/* * jdhuff.c * * Copyright (C) 1991-1997, Thomas G. Lane. * Modified 2006-2009 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 Huffman entropy decoding routines. * Both sequential and progressive modes are supported in this single module. * * 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" /* Derived data constructed for each Huffman table */ #define HUFF_LOOKAHEAD 8 /* # of bits of lookahead */ typedef struct { /* Basic tables: (element [0] of each array is unused) */ INT32 maxcode[18]; /* largest code of length k (-1 if none) */ /* (maxcode[17] is a sentinel to ensure jpeg_huff_decode terminates) */ INT32 valoffset[17]; /* huffval[] offset for codes of length k */ /* valoffset[k] = huffval[] index of 1st symbol of code length k, less * the smallest code of length k; so given a code of length k, the * corresponding symbol is huffval[code + valoffset[k]] */ /* Link to public Huffman table (needed only in jpeg_huff_decode) */ JHUFF_TBL *pub; /* Lookahead tables: indexed by the next HUFF_LOOKAHEAD bits of * the input data stream. If the next Huffman code is no more * than HUFF_LOOKAHEAD bits long, we can obtain its length and * the corresponding symbol directly from these tables. */ int look_nbits[1<<HUFF_LOOKAHEAD]; /* # bits, or 0 if too long */ UINT8 look_sym[1<<HUFF_LOOKAHEAD]; /* symbol, or unused */ } d_derived_tbl; /* * Fetching the next N bits from the input stream is a time-critical operation * for the Huffman decoders. We implement it with a combination of inline * macros and out-of-line subroutines. Note that N (the number of bits * demanded at one time) never exceeds 15 for JPEG use. * * We read source bytes into get_buffer and dole out bits as needed. * If get_buffer already contains enough bits, they are fetched in-line * by the macros CHECK_BIT_BUFFER and GET_BITS. When there aren't enough * bits, jpeg_fill_bit_buffer is called; it will attempt to fill get_buffer * as full as possible (not just to the number of bits needed; this * prefetching reduces the overhead cost of calling jpeg_fill_bit_buffer). * Note that jpeg_fill_bit_buffer may return FALSE to indicate suspension. * On TRUE return, jpeg_fill_bit_buffer guarantees that get_buffer contains * at least the requested number of bits --- dummy zeroes are inserted if * necessary. */ typedef INT32 bit_buf_type; /* type of bit-extraction buffer */ #define BIT_BUF_SIZE 32 /* size of buffer in bits */ /* If long is > 32 bits on your machine, and shifting/masking longs is * reasonably fast, making bit_buf_type be long and setting BIT_BUF_SIZE * appropriately should be a win. Unfortunately we can't define the size * with something like #define BIT_BUF_SIZE (sizeof(bit_buf_type)*8) * because not all machines measure sizeof in 8-bit bytes. */ typedef struct { /* Bitreading state saved across MCUs */ bit_buf_type get_buffer; /* current bit-extraction buffer */ int bits_left; /* # of unused bits in it */ } bitread_perm_state; typedef struct { /* Bitreading working state within an MCU */ /* Current data source location */ /* We need a copy, rather than munging the original, in case of suspension */ const JOCTET * next_input_byte; /* => next byte to read from source */ size_t bytes_in_buffer; /* # of bytes remaining in source buffer */ /* Bit input buffer --- note these values are kept in register variables, * not in this struct, inside the inner loops. */ bit_buf_type get_buffer; /* current bit-extraction buffer */ int bits_left; /* # of unused bits in it */ /* Pointer needed by jpeg_fill_bit_buffer. */ j_decompress_ptr cinfo; /* back link to decompress master record */ } bitread_working_state; /* Macros to declare and load/save bitread local variables. */ #define BITREAD_STATE_VARS \ register bit_buf_type get_buffer; \ register int bits_left; \ bitread_working_state br_state #define BITREAD_LOAD_STATE(cinfop,permstate) \ br_state.cinfo = cinfop; \ br_state.next_input_byte = cinfop->src->next_input_byte; \ br_state.bytes_in_buffer = cinfop->src->bytes_in_buffer; \ get_buffer = permstate.get_buffer; \ bits_left = permstate.bits_left; #define BITREAD_SAVE_STATE(cinfop,permstate) \ cinfop->src->next_input_byte = br_state.next_input_byte; \ cinfop->src->bytes_in_buffer = br_state.bytes_in_buffer; \ permstate.get_buffer = get_buffer; \ permstate.bits_left = bits_left /* * These macros provide the in-line portion of bit fetching. * Use CHECK_BIT_BUFFER to ensure there are N bits in get_buffer * before using GET_BITS, PEEK_BITS, or DROP_BITS. * The variables get_buffer and bits_left are assumed to be locals, * but the state struct might not be (jpeg_huff_decode needs this). * CHECK_BIT_BUFFER(state,n,action); * Ensure there are N bits in get_buffer; if suspend, take action. * val = GET_BITS(n); * Fetch next N bits. * val = PEEK_BITS(n); * Fetch next N bits without removing them from the buffer. * DROP_BITS(n); * Discard next N bits. * The value N should be a simple variable, not an expression, because it * is evaluated multiple times. */ #define CHECK_BIT_BUFFER(state,nbits,action) \ { if (bits_left < (nbits)) { \ if (! jpeg_fill_bit_buffer(&(state),get_buffer,bits_left,nbits)) \ { action; } \ get_buffer = (state).get_buffer; bits_left = (state).bits_left; } } #define GET_BITS(nbits) \ (((int) (get_buffer >> (bits_left -= (nbits)))) & BIT_MASK(nbits)) #define PEEK_BITS(nbits) \ (((int) (get_buffer >> (bits_left - (nbits)))) & BIT_MASK(nbits)) #define DROP_BITS(nbits) \ (bits_left -= (nbits)) /* * Code for extracting next Huffman-coded symbol from input bit stream. * Again, this is time-critical and we make the main paths be macros. * * We use a lookahead table to process codes of up to HUFF_LOOKAHEAD bits * without looping. Usually, more than 95% of the Huffman codes will be 8 * or fewer bits long. The few overlength codes are handled with a loop, * which need not be inline code. * * Notes about the HUFF_DECODE macro: * 1. Near the end of the data segment, we may fail to get enough bits * for a lookahead. In that case, we do it the hard way. * 2. If the lookahead table contains no entry, the next code must be * more than HUFF_LOOKAHEAD bits long. * 3. jpeg_huff_decode returns -1 if forced to suspend. */ #define HUFF_DECODE(result,state,htbl,failaction,slowlabel) \ { register int nb, look; \ if (bits_left < HUFF_LOOKAHEAD) { \ if (! jpeg_fill_bit_buffer(&state,get_buffer,bits_left, 0)) {failaction;} \ get_buffer = state.get_buffer; bits_left = state.bits_left; \ if (bits_left < HUFF_LOOKAHEAD) { \ nb = 1; goto slowlabel; \ } \ } \ look = PEEK_BITS(HUFF_LOOKAHEAD); \ if ((nb = htbl->look_nbits[look]) != 0) { \ DROP_BITS(nb); \ result = htbl->look_sym[look]; \ } else { \ nb = HUFF_LOOKAHEAD+1; \ slowlabel: \ if ((result=jpeg_huff_decode(&state,get_buffer,bits_left,htbl,nb)) < 0) \ { failaction; } \ get_buffer = state.get_buffer; bits_left = state.bits_left; \ } \ } /* * 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 { unsigned int EOBRUN; /* remaining EOBs in EOBRUN */ 