    * Qe values and probability estimation state machine

  150.    */

  151.   sv = *st;

  152.   qe = jpeg_aritab[sv & 0x7F];	/* => Qe_Value */

  153.   nl = qe & 0xFF; qe >>= 8;	/* Next_Index_LPS + Switch_MPS */

  154.   nm = qe & 0xFF; qe >>= 8;	/* Next_Index_MPS */

  155. 

  156.   /* Decode & estimation procedures per sections D.2.4 & D.2.5 */

  157.   temp = e->a - qe;

  158.   e->a = temp;

  159.   temp <<= e->ct;

  160.   if (e->c >= temp) {

  161.     e->c -= temp;

  162.     /* Conditional LPS (less probable symbol) exchange */

  163.     if (e->a < qe) {

  164.       e->a = qe;

  165.       *st = (sv & 0x80) ^ nm;	/* Estimate_after_MPS */

  166.     } else {

  167.       e->a = qe;

  168.       *st = (sv & 0x80) ^ nl;	/* Estimate_after_LPS */

  169.       sv ^= 0x80;		/* Exchange LPS/MPS */

  170.     }

  171.   } else if (e->a < 0x8000L) {

  172.     /* Conditional MPS (more probable symbol) exchange */

  173.     if (e->a < qe) {

  174.       *st = (sv & 0x80) ^ nl;	/* Estimate_after_LPS */

  175.       sv ^= 0x80;		/* Exchange LPS/MPS */

  176.     } else {

  177.       *st = (sv & 0x80) ^ nm;	/* Estimate_after_MPS */

  178.     }

  179.   }

  180. 

  181.   return sv >> 7;

  182. }

  183. 

  184. 

  185. /*

  186.  * Check for a restart marker & resynchronize decoder.

  187.  */

  188. 

  189. LOCAL(void)

  190. process_restart (j_decompress_ptr cinfo)

  191. {

  192.   arith_entropy_ptr entropy = (arith_entropy_ptr) cinfo->entropy;

  193.   int ci;

  194.   jpeg_component_info * compptr;

  195. 

  196.   /* Advance past the RSTn marker */

  197.   if (! (*cinfo->marker->read_restart_marker) (cinfo))

  198.     ERREXIT(cinfo, JERR_CANT_SUSPEND);

  199. 

  200.   /* Re-initialize statistics areas */

  201.   for (ci = 0; ci < cinfo->comps_in_scan; ci++) {

  202.     compptr = cinfo->cur_comp_info[ci];

  203.     if (! cinfo->progressive_mode || (cinfo->Ss == 0 && cinfo->Ah == 0)) {

  204.       MEMZERO(entropy->dc_stats[compptr->dc_tbl_no], DC_STAT_BINS);

  205.       /* Reset DC predictions to 0 */

  206.       entropy->last_dc_val[ci] = 0;

  207.       entropy->dc_context[ci] = 0;

  208.     }

  209.     if ((! cinfo->progressive_mode && cinfo->lim_Se) ||

  210. 	(cinfo->progressive_mode && cinfo->Ss)) {

  211.       MEMZERO(entropy->ac_stats[compptr->ac_tbl_no], AC_STAT_BINS);

  212.     }

  213.   }

  214. 

  215.   /* Reset arithmetic decoding variables */

  216.   entropy->c = 0;

  217.   entropy->a = 0;

  218.   entropy->ct = -16;	/* force reading 2 initial bytes to fill C */

  219. 

  220.   /* Reset restart counter */

  221.   entropy->restarts_to_go = cinfo->restart_interval;

  222. }

  223. 

  224. 

  225. /*

  226.  * Arithmetic MCU decoding.

  227.  * Each of these routines decodes and returns one MCU's worth of

  228.  * arithmetic-compressed coefficients.

  229.  * The coefficients are reordered from zigzag order into natural array order,

  230.  * but are not dequantized.

  231.  *

  232.  * The i'th block of the MCU is stored into the block pointed to by

  233.  * MCU_data[i].  WE ASSUME THIS AREA IS INITIALLY ZEROED BY THE CALLER.

  234.  */

  235. 

  236. /*

  237.  * MCU decoding for DC initial scan (either spectral selection,

  238.  * or first pass of successive approximation).

  239.  */

  240. 

