The Tor Browser: comparison media/libjpeg/jdhuff.c

--1:000000000000
+:d8363959993b
+/*
+* jdhuff.c
+*
+* This file was part of the Independent JPEG Group's software:
+* Copyright (C) 1991-1997, Thomas G. Lane.
+* libjpeg-turbo Modifications:
+* Copyright (C) 2009-2011, D. R. Commander.
+* For conditions of distribution and use, see the accompanying README file.
+*
+* This file contains Huffman entropy decoding routines.
+*
+* Much of the complexity here has to do with supporting input suspension.
+* If the data source module demands suspension, we want to be able to back
+* up to the start of the current MCU.  To do this, we copy state variables
+* into local working storage, and update them back to the permanent
+* storage only upon successful completion of an MCU.
+*/
+#define JPEG_INTERNALS
+#include "jinclude.h"
+#include "jpeglib.h"
+#include "jdhuff.h"		/* Declarations shared with jdphuff.c */
+#include "jpegcomp.h"
+#include "jstdhuff.c"
+/*
+* Expanded entropy decoder object for Huffman decoding.
+*
+* The savable_state subrecord contains fields that change within an MCU,
+* but must not be updated permanently until we complete the MCU.
+*/
+typedef struct {
+int last_dc_val[MAX_COMPS_IN_SCAN]; /* last DC coef for each component */
+} savable_state;
+/* This macro is to work around compilers with missing or broken
+* structure assignment.  You'll need to fix this code if you have
+* such a compiler and you change MAX_COMPS_IN_SCAN.
+*/
+#ifndef NO_STRUCT_ASSIGN
+#define ASSIGN_STATE(dest,src)  ((dest) = (src))
+#else
+#if MAX_COMPS_IN_SCAN == 4
+#define ASSIGN_STATE(dest,src)  \
+	((dest).last_dc_val[0] = (src).last_dc_val[0], \
+	 (dest).last_dc_val[1] = (src).last_dc_val[1], \
+	 (dest).last_dc_val[2] = (src).last_dc_val[2], \
+	 (dest).last_dc_val[3] = (src).last_dc_val[3])
+#endif
+#endif
+typedef struct {
+struct jpeg_entropy_decoder pub; /* public fields */
+/* These fields are loaded into local variables at start of each MCU.
+* In case of suspension, we exit WITHOUT updating them.
+*/
+bitread_perm_state bitstate;	/* Bit buffer at start of MCU */
+savable_state saved;		/* Other state at start of MCU */
+/* These fields are NOT loaded into local working state. */
+unsigned int restarts_to_go;	/* MCUs left in this restart interval */
+/* Pointers to derived tables (these workspaces have image lifespan) */
+d_derived_tbl * dc_derived_tbls[NUM_HUFF_TBLS];
+d_derived_tbl * ac_derived_tbls[NUM_HUFF_TBLS];
+/* Precalculated info set up by start_pass for use in decode_mcu: */
+/* Pointers to derived tables to be used for each block within an MCU */
+d_derived_tbl * dc_cur_tbls[D_MAX_BLOCKS_IN_MCU];
+d_derived_tbl * ac_cur_tbls[D_MAX_BLOCKS_IN_MCU];
+/* Whether we care about the DC and AC coefficient values for each block */
+boolean dc_needed[D_MAX_BLOCKS_IN_MCU];
+boolean ac_needed[D_MAX_BLOCKS_IN_MCU];
+} huff_entropy_decoder;
+typedef huff_entropy_decoder * huff_entropy_ptr;
+/*
+* Initialize for a Huffman-compressed scan.
+*/
+METHODDEF(void)
+start_pass_huff_decoder (j_decompress_ptr cinfo)
+{
+huff_entropy_ptr entropy = (huff_entropy_ptr) cinfo->entropy;
+int ci, blkn, dctbl, actbl;
+jpeg_component_info * compptr;
+/* Check that the scan parameters Ss, Se, Ah/Al are OK for sequential JPEG.
