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