417 lines
12 KiB
C
417 lines
12 KiB
C
/*
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* jdhuff.c
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*
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* Copyright (C) 1991, 1992, Thomas G. Lane.
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* This file is part of the Independent JPEG Group's software.
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* For conditions of distribution and use, see the accompanying README file.
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*
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* This file contains Huffman entropy decoding routines.
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* These routines are invoked via the methods entropy_decode
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* and entropy_decode_init/term.
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*/
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#include "jinclude.h"
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/* Static variables to avoid passing 'round extra parameters */
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static decompress_info_ptr dcinfo;
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static INT32 get_buffer; /* current bit-extraction buffer */
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static int bits_left; /* # of unused bits in it */
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static boolean printed_eod; /* flag to suppress multiple end-of-data msgs */
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LOCAL void
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fix_huff_tbl (HUFF_TBL * htbl)
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/* Compute derived values for a Huffman table */
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{
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int p, i, l, si;
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char huffsize[257];
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UINT16 huffcode[257];
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UINT16 code;
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/* Figure C.1: make table of Huffman code length for each symbol */
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/* Note that this is in code-length order. */
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p = 0;
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for (l = 1; l <= 16; l++) {
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for (i = 1; i <= (int) htbl->bits[l]; i++)
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huffsize[p++] = (char) l;
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}
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huffsize[p] = 0;
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/* Figure C.2: generate the codes themselves */
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/* Note that this is in code-length order. */
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code = 0;
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si = huffsize[0];
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p = 0;
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while (huffsize[p]) {
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while (((int) huffsize[p]) == si) {
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huffcode[p++] = code;
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code++;
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}
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code <<= 1;
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si++;
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}
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/* We don't bother to fill in the encoding tables ehufco[] and ehufsi[], */
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/* since they are not used for decoding. */
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/* Figure F.15: generate decoding tables */
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p = 0;
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for (l = 1; l <= 16; l++) {
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if (htbl->bits[l]) {
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htbl->valptr[l] = p; /* huffval[] index of 1st sym of code len l */
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htbl->mincode[l] = huffcode[p]; /* minimum code of length l */
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p += htbl->bits[l];
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htbl->maxcode[l] = huffcode[p-1]; /* maximum code of length l */
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} else {
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htbl->maxcode[l] = -1;
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}
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}
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htbl->maxcode[17] = 0xFFFFFL; /* ensures huff_DECODE terminates */
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}
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/*
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* Code for extracting the next N bits from the input stream.
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* (N never exceeds 15 for JPEG data.)
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* This needs to go as fast as possible!
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*
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* We read source bytes into get_buffer and dole out bits as needed.
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* If get_buffer already contains enough bits, they are fetched in-line
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* by the macros get_bits() and get_bit(). When there aren't enough bits,
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* fill_bit_buffer is called; it will attempt to fill get_buffer to the
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* "high water mark", then extract the desired number of bits. The idea,
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* of course, is to minimize the function-call overhead cost of entering
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* fill_bit_buffer.
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* On most machines MIN_GET_BITS should be 25 to allow the full 32-bit width
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* of get_buffer to be used. (On machines with wider words, an even larger
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* buffer could be used.) However, on some machines 32-bit shifts are
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* relatively slow and take time proportional to the number of places shifted.
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* (This is true with most PC compilers, for instance.) In this case it may
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* be a win to set MIN_GET_BITS to the minimum value of 15. This reduces the
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* average shift distance at the cost of more calls to fill_bit_buffer.
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*/
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#ifdef SLOW_SHIFT_32
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#define MIN_GET_BITS 15 /* minimum allowable value */
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#else
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#define MIN_GET_BITS 25 /* max value for 32-bit get_buffer */
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#endif
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static const int bmask[16] = /* bmask[n] is mask for n rightmost bits */
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{ 0, 0x0001, 0x0003, 0x0007, 0x000F, 0x001F, 0x003F, 0x007F, 0x00FF,
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0x01FF, 0x03FF, 0x07FF, 0x0FFF, 0x1FFF, 0x3FFF, 0x7FFF };
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LOCAL int
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fill_bit_buffer (int nbits)
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/* Load up the bit buffer and do get_bits(nbits) */
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{
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/* Attempt to load at least MIN_GET_BITS bits into get_buffer. */
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while (bits_left < MIN_GET_BITS) {
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register int c = JGETC(dcinfo);
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/* If it's 0xFF, check and discard stuffed zero byte */
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if (c == 0xFF) {
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int c2 = JGETC(dcinfo);
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if (c2 != 0) {
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/* Oops, it's actually a marker indicating end of compressed data. */
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/* Better put it back for use later */
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JUNGETC(c2,dcinfo);
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JUNGETC(c,dcinfo);
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/* There should be enough bits still left in the data segment; */
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/* if so, just break out of the while loop. */
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if (bits_left >= nbits)
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break;
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/* Uh-oh. Report corrupted data to user and stuff zeroes into
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* the data stream, so we can produce some kind of image.
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* Note that this will be repeated for each byte demanded for the
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* rest of the segment; this is a bit slow but not unreasonably so.