  241. METHODDEF(boolean)

  242. decode_mcu_DC_first (j_decompress_ptr cinfo, JBLOCKROW *MCU_data)

  243. {

  244.   arith_entropy_ptr entropy = (arith_entropy_ptr) cinfo->entropy;

  245.   JBLOCKROW block;

  246.   unsigned char *st;

  247.   int blkn, ci, tbl, sign;

  248.   int v, m;

  249. 

  250.   /* Process restart marker if needed */

  251.   if (cinfo->restart_interval) {

  252.     if (entropy->restarts_to_go == 0)

  253.       process_restart(cinfo);

  254.     entropy->restarts_to_go--;

  255.   }

  256. 

  257.   if (entropy->ct == -1) return TRUE;	/* if error do nothing */

  258. 

  259.   /* Outer loop handles each block in the MCU */

  260. 

  261.   for (blkn = 0; blkn < cinfo->blocks_in_MCU; blkn++) {

  262.     block = MCU_data[blkn];

  263.     ci = cinfo->MCU_membership[blkn];

  264.     tbl = cinfo->cur_comp_info[ci]->dc_tbl_no;

  265. 

  266.     /* Sections F.2.4.1 & F.1.4.4.1: Decoding of DC coefficients */

  267. 

  268.     /* Table F.4: Point to statistics bin S0 for DC coefficient coding */

  269.     st = entropy->dc_stats[tbl] + entropy->dc_context[ci];

  270. 

  271.     /* Figure F.19: Decode_DC_DIFF */

  272.     if (arith_decode(cinfo, st) == 0)

  273.       entropy->dc_context[ci] = 0;

  274.     else {

  275.       /* Figure F.21: Decoding nonzero value v */

  276.       /* Figure F.22: Decoding the sign of v */

  277.       sign = arith_decode(cinfo, st + 1);

  278.       st += 2; st += sign;

  279.       /* Figure F.23: Decoding the magnitude category of v */

  280.       if ((m = arith_decode(cinfo, st)) != 0) {

  281. 	st = entropy->dc_stats[tbl] + 20;	/* Table F.4: X1 = 20 */

  282. 	while (arith_decode(cinfo, st)) {

  283. 	  if ((m <<= 1) == 0x8000) {

  284. 	    WARNMS(cinfo, JWRN_ARITH_BAD_CODE);

  285. 	    entropy->ct = -1;			/* magnitude overflow */

  286. 	    return TRUE;

  287. 	  }

  288. 	  st += 1;

  289. 	}

  290.       }

  291.       /* Section F.1.4.4.1.2: Establish dc_context conditioning category */

  292.       if (m < (int) ((1L << cinfo->arith_dc_L[tbl]) >> 1))

  293. 	entropy->dc_context[ci] = 0;		   /* zero diff category */

  294.       else if (m > (int) ((1L << cinfo->arith_dc_U[tbl]) >> 1))

  295. 	entropy->dc_context[ci] = 12 + (sign * 4); /* large diff category */

  296.       else

  297. 	entropy->dc_context[ci] = 4 + (sign * 4);  /* small diff category */

  298.       v = m;

  299.       /* Figure F.24: Decoding the magnitude bit pattern of v */

  300.       st += 14;

  301.       while (m >>= 1)

  302. 	if (arith_decode(cinfo, st)) v |= m;

  303.       v += 1; if (sign) v = -v;

  304.       entropy->last_dc_val[ci] += v;

  305.     }

  306. 

  307.     /* Scale and output the DC coefficient (assumes jpeg_natural_order[0]=0) */

  308.     (*block)[0] = (JCOEF) (entropy->last_dc_val[ci] << cinfo->Al);

  309.   }

  310. 

  311.   return TRUE;

  312. }

  313. 

  314. 

  315. /*

  316.  * MCU decoding for AC initial scan (either spectral selection,

  317.  * or first pass of successive approximation).

  318.  */

  319. 

  320. METHODDEF(boolean)

  321. decode_mcu_AC_first (j_decompress_ptr cinfo, JBLOCKROW *MCU_data)

  322. {

  323.   arith_entropy_ptr entropy = (arith_entropy_ptr) cinfo->entropy;

  324.   JBLOCKROW block;

  325.   unsigned char *st;

  326.   int tbl, sign, k;

  327.   int v, m;

  328.   const int * natural_order;

  329. 