+* This ought to be an error condition, but we make it a warning because
+* there are some baseline files out there with all zeroes in these bytes.
+*/
+if (cinfo->Ss != 0 || cinfo->Se != DCTSIZE2-1 ||
+cinfo->Ah != 0 || cinfo->Al != 0)
+WARNMS(cinfo, JWRN_NOT_SEQUENTIAL);
+for (ci = 0; ci < cinfo->comps_in_scan; ci++) {
+compptr = cinfo->cur_comp_info[ci];
+dctbl = compptr->dc_tbl_no;
+actbl = compptr->ac_tbl_no;
+/* Compute derived values for Huffman tables */
+/* We may do this more than once for a table, but it's not expensive */
+jpeg_make_d_derived_tbl(cinfo, TRUE, dctbl,
+			    & entropy->dc_derived_tbls[dctbl]);
+jpeg_make_d_derived_tbl(cinfo, FALSE, actbl,
+			    & entropy->ac_derived_tbls[actbl]);
+/* Initialize DC predictions to 0 */
+entropy->saved.last_dc_val[ci] = 0;
+}
+/* Precalculate decoding info for each block in an MCU of this scan */
+for (blkn = 0; blkn < cinfo->blocks_in_MCU; blkn++) {
+ci = cinfo->MCU_membership[blkn];
+compptr = cinfo->cur_comp_info[ci];
+/* Precalculate which table to use for each block */
+entropy->dc_cur_tbls[blkn] = entropy->dc_derived_tbls[compptr->dc_tbl_no];
+entropy->ac_cur_tbls[blkn] = entropy->ac_derived_tbls[compptr->ac_tbl_no];
+/* Decide whether we really care about the coefficient values */
+if (compptr->component_needed) {
+entropy->dc_needed[blkn] = TRUE;
+/* we don't need the ACs if producing a 1/8th-size image */
+entropy->ac_needed[blkn] = (compptr->_DCT_scaled_size > 1);
+} else {
+entropy->dc_needed[blkn] = entropy->ac_needed[blkn] = FALSE;
+}
+}
+/* Initialize bitread state variables */
+entropy->bitstate.bits_left = 0;
+entropy->bitstate.get_buffer = 0; /* unnecessary, but keeps Purify quiet */
+entropy->pub.insufficient_data = FALSE;
+/* Initialize restart counter */
+entropy->restarts_to_go = cinfo->restart_interval;
+}
+/*
+* Compute the derived values for a Huffman table.
+* This routine also performs some validation checks on the table.
+*
+* Note this is also used by jdphuff.c.
+*/
+GLOBAL(void)
+jpeg_make_d_derived_tbl (j_decompress_ptr cinfo, boolean isDC, int tblno,
+			 d_derived_tbl ** pdtbl)
+{
+JHUFF_TBL *htbl;
+d_derived_tbl *dtbl;
+int p, i, l, si, numsymbols;
+int lookbits, ctr;
+char huffsize[257];
+unsigned int huffcode[257];
+unsigned int code;
+/* Note that huffsize[] and huffcode[] are filled in code-length order,
+* paralleling the order of the symbols themselves in htbl->huffval[].