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).EOBRUN = (src).EOBRUN, \ (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 */ /* Following two fields used only in progressive mode */ /* Pointers to derived tables (these workspaces have image lifespan) */ d_derived_tbl * derived_tbls[NUM_HUFF_TBLS]; d_derived_tbl * ac_derived_tbl; /* active table during an AC scan */ /* Following fields used only in sequential mode */ /* 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 */ int coef_limit[D_MAX_BLOCKS_IN_MCU]; } huff_entropy_decoder; typedef huff_entropy_decoder * huff_entropy_ptr; static const int jpeg_zigzag_order[8][8] = { { 0, 1, 5, 6, 14, 15, 27, 28 }, { 2, 4, 7, 13, 16, 26, 29, 42 }, { 3, 8, 12, 17, 25, 30, 41, 43 }, { 9, 11, 18, 24, 31, 40, 44, 53 }, { 10, 19, 23, 32, 39, 45, 52, 54 }, { 20, 22, 33, 38, 46, 51, 55, 60 }, { 21, 34, 37, 47, 50, 56, 59, 61 }, { 35, 36, 48, 49, 57, 58, 62, 63 } }; /* * Compute the derived values for a Huffman table. * This routine also performs some validation checks on the table. */ LOCAL(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->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. */ MEMZERO(dtbl->look_nbits, SIZEOF(dtbl->look_nbits)); 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->look_nbits[lookbits] = l; dtbl->look_sym[lookbits] = 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. * 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 LOCAL(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; } /* * Figure F.12: extend sign bit. * On some machines, a shift and sub will be faster than a table lookup. */ #ifdef AVOID_TABLES #define BIT_MASK(nbits) ((1<<(nbits))-1) #define HUFF_EXTEND(x,s) ((x) < (1<<((s)-1)) ? (x) - ((1<<(s))-1) : (x)) #else #define BIT_MASK(nbits) bmask[nbits] #define HUFF_EXTEND(x,s) ((x) <= bmask[(s) - 1] ? (x) - bmask[s] : (x)) static const int bmask[16] = /* bmask[n] is mask for n rightmost bits */ { 0, 0x0001, 0x0003, 0x0007, 0x000F, 0x001F, 0x003F, 0x007F, 0x00FF, 0x01FF, 0x03FF, 0x07FF, 0x0FFF, 0x1FFF, 0x3FFF, 0x7FFF }; #endif /* AVOID_TABLES */ /* * Out-of-line code for Huffman code decoding. */ LOCAL(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]) ]; } /* * 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; /* Re-init EOB run count, too */ entropy->saved.EOBRUN = 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; } /* * Huffman MCU decoding. * Each of these routines decodes and returns 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 IS INITIALLY ZEROED BY THE CALLER. * (Wholesale zeroing is usually a little faster than retail...) * * We return 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 * spectral selection, since we'll just re-assign them on the next call. * Successive approximation AC refinement has to be more careful, however.) */ /* * MCU decoding for DC initial scan (either spectral selection, * or first pass of successive approximation). */ METHODDEF(boolean) decode_mcu_DC_first (j_decompress_ptr cinfo, JBLOCKROW *MCU_data) { huff_entropy_ptr entropy = (huff_entropy_ptr) cinfo->entropy; int Al = cinfo->Al; register int s, r; int blkn, ci; JBLOCKROW block; BITREAD_STATE_VARS; savable_state state; d_derived_tbl * tbl; jpeg_component_info * compptr; /* 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; } /* 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) { /* Load up working state */ BITREAD_LOAD_STATE(cinfo,entropy->bitstate); ASSIGN_STATE(state, entropy->saved); /* Outer loop handles each