  330.   /* Process restart marker if needed */

  331.   if (cinfo->restart_interval) {

  332.     if (entropy->restarts_to_go == 0)

  333.       process_restart(cinfo);

  334.     entropy->restarts_to_go--;

  335.   }

  336. 

  337.   if (entropy->ct == -1) return TRUE;	/* if error do nothing */

  338. 

  339.   natural_order = cinfo->natural_order;

  340. 

  341.   /* There is always only one block per MCU */

  342.   block = MCU_data[0];

  343.   tbl = cinfo->cur_comp_info[0]->ac_tbl_no;

  344. 

  345.   /* Sections F.2.4.2 & F.1.4.4.2: Decoding of AC coefficients */

  346. 

  347.   /* Figure F.20: Decode_AC_coefficients */

  348.   for (k = cinfo->Ss; k <= cinfo->Se; k++) {

  349.     st = entropy->ac_stats[tbl] + 3 * (k - 1);

  350.     if (arith_decode(cinfo, st)) break;		/* EOB flag */

  351.     while (arith_decode(cinfo, st + 1) == 0) {

  352.       st += 3; k++;

  353.       if (k > cinfo->Se) {

  354. 	WARNMS(cinfo, JWRN_ARITH_BAD_CODE);

  355. 	entropy->ct = -1;			/* spectral overflow */

  356. 	return TRUE;

  357.       }

  358.     }

  359.     /* Figure F.21: Decoding nonzero value v */

  360.     /* Figure F.22: Decoding the sign of v */

  361.     sign = arith_decode(cinfo, entropy->fixed_bin);

  362.     st += 2;

  363.     /* Figure F.23: Decoding the magnitude category of v */

  364.     if ((m = arith_decode(cinfo, st)) != 0) {

  365.       if (arith_decode(cinfo, st)) {

  366. 	m <<= 1;

  367. 	st = entropy->ac_stats[tbl] +

  368. 	     (k <= cinfo->arith_ac_K[tbl] ? 189 : 217);

  369. 	while (arith_decode(cinfo, st)) {

  370. 	  if ((m <<= 1) == 0x8000) {

  371. 	    WARNMS(cinfo, JWRN_ARITH_BAD_CODE);

  372. 	    entropy->ct = -1;			/* magnitude overflow */

  373. 	    return TRUE;

  374. 	  }

  375. 	  st += 1;

  376. 	}

  377.       }

  378.     }

  379.     v = m;

  380.     /* Figure F.24: Decoding the magnitude bit pattern of v */

  381.     st += 14;

  382.     while (m >>= 1)

  383.       if (arith_decode(cinfo, st)) v |= m;

  384.     v += 1; if (sign) v = -v;

  385.     /* Scale and output coefficient in natural (dezigzagged) order */

  386.     (*block)[natural_order[k]] = (JCOEF) (v << cinfo->Al);

  387.   }

  388. 

  389.   return TRUE;

  390. }

  391. 

  392. 

  393. /*

  394.  * MCU decoding for DC successive approximation refinement scan.

  395.  */

  396. 

  397. METHODDEF(boolean)

  398. decode_mcu_DC_refine (j_decompress_ptr cinfo, JBLOCKROW *MCU_data)

  399. {

  400.   arith_entropy_ptr entropy = (arith_entropy_ptr) cinfo->entropy;

  401.   unsigned char *st;

  402.   int p1, blkn;

  403. 

  404.   /* Process restart marker if needed */

  405.   if (cinfo->restart_interval) {

  406.     if (entropy->restarts_to_go == 0)

  407.       process_restart(cinfo);

  408.     entropy->restarts_to_go--;

  409.   }

  410. 

  411.   st = entropy->fixed_bin;	/* use fixed probability estimation */

  412.   p1 = 1 << cinfo->Al;		/* 1 in the bit position being coded */

  413. 

  414.   /* Outer loop handles each block in the MCU */

  415. 

  416.   for (blkn = 0; blkn < cinfo->blocks_in_MCU; blkn++) {

  417.     /* Encoded data is simply the next bit of the two's-complement DC value */

  418.     if (arith_decode(cinfo, st))

  419.       MCU_data[blkn][0][0] |= p1;

  420.   }

  421. 

  422.   return TRUE;

  423. }

  424. 