+*/
+/* Find the input Huffman table */
+if (tblno < 0 || tblno >= NUM_HUFF_TBLS)
+ERREXIT1(cinfo, JERR_NO_HUFF_TABLE, tblno);
+htbl =
+isDC ? cinfo->dc_huff_tbl_ptrs[tblno] : cinfo->ac_huff_tbl_ptrs[tblno];
+if (htbl == NULL)
+ERREXIT1(cinfo, JERR_NO_HUFF_TABLE, tblno);
+/* Allocate a workspace if we haven't already done so. */
+if (*pdtbl == NULL)
+*pdtbl = (d_derived_tbl *)
+(*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
+				  SIZEOF(d_derived_tbl));
+dtbl = *pdtbl;
+dtbl->pub = htbl;		/* fill in back link */
+/* Figure C.1: make table of Huffman code length for each symbol */
+p = 0;
+for (l = 1; l <= 16; l++) {
+i = (int) htbl->bits[l];
+if (i < 0 || p + i > 256)	/* protect against table overrun */
+ERREXIT(cinfo, JERR_BAD_HUFF_TABLE);
+while (i--)
+huffsize[p++] = (char) l;
+}
+huffsize[p] = 0;
+numsymbols = p;
+/* Figure C.2: generate the codes themselves */
+/* We also validate that the counts represent a legal Huffman code tree. */
+code = 0;
+si = huffsize[0];
+p = 0;
+while (huffsize[p]) {
+while (((int) huffsize[p]) == si) {
+huffcode[p++] = code;
+code++;
+}
+/* code is now 1 more than the last code used for codelength si; but
+* it must still fit in si bits, since no code is allowed to be all ones.
+*/
+if (((INT32) code) >= (((INT32) 1) << si))
+ERREXIT(cinfo, JERR_BAD_HUFF_TABLE);
+code <<= 1;
+si++;
+}
+/* Figure F.15: generate decoding tables for bit-sequential decoding */
+p = 0;
+for (l = 1; l <= 16; l++) {
+if (htbl->bits[l]) {
+/* valoffset[l] = huffval[] index of 1st symbol of code length l,
+* minus the minimum code of length l
+*/
+dtbl->valoffset[l] = (INT32) p - (INT32) huffcode[p];
+p += htbl->bits[l];
+dtbl->maxcode[l] = huffcode[p-1]; /* maximum code of length l */
+} else {
+dtbl->maxcode[l] = -1;	/* -1 if no codes of this length */
+}
+}
+dtbl->valoffset[17] = 0;
+dtbl->maxcode[17] = 0xFFFFFL; /* ensures jpeg_huff_decode terminates */
+/* Compute lookahead tables to speed up decoding.
+* First we set all the table entries to 0, indicating "too long";
+* then we iterate through the Huffman codes that are short enough and
+* fill in all the entries that correspond to bit sequences starting
+* with that code.
+*/
+for (i = 0; i < (1 << HUFF_LOOKAHEAD); i++)
+dtbl->lookup[i] = (HUFF_LOOKAHEAD + 1) << HUFF_LOOKAHEAD;
+p = 0;
+for (l = 1; l <= HUFF_LOOKAHEAD; l++) {
+for (i = 1; i <= (int) htbl->bits[l]; i++, p++) {
+/* l = current code's length, p = its index in huffcode[] & huffval[]. */
+/* Generate left-justified code followed by all possible bit sequences */
+lookbits = huffcode[p] << (HUFF_LOOKAHEAD-l);
+for (ctr = 1 << (HUFF_LOOKAHEAD-l); ctr > 0; ctr--) {
+	dtbl->lookup[lookbits] = (l << HUFF_LOOKAHEAD) | htbl->huffval[p];
+	lookbits++;
+}
+}
+}
+/* Validate symbols as being reasonable.
+* For AC tables, we make no check, but accept all byte values 0..255.
+* For DC tables, we require the symbols to be in range 0..15.
+* (Tighter bounds could be applied depending on the data depth and mode,
+* but this is sufficient to ensure safe decoding.)
+*/
+if (isDC) {
+for (i = 0; i < numsymbols; i++) {
+int sym = htbl->huffval[i];
+if (sym < 0 || sym > 15)
+	ERREXIT(cinfo, JERR_BAD_HUFF_TABLE);
+}
+}
+}
+/*
+* Out-of-line code for bit fetching (shared with jdphuff.c).
+* See jdhuff.h for info about usage.
+* Note: current values of get_buffer and bits_left are passed as parameters,
+* but are returned in the corresponding fields of the state struct.