block in the MCU */ for (blkn = 0; blkn < cinfo->blocks_in_MCU; blkn++) { block = MCU_data[blkn]; ci = cinfo->MCU_membership[blkn]; compptr = cinfo->cur_comp_info[ci]; tbl = entropy->derived_tbls[compptr->dc_tbl_no]; /* Decode a single block's worth of coefficients */ /* Section F.2.2.1: decode the DC coefficient difference */ HUFF_DECODE(s, br_state, tbl, return FALSE, label1); if (s) { CHECK_BIT_BUFFER(br_state, s, return FALSE); r = GET_BITS(s); s = HUFF_EXTEND(r, s); } /* Convert DC difference to actual value, update last_dc_val */ s += state.last_dc_val[ci]; state.last_dc_val[ci] = s; /* Scale and output the coefficient (assumes jpeg_natural_order[0]=0) */ (*block)[0] = (JCOEF) (s << Al); } /* Completed MCU, so update state */ BITREAD_SAVE_STATE(cinfo,entropy->bitstate); ASSIGN_STATE(entropy->saved, state); } /* Account for restart interval (no-op if not using restarts) */ entropy->restarts_to_go--; return TRUE; } /* * MCU decoding for AC initial scan (either spectral selection, * or first pass of successive approximation). */ METHODDEF(boolean) decode_mcu_AC_first (j_decompress_ptr cinfo, JBLOCKROW *MCU_data) { huff_entropy_ptr entropy = (huff_entropy_ptr) cinfo->entropy; int Se = cinfo->Se; int Al = cinfo->Al; register int s, k, r; unsigned int EOBRUN; JBLOCKROW block; BITREAD_STATE_VARS; d_derived_tbl * tbl; /* 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; } /* 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) { /* Load up working state. * We can avoid loading/saving bitread state if in an EOB run. */ EOBRUN = entropy->saved.EOBRUN; /* only part of saved state we need */ /* There is always only one block per MCU */ if (EOBRUN > 0) /* if it's a band of zeroes... */ EOBRUN--; /* ...process it now (we do nothing) */ else { BITREAD_LOAD_STATE(cinfo,entropy->bitstate); block = MCU_data[0]; tbl = entropy->ac_derived_tbl; for (k = cinfo->Ss; k <= Se; k++) { HUFF_DECODE(s, br_state, tbl, 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); /* Scale and output coefficient in natural (dezigzagged) order */ (*block)[jpeg_natural_order[k]] = (JCOEF) (s << Al); } else { if (r == 15) { /* ZRL */ k += 15; /* skip 15 zeroes in band */ } else { /* EOBr, run length is 2^r + appended bits */ EOBRUN = 1 << r; if (r) { /* EOBr, r > 0 */ CHECK_BIT_BUFFER(br_state, r, return FALSE); r = GET_BITS(r); EOBRUN += r; } EOBRUN--; /* this band is processed at this moment */ break; /* force end-of-band */ } } } BITREAD_SAVE_STATE(cinfo,entropy->bitstate); } /* Completed MCU, so update state */ entropy->saved.EOBRUN = EOBRUN; /* only part of saved state we need */ } /* Account for restart interval (no-op if not using restarts) */ entropy->restarts_to_go--; return TRUE; } /* * MCU decoding for DC successive approximation refinement scan. * Note: we assume such scans can be multi-component, although the spec * is not very clear on the point. */ METHODDEF(boolean) decode_mcu_DC_refine (j_decompress_ptr cinfo, JBLOCKROW *MCU_data) { huff_entropy_ptr entropy = (huff_entropy_ptr) cinfo->entropy; int p1 = 1 << cinfo->Al; /* 1 in the bit position being coded */ int blkn; JBLOCKROW block; BITREAD_STATE_VARS; /* 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; } /* Not worth the cycles to check insufficient_data here, * since we will not change the data anyway if we read zeroes. */ /* Load up working state */ BITREAD_LOAD_STATE(cinfo,entropy->bitstate); /* Outer loop handles each block in the MCU */ for (blkn = 0; blkn < cinfo->blocks_in_MCU; blkn++) { block = MCU_data[blkn]; /* Encoded data is simply the next bit of the two's-complement DC value */ CHECK_BIT_BUFFER(br_state, 1, return FALSE); if (GET_BITS(1)) (*block)[0] |= p1; /* Note: since we use |=, repeating the assignment later is safe */ } /* Completed MCU, so update state */ BITREAD_SAVE_STATE(cinfo,entropy->bitstate); /* Account for restart interval (no-op if not using restarts) */ entropy->restarts_to_go--; return TRUE; } /* * MCU decoding for AC successive approximation refinement scan. */ METHODDEF(boolean) decode_mcu_AC_refine (j_decompress_ptr cinfo, JBLOCKROW *MCU_data) { huff_entropy_ptr entropy = (huff_entropy_ptr) cinfo->entropy; int Se = cinfo->Se; int p1 = 1 << cinfo->Al; /* 1 in the bit position being coded */ int m1 = (-1) << cinfo->Al; /* -1 in the bit position being coded */ register int s, k, r; unsigned int EOBRUN; JBLOCKROW block; JCOEFPTR thiscoef; BITREAD_STATE_VARS; d_derived_tbl * tbl; int num_newnz; int newnz_pos[DCTSIZE2]; /* 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; } /* If we've run out of data, don't modify the MCU. */ if (! entropy->pub.insufficient_data) { /* Load up working state */ BITREAD_LOAD_STATE(cinfo,entropy->bitstate); EOBRUN = entropy->saved.EOBRUN; /* only part of saved state we need */ /* There is always only one block per MCU */ block = MCU_data[0]; tbl = entropy->ac_derived_tbl; /* If we are forced to suspend, we must undo the assignments to any newly * nonzero coefficients in the block, because otherwise we'd get confused * next time about which coefficients were already nonzero. * But we need not undo addition of bits to already-nonzero coefficients; * instead, we can test the current bit to see if we already did it. */ num_newnz = 0; /* initialize coefficient loop counter to start of band */ k = cinfo->Ss; if (EOBRUN == 0) { for (; k <= Se; k++) { HUFF_DECODE(s, br_state, tbl, goto undoit, label3); r = s >> 4; s &= 15; if (s) { if (s != 1) /* size of new coef should always be 1 */ WARNMS(cinfo, JWRN_HUFF_BAD_CODE); CHECK_BIT_BUFFER(br_state, 1, goto undoit); if (GET_BITS(1)) s = p1; /* newly nonzero coef is positive */ else s = m1; /* newly nonzero coef is negative */ } else { if (r != 15) { EOBRUN = 1 << r; /* EOBr, run length is 2^r + appended bits */ if (r) { CHECK_BIT_BUFFER(br_state, r, goto undoit); r = GET_BITS(r); EOBRUN += r; } break; /* rest of block is handled by EOB logic */ } /* note s = 0 for processing ZRL */ } /* Advance over already-nonzero coefs and r still-zero coefs, * appending correction bits to the nonzeroes. A correction bit is 1 * if the absolute value of the coefficient must be increased. */ do { thiscoef = *block + jpeg_natural_order[k]; if (*thiscoef != 0) { CHECK_BIT_BUFFER(br_state, 1, goto undoit); if (GET_BITS(1)) { if ((*thiscoef & p1) == 0) { /* do nothing if already set it */ if (*thiscoef >= 0) *thiscoef += p1; else *thiscoef += m1; } } } else { if (--r < 0) break; /* reached target zero coefficient */ } k++; } while (k <= Se); if (s) { int pos = jpeg_natural_order[k]; /* Output newly nonzero coefficient */ (*block)[pos] = (JCOEF) s; /* Remember its position in case we have to suspend */ newnz_pos[num_newnz++] = pos; } } } if (EOBRUN > 0) { /* Scan any remaining coefficient positions after the end-of-band * (the last newly nonzero coefficient, if any). Append a correction * bit to each already-nonzero coefficient. A correction bit is 1 * if the absolute value of the coefficient must be increased. */ for (; k <= Se; k++) { thiscoef = *block + jpeg_natural_order[k]; if (*thiscoef != 0) { CHECK_BIT_BUFFER(br_state, 1, goto undoit); if (GET_BITS(1)) { if ((*thiscoef & p1) == 0) { /* do nothing if already changed it */ if (*thiscoef >= 0) *thiscoef += p1; else *thiscoef += m1; } } } } /* Count one block completed in EOB run */ EOBRUN--; } /* Completed MCU, so update state */ BITREAD_SAVE_STATE(cinfo,entropy->bitstate); entropy->saved.EOBRUN = EOBRUN; /* only part of saved state we need */ } /* Account for restart interval (no-op if not using restarts) */ entropy->restarts_to_go--; return TRUE; undoit: /* Re-zero any output coefficients that we made newly nonzero */ while (num_newnz > 0) (*block)[newnz_pos[--num_newnz]] = 0; return FALSE; } /* * Decode one MCU's worth of Huffman-compressed coefficients. */ METHODDEF(boolean) decode_mcu (j_decompress_ptr cinfo, JBLOCKROW *MCU_data) { huff_entropy_ptr entropy = (huff_entropy_ptr) cinfo->entropy; int blkn; BITREAD_STATE_VARS; savable_state state; /* 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; } /* 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) { /* Load up working state */ BITREAD_LOAD_STATE(cinfo,entropy->bitstate); ASSIGN_STATE(state, entropy->saved); /* Outer loop handles each block in the MCU */ for (blkn = 0; blkn < cinfo->blocks_in_MCU; blkn++) { JBLOCKROW block = MCU_data[blkn]; d_derived_tbl * htbl; register int s, k, r; int coef_limit, ci; /* Decode a single block's worth of coefficients */ /* Section F.2.2.1: decode the DC coefficient difference */ htbl = entropy->dc_cur_tbls[blkn]; HUFF_DECODE(s, br_state, htbl, return FALSE, label1); htbl = entropy->ac_cur_tbls[blkn]; k = 1; coef_limit = entropy->coef_limit[blkn]; if (coef_limit) { /* Convert DC difference to actual value, update last_dc_val */ if (s) { CHECK_BIT_BUFFER(br_state, s, return FALSE); r = GET_BITS(s); s = HUFF_EXTEND(r, s); } ci = cinfo->MCU_membership[blkn]; s += state.last_dc_val[ci]; state.last_dc_val[ci] = s; /* Output the DC coefficient */ (*block)[0] = (JCOEF) s; /* Section F.2.2.2: decode the AC coefficients */ /* Since zeroes are skipped, output area must be cleared beforehand */ for (; k < coef_limit; k++) { HUFF_DECODE(s, br_state, htbl, 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) goto EndOfBlock; k += 15; } } } else { if (s) { CHECK_BIT_BUFFER(br_state, s, return FALSE); DROP_BITS(s); } } /* Section F.2.2.2: decode the AC coefficients */ /* In this path we just discard the values */ for (; k < DCTSIZE2; k++) { HUFF_DECODE(s, br_state, htbl, 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; } } EndOfBlock: ; } /* Completed MCU, so update state */ BITREAD_SAVE_STATE(cinfo,entropy->bitstate); ASSIGN_STATE(entropy->saved, state); } /* Account for restart interval (no-op if not using restarts) */ entropy->restarts_to_go--; return TRUE; } /* * 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, i; jpeg_component_info * compptr; if (cinfo->progressive_mode) { /* Validate progressive scan parameters */ if (cinfo->Ss == 0) { if (cinfo->Se != 0) goto bad; } else { /* need not check Ss/Se < 0 since they came from unsigned bytes */ if (cinfo->Se < cinfo->Ss || cinfo->Se >= DCTSIZE2) goto bad; /* AC scans may have only one component */ if (cinfo->comps_in_scan != 1) goto bad; } if (cinfo->Ah != 0) { /* Successive approximation refinement scan: must have Al = Ah-1. */ if (cinfo->Ah-1 != cinfo->Al) goto bad; } if (cinfo->Al > 13) { /* need not check for < 0 */ /* Arguably the