  425. 

  426. /*

  427.  * MCU decoding for AC successive approximation refinement scan.

  428.  */

  429. 

  430. METHODDEF(boolean)

  431. decode_mcu_AC_refine (j_decompress_ptr cinfo, JBLOCKROW *MCU_data)

  432. {

  433.   arith_entropy_ptr entropy = (arith_entropy_ptr) cinfo->entropy;

  434.   JBLOCKROW block;

  435.   JCOEFPTR thiscoef;

  436.   unsigned char *st;

  437.   int tbl, k, kex;

  438.   int p1, m1;

  439.   const int * natural_order;

  440. 

  441.   /* Process restart marker if needed */

  442.   if (cinfo->restart_interval) {

  443.     if (entropy->restarts_to_go == 0)

  444.       process_restart(cinfo);

  445.     entropy->restarts_to_go--;

  446.   }

  447. 

  448.   if (entropy->ct == -1) return TRUE;	/* if error do nothing */

  449. 

  450.   natural_order = cinfo->natural_order;

  451. 

  452.   /* There is always only one block per MCU */

  453.   block = MCU_data[0];

  454.   tbl = cinfo->cur_comp_info[0]->ac_tbl_no;

  455. 

  456.   p1 = 1 << cinfo->Al;		/* 1 in the bit position being coded */

  457.   m1 = (-1) << cinfo->Al;	/* -1 in the bit position being coded */

  458. 

  459.   /* Establish EOBx (previous stage end-of-block) index */

  460.   for (kex = cinfo->Se; kex > 0; kex--)

  461.     if ((*block)[natural_order[kex]]) break;

  462. 

  463.   for (k = cinfo->Ss; k <= cinfo->Se; k++) {

  464.     st = entropy->ac_stats[tbl] + 3 * (k - 1);

  465.     if (k > kex)

  466.       if (arith_decode(cinfo, st)) break;	/* EOB flag */

  467.     for (;;) {

  468.       thiscoef = *block + natural_order[k];

  469.       if (*thiscoef) {				/* previously nonzero coef */

  470. 	if (arith_decode(cinfo, st + 2)) {

  471. 	  if (*thiscoef < 0)

  472. 	    *thiscoef += m1;

  473. 	  else

  474. 	    *thiscoef += p1;

  475. 	}

  476. 	break;

  477.       }

  478.       if (arith_decode(cinfo, st + 1)) {	/* newly nonzero coef */

  479. 	if (arith_decode(cinfo, entropy->fixed_bin))

  480. 	  *thiscoef = m1;

  481. 	else

  482. 	  *thiscoef = p1;

  483. 	break;

  484.       }

  485.       st += 3; k++;

  486.       if (k > cinfo->Se) {

  487. 	WARNMS(cinfo, JWRN_ARITH_BAD_CODE);

  488. 	entropy->ct = -1;			/* spectral overflow */

  489. 	return TRUE;

  490.       }

  491.     }

  492.   }

  493. 

  494.   return TRUE;

  495. }

  496. 

  497. 

  498. /*

  499.  * Decode one MCU's worth of arithmetic-compressed coefficients.

  500.  */

  501. 

  502. METHODDEF(boolean)

  503. decode_mcu (j_decompress_ptr cinfo, JBLOCKROW *MCU_data)

  504. {

  505.   arith_entropy_ptr entropy = (arith_entropy_ptr) cinfo->entropy;

  506.   jpeg_component_info * compptr;

  507.   JBLOCKROW block;

  508.   unsigned char *st;

  509.   int blkn, ci, tbl, sign, k;

  510.   int v, m;

  511.   const int * natural_order;

  512. 

  513.   /* Process restart marker if needed */

  514.   if (cinfo->restart_interval) {

  515.     if (entropy->restarts_to_go == 0)

  516.       process_restart(cinfo);

  517.     entropy->restarts_to_go--;

  518.   }

  519. 

  520.   if (entropy->ct == -1) return TRUE;	/* if error do nothing */

  521. 

  522.   natural_order = cinfo->natural_order;

  523. 

  524.   /* Outer loop handles each block in the MCU */

  525. 

  526.   for (blkn = 0; blkn < cinfo->blocks_in_MCU; blkn++) {

  527.     block = MCU_data[blkn];

  528.     ci = cinfo->MCU_membership[blkn];

  529.     compptr = cinfo->cur_comp_info[ci];

  530. 