+*
+* On most machines MIN_GET_BITS should be 25 to allow the full 32-bit width
+* of get_buffer to be used.  (On machines with wider words, an even larger
+* buffer could be used.)  However, on some machines 32-bit shifts are
+* quite slow and take time proportional to the number of places shifted.
+* (This is true with most PC compilers, for instance.)  In this case it may
+* be a win to set MIN_GET_BITS to the minimum value of 15.  This reduces the
+* average shift distance at the cost of more calls to jpeg_fill_bit_buffer.
+*/
+#ifdef SLOW_SHIFT_32
+#define MIN_GET_BITS  15	/* minimum allowable value */
+#else
+#define MIN_GET_BITS  (BIT_BUF_SIZE-7)
+#endif
+GLOBAL(boolean)
+jpeg_fill_bit_buffer (bitread_working_state * state,
+		      register bit_buf_type get_buffer, register int bits_left,
+		      int nbits)
+/* Load up the bit buffer to a depth of at least nbits */
+{
+/* Copy heavily used state fields into locals (hopefully registers) */
+register const JOCTET * next_input_byte = state->next_input_byte;
+register size_t bytes_in_buffer = state->bytes_in_buffer;
+j_decompress_ptr cinfo = state->cinfo;
+/* Attempt to load at least MIN_GET_BITS bits into get_buffer. */
+/* (It is assumed that no request will be for more than that many bits.) */
+/* We fail to do so only if we hit a marker or are forced to suspend. */
+if (cinfo->unread_marker == 0) {	/* cannot advance past a marker */
+while (bits_left < MIN_GET_BITS) {
+register int c;
+/* Attempt to read a byte */
+if (bytes_in_buffer == 0) {
+	if (! (*cinfo->src->fill_input_buffer) (cinfo))
+	  return FALSE;
+	next_input_byte = cinfo->src->next_input_byte;
+	bytes_in_buffer = cinfo->src->bytes_in_buffer;
+}
+bytes_in_buffer--;
+c = GETJOCTET(*next_input_byte++);
+/* If it's 0xFF, check and discard stuffed zero byte */
+if (c == 0xFF) {
+	/* Loop here to discard any padding FF's on terminating marker,
+	 * so that we can save a valid unread_marker value.  NOTE: we will
+	 * accept multiple FF's followed by a 0 as meaning a single FF data
+	 * byte.  This data pattern is not valid according to the standard.
+	 */
+	do {
+	  if (bytes_in_buffer == 0) {
+	    if (! (*cinfo->src->fill_input_buffer) (cinfo))
+	      return FALSE;
+	    next_input_byte = cinfo->src->next_input_byte;
+	    bytes_in_buffer = cinfo->src->bytes_in_buffer;
+	  }
+	  bytes_in_buffer--;
+	  c = GETJOCTET(*next_input_byte++);
+	} while (c == 0xFF);
+	if (c == 0) {
+	  /* Found FF/00, which represents an FF data byte */
+	  c = 0xFF;
+	} else {
+	  /* Oops, it's actually a marker indicating end of compressed data.
+	   * Save the marker code for later use.
+	   * Fine point: it might appear that we should save the marker into
+	   * bitread working state, not straight into permanent state.  But
+	   * once we have hit a marker, we cannot need to suspend within the
+	   * current MCU, because we will read no more bytes from the data
+	   * source.  So it is OK to update permanent state right away.
+	   */
+	  cinfo->unread_marker = c;
+	  /* See if we need to insert some fake zero bits. */
+	  goto no_more_bytes;
+	}
+}
+/* OK, load c into get_buffer */
+get_buffer = (get_buffer << 8) | c;
+bits_left += 8;
+} /* end while */
+} else {
+no_more_bytes:
+/* We get here if we've read the marker that terminates the compressed
+* data segment.  There should be enough bits in the buffer register
+* to satisfy the request; if so, no problem.