maximum Al value should be less than 13 for 8-bit precision, * but the spec doesn't say so, and we try to be liberal about what we * accept. Note: large Al values could result in out-of-range DC * coefficients during early scans, leading to bizarre displays due to * overflows in the IDCT math. But we won't crash. */ bad: ERREXIT4(cinfo, JERR_BAD_PROGRESSION, cinfo->Ss, cinfo->Se, cinfo->Ah, cinfo->Al); } /* Update progression status, and verify that scan order is legal. * Note that inter-scan inconsistencies are treated as warnings * not fatal errors ... not clear if this is right way to behave. */ for (ci = 0; ci < cinfo->comps_in_scan; ci++) { int coefi, cindex = cinfo->cur_comp_info[ci]->component_index; int *coef_bit_ptr = & cinfo->coef_bits[cindex][0]; if (cinfo->Ss && coef_bit_ptr[0] < 0) /* AC without prior DC scan */ WARNMS2(cinfo, JWRN_BOGUS_PROGRESSION, cindex, 0); for (coefi = cinfo->Ss; coefi <= cinfo->Se; coefi++) { int expected = (coef_bit_ptr[coefi] < 0) ? 0 : coef_bit_ptr[coefi]; if (cinfo->Ah != expected) WARNMS2(cinfo, JWRN_BOGUS_PROGRESSION, cindex, coefi); coef_bit_ptr[coefi] = cinfo->Al; } } /* Select MCU decoding routine */ if (cinfo->Ah == 0) { if (cinfo->Ss == 0) entropy->pub.decode_mcu = decode_mcu_DC_first; else entropy->pub.decode_mcu = decode_mcu_AC_first; } else { if (cinfo->Ss == 0) entropy->pub.decode_mcu = decode_mcu_DC_refine; else entropy->pub.decode_mcu = decode_mcu_AC_refine; } for (ci = 0; ci < cinfo->comps_in_scan; ci++) { compptr = cinfo->cur_comp_info[ci]; /* Make sure requested tables are present, and compute derived tables. * We may build same derived table more than once, but it's not expensive. */ if (cinfo->Ss == 0) { if (cinfo->Ah == 0) { /* DC refinement needs no table */ i = compptr->dc_tbl_no; jpeg_make_d_derived_tbl(cinfo, TRUE, i, & entropy->derived_tbls[i]); } } else { i = compptr->ac_tbl_no; jpeg_make_d_derived_tbl(cinfo, FALSE, i, & entropy->derived_tbls[i]); /* remember the single active table */ entropy->ac_derived_tbl = entropy->derived_tbls[i]; } /* Initialize DC predictions to 0 */ entropy->saved.last_dc_val[ci] = 0; } /* Initialize private state variables */ entropy->saved.EOBRUN = 0; } else { /* 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); /* Select MCU decoding routine */ entropy->pub.decode_mcu = decode_mcu; 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) { ci = compptr->DCT_v_scaled_size; if (ci <= 0 || ci > 8) ci = 8; i = compptr->DCT_h_scaled_size; if (i <= 0 || i > 8) i = 8; entropy->coef_limit[blkn] = 1 + jpeg_zigzag_order[ci - 1][i - 1]; } else { entropy->coef_limit[blkn] = 0; } } } /* 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; } /* * Module initialization routine for Huffman entropy decoding. */ GLOBAL(void) jinit_huff_decoder (j_decompress_ptr cinfo) { huff_entropy_ptr entropy; int i; 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; if (cinfo->progressive_mode) { /* Create progression status table */ int *coef_bit_ptr, ci; cinfo->coef_bits = (int (*)[DCTSIZE2]) (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE, cinfo->num_components*DCTSIZE2*SIZEOF(int)); coef_bit_ptr = & cinfo->coef_bits[0][0]; for (ci = 0; ci < cinfo->num_components; ci++) for (i = 0; i < DCTSIZE2; i++) *coef_bit_ptr++ = -1; /* Mark derived tables unallocated */ for (i = 0; i < NUM_HUFF_TBLS; i++) { entropy->derived_tbls[i] = NULL; } } else { /* 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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