  531.     /* Sections F.2.4.1 & F.1.4.4.1: Decoding of DC coefficients */

  532. 

  533.     tbl = compptr->dc_tbl_no;

  534. 

  535.     /* Table F.4: Point to statistics bin S0 for DC coefficient coding */

  536.     st = entropy->dc_stats[tbl] + entropy->dc_context[ci];

  537. 

  538.     /* Figure F.19: Decode_DC_DIFF */

  539.     if (arith_decode(cinfo, st) == 0)

  540.       entropy->dc_context[ci] = 0;

  541.     else {

  542.       /* Figure F.21: Decoding nonzero value v */

  543.       /* Figure F.22: Decoding the sign of v */

  544.       sign = arith_decode(cinfo, st + 1);

  545.       st += 2; st += sign;

  546.       /* Figure F.23: Decoding the magnitude category of v */

  547.       if ((m = arith_decode(cinfo, st)) != 0) {

  548. 	st = entropy->dc_stats[tbl] + 20;	/* Table F.4: X1 = 20 */

  549. 	while (arith_decode(cinfo, st)) {

  550. 	  if ((m <<= 1) == 0x8000) {

  551. 	    WARNMS(cinfo, JWRN_ARITH_BAD_CODE);

  552. 	    entropy->ct = -1;			/* magnitude overflow */

  553. 	    return TRUE;

  554. 	  }

  555. 	  st += 1;

  556. 	}

  557.       }

  558.       /* Section F.1.4.4.1.2: Establish dc_context conditioning category */

  559.       if (m < (int) ((1L << cinfo->arith_dc_L[tbl]) >> 1))

  560. 	entropy->dc_context[ci] = 0;		   /* zero diff category */

  561.       else if (m > (int) ((1L << cinfo->arith_dc_U[tbl]) >> 1))

  562. 	entropy->dc_context[ci] = 12 + (sign * 4); /* large diff category */

  563.       else

  564. 	entropy->dc_context[ci] = 4 + (sign * 4);  /* small diff category */

  565.       v = m;

  566.       /* Figure F.24: Decoding the magnitude bit pattern of v */

  567.       st += 14;

  568.       while (m >>= 1)

  569. 	if (arith_decode(cinfo, st)) v |= m;

  570.       v += 1; if (sign) v = -v;

  571.       entropy->last_dc_val[ci] += v;

  572.     }

  573. 

  574.     (*block)[0] = (JCOEF) entropy->last_dc_val[ci];

  575. 

  576.     /* Sections F.2.4.2 & F.1.4.4.2: Decoding of AC coefficients */

  577. 

  578.     tbl = compptr->ac_tbl_no;

  579. 

  580.     /* Figure F.20: Decode_AC_coefficients */

  581.     for (k = 1; k <= cinfo->lim_Se; k++) {

  582.       st = entropy->ac_stats[tbl] + 3 * (k - 1);

  583.       if (arith_decode(cinfo, st)) break;	/* EOB flag */

  584.       while (arith_decode(cinfo, st + 1) == 0) {

  585. 	st += 3; k++;

  586. 	if (k > cinfo->lim_Se) {

  587. 	  WARNMS(cinfo, JWRN_ARITH_BAD_CODE);

  588. 	  entropy->ct = -1;			/* spectral overflow */

  589. 	  return TRUE;

  590. 	}

  591.       }

  592.       /* Figure F.21: Decoding nonzero value v */

  593.       /* Figure F.22: Decoding the sign of v */

  594.       sign = arith_decode(cinfo, entropy->fixed_bin);

  595.       st += 2;

  596.       /* Figure F.23: Decoding the magnitude category of v */

  597.       if ((m = arith_decode(cinfo, st)) != 0) {

  598. 	if (arith_decode(cinfo, st)) {

  599. 	  m <<= 1;

  600. 	  st = entropy->ac_stats[tbl] +

  601. 	       (k <= cinfo->arith_ac_K[tbl] ? 189 : 217);

  602. 	  while (arith_decode(cinfo, st)) {

  603. 	    if ((m <<= 1) == 0x8000) {

  604. 	      WARNMS(cinfo, JWRN_ARITH_BAD_CODE);

  605. 	      entropy->ct = -1;			/* magnitude overflow */

  606. 	      return TRUE;

  607. 	    }

  608. 	    st += 1;

  609. 	  }

  610. 	}

  611.       }

  612.       v = m;

  613.       /* Figure F.24: Decoding the magnitude bit pattern of v */

  614.       st += 14;

  615.       while (m >>= 1)

  616. 	if (arith_decode(cinfo, st)) v |= m;

  617.       v += 1; if (sign) v = -v;

  618.       (*block)[natural_order[k]] = (JCOEF) v;

  619.     }

  620.   }

  621. 