+*/
+if (nbits > bits_left) {
+/* Uh-oh.  Report corrupted data to user and stuff zeroes into
+* the data stream, so that we can produce some kind of image.
+* We use a nonvolatile flag to ensure that only one warning message
+* appears per data segment.
+*/
+if (! cinfo->entropy->insufficient_data) {
+	WARNMS(cinfo, JWRN_HIT_MARKER);
+	cinfo->entropy->insufficient_data = TRUE;
+}
+/* Fill the buffer with zero bits */
+get_buffer <<= MIN_GET_BITS - bits_left;
+bits_left = MIN_GET_BITS;
+}
+}
+/* Unload the local registers */
+state->next_input_byte = next_input_byte;
+state->bytes_in_buffer = bytes_in_buffer;
+state->get_buffer = get_buffer;
+state->bits_left = bits_left;
+return TRUE;
+}
+/* Macro version of the above, which performs much better but does not
+handle markers.  We have to hand off any blocks with markers to the
+slower routines. */
+#define GET_BYTE \
+{ \
+register int c0, c1; \
+c0 = GETJOCTET(*buffer++); \
+c1 = GETJOCTET(*buffer); \
+/* Pre-execute most common case */ \
+get_buffer = (get_buffer << 8) | c0; \
+bits_left += 8; \
+if (c0 == 0xFF) { \
+/* Pre-execute case of FF/00, which represents an FF data byte */ \
+buffer++; \
+if (c1 != 0) { \
+/* Oops, it's actually a marker indicating end of compressed data. */ \
+cinfo->unread_marker = c1; \
+/* Back out pre-execution and fill the buffer with zero bits */ \
+buffer -= 2; \
+get_buffer &= ~0xFF; \
+} \
+} \
+}
+#if __WORDSIZE == 64 || defined(_WIN64)
+/* Pre-fetch 48 bytes, because the holding register is 64-bit */
+#define FILL_BIT_BUFFER_FAST \
+if (bits_left < 16) { \
+GET_BYTE GET_BYTE GET_BYTE GET_BYTE GET_BYTE GET_BYTE \
+}
+#else
+/* Pre-fetch 16 bytes, because the holding register is 32-bit */
+#define FILL_BIT_BUFFER_FAST \
+if (bits_left < 16) { \
+GET_BYTE GET_BYTE \
+}
+#endif
+/*
+* Out-of-line code for Huffman code decoding.
+* See jdhuff.h for info about usage.
+*/
+GLOBAL(int)
+jpeg_huff_decode (bitread_working_state * state,
+		  register bit_buf_type get_buffer, register int bits_left,
+		  d_derived_tbl * htbl, int min_bits)
+{
+register int l = min_bits;
+register INT32 code;
+/* HUFF_DECODE has determined that the code is at least min_bits */
+/* bits long, so fetch that many bits in one swoop. */
+CHECK_BIT_BUFFER(*state, l, return -1);
+code = GET_BITS(l);
+/* Collect the rest of the Huffman code one bit at a time. */
+/* This is per Figure F.16 in the JPEG spec. */
+while (code > htbl->maxcode[l]) {
+code <<= 1;
+CHECK_BIT_BUFFER(*state, 1, return -1);
+code |= GET_BITS(1);
+l++;
+}
+/* Unload the local registers */
+state->get_buffer = get_buffer;
+state->bits_left = bits_left;
+/* With garbage input we may reach the sentinel value l = 17. */
+if (l > 16) {
+WARNMS(state->cinfo, JWRN_HUFF_BAD_CODE);
+return 0;			/* fake a zero as the safest result */
+}
+return htbl->pub->huffval[ (int) (code + htbl->valoffset[l]) ];
+}
+/*
+* Figure F.12: extend sign bit.
+* On some machines, a shift and add will be faster than a table lookup.