  622.   return TRUE;

  623. }

  624. 

  625. 

  626. /*

  627.  * Initialize for an arithmetic-compressed scan.

  628.  */

  629. 

  630. METHODDEF(void)

  631. start_pass (j_decompress_ptr cinfo)

  632. {

  633.   arith_entropy_ptr entropy = (arith_entropy_ptr) cinfo->entropy;

  634.   int ci, tbl;

  635.   jpeg_component_info * compptr;

  636. 

  637.   if (cinfo->progressive_mode) {

  638.     /* Validate progressive scan parameters */

  639.     if (cinfo->Ss == 0) {

  640.       if (cinfo->Se != 0)

  641. 	goto bad;

  642.     } else {

  643.       /* need not check Ss/Se < 0 since they came from unsigned bytes */

  644.       if (cinfo->Se < cinfo->Ss || cinfo->Se > cinfo->lim_Se)

  645. 	goto bad;

  646.       /* AC scans may have only one component */

  647.       if (cinfo->comps_in_scan != 1)

  648. 	goto bad;

  649.     }

  650.     if (cinfo->Ah != 0) {

  651.       /* Successive approximation refinement scan: must have Al = Ah-1. */

  652.       if (cinfo->Ah-1 != cinfo->Al)

  653. 	goto bad;

  654.     }

  655.     if (cinfo->Al > 13) {	/* need not check for < 0 */

  656.       bad:

  657.       ERREXIT4(cinfo, JERR_BAD_PROGRESSION,

  658. 	       cinfo->Ss, cinfo->Se, cinfo->Ah, cinfo->Al);

  659.     }

  660.     /* Update progression status, and verify that scan order is legal.

  661.      * Note that inter-scan inconsistencies are treated as warnings

  662.      * not fatal errors ... not clear if this is right way to behave.

  663.      */

  664.     for (ci = 0; ci < cinfo->comps_in_scan; ci++) {

  665.       int coefi, cindex = cinfo->cur_comp_info[ci]->component_index;

  666.       int *coef_bit_ptr = & cinfo->coef_bits[cindex][0];

  667.       if (cinfo->Ss && coef_bit_ptr[0] < 0) /* AC without prior DC scan */

  668. 	WARNMS2(cinfo, JWRN_BOGUS_PROGRESSION, cindex, 0);

  669.       for (coefi = cinfo->Ss; coefi <= cinfo->Se; coefi++) {

  670. 	int expected = (coef_bit_ptr[coefi] < 0) ? 0 : coef_bit_ptr[coefi];

  671. 	if (cinfo->Ah != expected)

  672. 	  WARNMS2(cinfo, JWRN_BOGUS_PROGRESSION, cindex, coefi);

  673. 	coef_bit_ptr[coefi] = cinfo->Al;

  674.       }

  675.     }

  676.     /* Select MCU decoding routine */

  677.     if (cinfo->Ah == 0) {

  678.       if (cinfo->Ss == 0)

  679. 	entropy->pub.decode_mcu = decode_mcu_DC_first;

  680.       else

  681. 	entropy->pub.decode_mcu = decode_mcu_AC_first;

  682.     } else {

  683.       if (cinfo->Ss == 0)

  684. 	entropy->pub.decode_mcu = decode_mcu_DC_refine;

  685.       else

  686. 	entropy->pub.decode_mcu = decode_mcu_AC_refine;

  687.     }

  688.   } else {

  689.     /* Check that the scan parameters Ss, Se, Ah/Al are OK for sequential JPEG.

  690.      * This ought to be an error condition, but we make it a warning.

  691.      */

  692.     if (cinfo->Ss != 0 || cinfo->Ah != 0 || cinfo->Al != 0 ||

  693. 	(cinfo->Se < DCTSIZE2 && cinfo->Se != cinfo->lim_Se))

  694.       WARNMS(cinfo, JWRN_NOT_SEQUENTIAL);

  695.     /* Select MCU decoding routine */

  696.     entropy->pub.decode_mcu = decode_mcu;

  697.   }

  698. 

  699.   /* Allocate & initialize requested statistics areas */

  700.   for (ci = 0; ci < cinfo->comps_in_scan; ci++) {

  701.     compptr = cinfo->cur_comp_info[ci];

  702.     if (! cinfo->progressive_mode || (cinfo->Ss == 0 && cinfo->Ah == 0)) {

  703.       tbl = compptr->dc_tbl_no;

  704.       if (tbl < 0 || tbl >= NUM_ARITH_TBLS)

  705. 	ERREXIT1(cinfo, JERR_NO_ARITH_TABLE, tbl);

  706.       if (entropy->dc_stats[tbl] == NULL)

  707. 	entropy->dc_stats[tbl] = (unsigned char *) (*cinfo->mem->alloc_small)

  708. 	  ((j_common_ptr) cinfo, JPOOL_IMAGE, DC_STAT_BINS);

  709.       MEMZERO(entropy->dc_stats[tbl], DC_STAT_BINS);

  710.       /* Initialize DC predictions to 0 */

  711.       entropy->last_dc_val[ci] = 0;

  712.       entropy->dc_context[ci] = 0;

  713.     }

  714.     if ((! cinfo->progressive_mode && cinfo->lim_Se) ||

  715. 	(cinfo->progressive_mode && cinfo->Ss)) {

  716.       tbl = compptr->ac_tbl_no;

  717.       if (tbl < 0 || tbl >= NUM_ARITH_TBLS)

  718. 	ERREXIT1(cinfo, JERR_NO_ARITH_TABLE, tbl);

  719.       if (entropy->ac_stats[tbl] == NULL)

  720. 	entropy->ac_stats[tbl] = (unsigned char *) (*cinfo->mem->alloc_small)

  721. 	  ((j_common_ptr) cinfo, JPOOL_IMAGE, AC_STAT_BINS);

  722.       MEMZERO(entropy->ac_stats[tbl], AC_STAT_BINS);

  723.     }

  724.   }

  725. 

  726.   /* Initialize arithmetic decoding variables */

  727.   entropy->c = 0;

  728.   entropy->a = 0;

  729.   entropy->ct = -16;	/* force reading 2 initial bytes to fill C */

  730. 

  731.   /* Initialize restart counter */

  732.   entropy->restarts_to_go = cinfo->restart_interval;

  733. }

  734. 

  735. 

  736. /*

  737.  * Module initialization routine for arithmetic entropy decoding.

  738.  */

  739. 

  740. GLOBAL(void)

  741. jinit_arith_decoder (j_decompress_ptr cinfo)

  742. {

  743.   arith_entropy_ptr entropy;

  744.   int i;

  745. 

  746.   entropy = (arith_entropy_ptr)

  747.     (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,

  748. 				SIZEOF(arith_entropy_decoder));

  749.   cinfo->entropy = (struct jpeg_entropy_decoder *) entropy;

  750.   entropy->pub.start_pass = start_pass;

  751. 

  752.   /* Mark tables unallocated */

  753.   for (i = 0; i < NUM_ARITH_TBLS; i++) {

  754.     entropy->dc_stats[i] = NULL;

  755.     entropy->ac_stats[i] = NULL;

  756.   }

  757. 

  758.   /* Initialize index for fixed probability estimation */

  759.   entropy->fixed_bin[0] = 113;

  760. 

  761.   if (cinfo->progressive_mode) {

  762.     /* Create progression status table */

  763.     int *coef_bit_ptr, ci;

  764.     cinfo->coef_bits = (int (*)[DCTSIZE2])

  765.       (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,

  766. 				  cinfo->num_components*DCTSIZE2*SIZEOF(int));

  767.     coef_bit_ptr = & cinfo->coef_bits[0][0];

  768.     for (ci = 0; ci < cinfo->num_components; ci++) 

  769.       for (i = 0; i < DCTSIZE2; i++)

  770. 	*coef_bit_ptr++ = -1;

  771.   }

  772. }