+*/
+#define AVOID_TABLES
+#ifdef AVOID_TABLES
+#define HUFF_EXTEND(x,s)  ((x) + ((((x) - (1<<((s)-1))) >> 31) & (((-1)<<(s)) + 1)))
+#else
+#define HUFF_EXTEND(x,s)  ((x) < extend_test[s] ? (x) + extend_offset[s] : (x))
+static const int extend_test[16] =   /* entry n is 2**(n-1) */
+{ 0, 0x0001, 0x0002, 0x0004, 0x0008, 0x0010, 0x0020, 0x0040, 0x0080,
+0x0100, 0x0200, 0x0400, 0x0800, 0x1000, 0x2000, 0x4000 };
+static const int extend_offset[16] = /* entry n is (-1 << n) + 1 */
+{ 0, ((-1)<<1) + 1, ((-1)<<2) + 1, ((-1)<<3) + 1, ((-1)<<4) + 1,
+((-1)<<5) + 1, ((-1)<<6) + 1, ((-1)<<7) + 1, ((-1)<<8) + 1,
+((-1)<<9) + 1, ((-1)<<10) + 1, ((-1)<<11) + 1, ((-1)<<12) + 1,
+((-1)<<13) + 1, ((-1)<<14) + 1, ((-1)<<15) + 1 };
+#endif /* AVOID_TABLES */
+/*
+* Check for a restart marker & resynchronize decoder.
+* Returns FALSE if must suspend.
+*/
+LOCAL(boolean)
+process_restart (j_decompress_ptr cinfo)
+{
+huff_entropy_ptr entropy = (huff_entropy_ptr) cinfo->entropy;
+int ci;
+/* Throw away any unused bits remaining in bit buffer; */
+/* include any full bytes in next_marker's count of discarded bytes */
+cinfo->marker->discarded_bytes += entropy->bitstate.bits_left / 8;
+entropy->bitstate.bits_left = 0;
+/* Advance past the RSTn marker */
+if (! (*cinfo->marker->read_restart_marker) (cinfo))
+return FALSE;
+/* Re-initialize DC predictions to 0 */
+for (ci = 0; ci < cinfo->comps_in_scan; ci++)
+entropy->saved.last_dc_val[ci] = 0;
+/* Reset restart counter */
+entropy->restarts_to_go = cinfo->restart_interval;
+/* Reset out-of-data flag, unless read_restart_marker left us smack up
+* against a marker.  In that case we will end up treating the next data
+* segment as empty, and we can avoid producing bogus output pixels by
+* leaving the flag set.
+*/
+if (cinfo->unread_marker == 0)
+entropy->pub.insufficient_data = FALSE;
+return TRUE;
+}
+LOCAL(boolean)
+decode_mcu_slow (j_decompress_ptr cinfo, JBLOCKROW *MCU_data)
+{
+huff_entropy_ptr entropy = (huff_entropy_ptr) cinfo->entropy;
+BITREAD_STATE_VARS;
+int blkn;
+savable_state state;
+/* Outer loop handles each block in the MCU */
+/* Load up working state */
+BITREAD_LOAD_STATE(cinfo,entropy->bitstate);
+ASSIGN_STATE(state, entropy->saved);
+for (blkn = 0; blkn < cinfo->blocks_in_MCU; blkn++) {
+JBLOCKROW block = MCU_data[blkn];
+d_derived_tbl * dctbl = entropy->dc_cur_tbls[blkn];
+d_derived_tbl * actbl = entropy->ac_cur_tbls[blkn];
+register int s, k, r;
+/* Decode a single block's worth of coefficients */
+/* Section F.2.2.1: decode the DC coefficient difference */
+HUFF_DECODE(s, br_state, dctbl, return FALSE, label1);
+if (s) {
+CHECK_BIT_BUFFER(br_state, s, return FALSE);
+r = GET_BITS(s);
+s = HUFF_EXTEND(r, s);
+}
+if (entropy->dc_needed[blkn]) {
+/* Convert DC difference to actual value, update last_dc_val */
+int ci = cinfo->MCU_membership[blkn];
+s += state.last_dc_val[ci];
+state.last_dc_val[ci] = s;
+/* Output the DC coefficient (assumes jpeg_natural_order[0] = 0) */
+(*block)[0] = (JCOEF) s;
+}
+if (entropy->ac_needed[blkn]) {
+/* Section F.2.2.2: decode the AC coefficients */
+/* Since zeroes are skipped, output area must be cleared beforehand */
+for (k = 1; k < DCTSIZE2; k++) {
+HUFF_DECODE(s, br_state, actbl, return FALSE, label2);
+r = s >> 4;
+s &= 15;
+if (s) {
+k += r;
+CHECK_BIT_BUFFER(br_state, s, return FALSE);
+r = GET_BITS(s);
+s = HUFF_EXTEND(r, s);
+/* Output coefficient in natural (dezigzagged) order.
+* Note: the extra entries in jpeg_natural_order[] will save us
+* if k >= DCTSIZE2, which could happen if the data is corrupted.
+*/
+(*block)[jpeg_natural_order[k]] = (JCOEF) s;
+} else {
+if (r != 15)
+break;
+k += 15;
+}
+}
+} else {
+/* Section F.2.2.2: decode the AC coefficients */
+/* In this path we just discard the values */
+for (k = 1; k < DCTSIZE2; k++) {
+HUFF_DECODE(s, br_state, actbl, return FALSE, label3);
+r = s >> 4;
+s &= 15;
+if (s) {
+k += r;
+CHECK_BIT_BUFFER(br_state, s, return FALSE);
+DROP_BITS(s);
+} else {
+if (r != 15)
+break;
+k += 15;
+}
+}
+}
+}
+/* Completed MCU, so update state */
+BITREAD_SAVE_STATE(cinfo,entropy->bitstate);
+ASSIGN_STATE(entropy->saved, state);
+return TRUE;
+}
+LOCAL(boolean)
+decode_mcu_fast (j_decompress_ptr cinfo, JBLOCKROW *MCU_data)
+{
+huff_entropy_ptr entropy = (huff_entropy_ptr) cinfo->entropy;
+BITREAD_STATE_VARS;
+JOCTET *buffer;
+int blkn;
+savable_state state;
+/* Outer loop handles each block in the MCU */
+/* Load up working state */
+BITREAD_LOAD_STATE(cinfo,entropy->bitstate);
+buffer = (JOCTET *) br_state.next_input_byte;
+ASSIGN_STATE(state, entropy->saved);
+for (blkn = 0; blkn < cinfo->blocks_in_MCU; blkn++) {
+JBLOCKROW block = MCU_data[blkn];
+d_derived_tbl * dctbl = entropy->dc_cur_tbls[blkn];
+d_derived_tbl * actbl = entropy->ac_cur_tbls[blkn];
+register int s, k, r, l;
+HUFF_DECODE_FAST(s, l, dctbl);
+if (s) {
+FILL_BIT_BUFFER_FAST
+r = GET_BITS(s);
+s = HUFF_EXTEND(r, s);
+}
+if (entropy->dc_needed[blkn]) {
+int ci = cinfo->MCU_membership[blkn];
+s += state.last_dc_val[ci];
+state.last_dc_val[ci] = s;
+(*block)[0] = (JCOEF) s;
+}
+if (entropy->ac_needed[blkn]) {
+for (k = 1; k < DCTSIZE2; k++) {
+HUFF_DECODE_FAST(s, l, actbl);
+r = s >> 4;
+s &= 15;
+if (s) {
+k += r;
+FILL_BIT_BUFFER_FAST
+r = GET_BITS(s);
+s = HUFF_EXTEND(r, s);
+(*block)[jpeg_natural_order[k]] = (JCOEF) s;
+} else {
+if (r != 15) break;
+k += 15;
+}
+}
+} else {
+for (k = 1; k < DCTSIZE2; k++) {
+HUFF_DECODE_FAST(s, l, actbl);
+r = s >> 4;
+s &= 15;
+if (s) {
+k += r;
+FILL_BIT_BUFFER_FAST
+DROP_BITS(s);
+} else {
+if (r != 15) break;
+k += 15;
+}
+}
+}
+}
+if (cinfo->unread_marker != 0) {
+cinfo->unread_marker = 0;
+return FALSE;
+}
+br_state.bytes_in_buffer -= (buffer - br_state.next_input_byte);
+br_state.next_input_byte = buffer;
+BITREAD_SAVE_STATE(cinfo,entropy->bitstate);
+ASSIGN_STATE(entropy->saved, state);
+return TRUE;
+}
+/*
+* Decode and return one MCU's worth of Huffman-compressed coefficients.
+* The coefficients are reordered from zigzag order into natural array order,
+* but are not dequantized.
+*
+* The i'th block of the MCU is stored into the block pointed to by
+* MCU_data[i].  WE ASSUME THIS AREA HAS BEEN ZEROED BY THE CALLER.
+* (Wholesale zeroing is usually a little faster than retail...)
+*
+* Returns FALSE if data source requested suspension.  In that case no
+* changes have been made to permanent state.  (Exception: some output
+* coefficients may already have been assigned.  This is harmless for
+* this module, since we'll just re-assign them on the next call.)
+*/
+#define BUFSIZE (DCTSIZE2 * 2)
+METHODDEF(boolean)
+decode_mcu (j_decompress_ptr cinfo, JBLOCKROW *MCU_data)
+{
+huff_entropy_ptr entropy = (huff_entropy_ptr) cinfo->entropy;
+int usefast = 1;
+/* Process restart marker if needed; may have to suspend */
+if (cinfo->restart_interval) {
+if (entropy->restarts_to_go == 0)
+if (! process_restart(cinfo))
+	return FALSE;
+usefast = 0;
+}
+if (cinfo->src->bytes_in_buffer < BUFSIZE * (size_t)cinfo->blocks_in_MCU
+|| cinfo->unread_marker != 0)
+usefast = 0;
+/* If we've run out of data, just leave the MCU set to zeroes.
+* This way, we return uniform gray for the remainder of the segment.
+*/
+if (! entropy->pub.insufficient_data) {
+if (usefast) {
+if (!decode_mcu_fast(cinfo, MCU_data)) goto use_slow;
+}
+else {
+use_slow:
+if (!decode_mcu_slow(cinfo, MCU_data)) return FALSE;
+}
+}
+/* Account for restart interval (no-op if not using restarts) */
+entropy->restarts_to_go--;
+return TRUE;
+}
+/*
+* Module initialization routine for Huffman entropy decoding.
+*/
+GLOBAL(void)
+jinit_huff_decoder (j_decompress_ptr cinfo)
+{
+huff_entropy_ptr entropy;
+int i;
+/* Motion JPEG frames typically do not include the Huffman tables if they
+are the default tables.  Thus, if the tables are not set by the time
+the Huffman decoder is initialized (usually within the body of
+jpeg_start_decompress()), we set them to default values. */
+std_huff_tables((j_common_ptr) cinfo);
+entropy = (huff_entropy_ptr)
+(*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
+				SIZEOF(huff_entropy_decoder));
+cinfo->entropy = (struct jpeg_entropy_decoder *) entropy;
+entropy->pub.start_pass = start_pass_huff_decoder;
+entropy->pub.decode_mcu = decode_mcu;
+/* Mark tables unallocated */
+for (i = 0; i < NUM_HUFF_TBLS; i++) {
+entropy->dc_derived_tbls[i] = entropy->ac_derived_tbls[i] = NULL;
+}
+}

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media/libjpeg/jdhuff.c