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* The main thing is to avoid getting a zillion warnings, hence:
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*/
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if (! printed_eod) {
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WARNMS(dcinfo->emethods, "Corrupt JPEG data: premature end of data segment");
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printed_eod = TRUE;
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}
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c = 0; /* insert a zero byte into bit buffer */
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}
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}
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/* OK, load c into get_buffer */
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get_buffer = (get_buffer << 8) | c;
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bits_left += 8;
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}
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/* Having filled get_buffer, extract desired bits (this simplifies macros) */
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bits_left -= nbits;
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return ((int) (get_buffer >> bits_left)) & bmask[nbits];
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}
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/* Macros to make things go at some speed! */
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/* NB: parameter to get_bits should be simple variable, not expression */
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#define get_bits(nbits) \
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(bits_left >= (nbits) ? \
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((int) (get_buffer >> (bits_left -= (nbits)))) & bmask[nbits] : \
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fill_bit_buffer(nbits))
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#define get_bit() \
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(bits_left ? \
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((int) (get_buffer >> (--bits_left))) & 1 : \
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fill_bit_buffer(1))
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/* Figure F.16: extract next coded symbol from input stream */
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INLINE
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LOCAL int
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huff_DECODE (HUFF_TBL * htbl)
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{
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register int l;
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register INT32 code;
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code = get_bit();
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l = 1;
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while (code > htbl->maxcode[l]) {
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code = (code << 1) | get_bit();
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l++;
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}
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/* With garbage input we may reach the sentinel value l = 17. */
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if (l > 16) {
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WARNMS(dcinfo->emethods, "Corrupt JPEG data: bad Huffman code");
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return 0; /* fake a zero as the safest result */
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}
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return htbl->huffval[ htbl->valptr[l] + ((int) (code - htbl->mincode[l])) ];
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}
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/* Figure F.12: extend sign bit */
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#define huff_EXTEND(x,s) ((x) < extend_test[s] ? (x) + extend_offset[s] : (x))
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static const int extend_test[16] = /* entry n is 2**(n-1) */
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{ 0, 0x0001, 0x0002, 0x0004, 0x0008, 0x0010, 0x0020, 0x0040, 0x0080,
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0x0100, 0x0200, 0x0400, 0x0800, 0x1000, 0x2000, 0x4000 };
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static const int extend_offset[16] = /* entry n is (-1 << n) + 1 */
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{ 0, ((-1)<<1) + 1, ((-1)<<2) + 1, ((-1)<<3) + 1, ((-1)<<4) + 1,
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((-1)<<5) + 1, ((-1)<<6) + 1, ((-1)<<7) + 1, ((-1)<<8) + 1,
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((-1)<<9) + 1, ((-1)<<10) + 1, ((-1)<<11) + 1, ((-1)<<12) + 1,
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((-1)<<13) + 1, ((-1)<<14) + 1, ((-1)<<15) + 1 };
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/*
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* Initialize for a Huffman-compressed scan.
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* This is invoked after reading the SOS marker.
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*/
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METHODDEF void
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huff_decoder_init (decompress_info_ptr cinfo)
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{
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short ci;
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jpeg_component_info * compptr;
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/* Initialize static variables */
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dcinfo = cinfo;
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bits_left = 0;
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printed_eod = FALSE;
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for (ci = 0; ci < cinfo->comps_in_scan; ci++) {
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compptr = cinfo->cur_comp_info[ci];
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/* Make sure requested tables are present */
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if (cinfo->dc_huff_tbl_ptrs[compptr->dc_tbl_no] == NULL ||
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cinfo->ac_huff_tbl_ptrs[compptr->ac_tbl_no] == NULL)
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ERREXIT(cinfo->emethods, "Use of undefined Huffman table");
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/* Compute derived values for Huffman tables */
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/* We may do this more than once for same table, but it's not a big deal */
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fix_huff_tbl(cinfo->dc_huff_tbl_ptrs[compptr->dc_tbl_no]);
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fix_huff_tbl(cinfo->ac_huff_tbl_ptrs[compptr->ac_tbl_no]);
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/* Initialize DC predictions to 0 */
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cinfo->last_dc_val[ci] = 0;
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}
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/* Initialize restart stuff */
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cinfo->restarts_to_go = cinfo->restart_interval;
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cinfo->next_restart_num = 0;
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}
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/*
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* Check for a restart marker & resynchronize decoder.
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*/
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LOCAL void
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process_restart (decompress_info_ptr cinfo)
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{
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int c, nbytes;
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short ci;
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/* Throw away any unused bits remaining in bit buffer */
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nbytes = bits_left / 8; /* count any full bytes loaded into buffer */
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bits_left = 0;
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printed_eod = FALSE; /* next segment can get another warning */
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/* Scan for next JPEG marker */
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do {
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do { /* skip any non-FF bytes */
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nbytes++;
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c = JGETC(cinfo);
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} while (c != 0xFF);
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do { /* skip any duplicate FFs */
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/* we don't increment nbytes here since extra FFs are legal */
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c = JGETC(cinfo);
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} while (c == 0xFF);
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} while (c == 0); /* repeat if it was a stuffed FF/00 */
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if (nbytes != 1)
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WARNMS2(cinfo->emethods,
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"Corrupt JPEG data: %d extraneous bytes before marker 0x%02x",
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nbytes-1, c);
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if (c != (RST0 + cinfo->next_restart_num)) {
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/* Uh-oh, the restart markers have been messed up too. */
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/* Let the file-format module try to figure out how to resync. */
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(*cinfo->methods->resync_to_restart) (cinfo, c);
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} else
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TRACEMS1(cinfo->emethods, 2, "RST%d", cinfo->next_restart_num);
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/* Re-initialize DC predictions to 0 */
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for (ci = 0; ci < cinfo->comps_in_scan; ci++)
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cinfo->last_dc_val[ci] = 0;
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/* Update restart state */
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cinfo->restarts_to_go = cinfo->restart_interval;
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cinfo->next_restart_num = (cinfo->next_restart_num + 1) & 7;
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}
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/* ZAG[i] is the natural-order position of the i'th element of zigzag order.
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* If the incoming data is corrupted, huff_decode_mcu could attempt to
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* reference values beyond the end of the array. To avoid a wild store,
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* we put some extra zeroes after the real entries.
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*/
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static const short ZAG[DCTSIZE2+16] = {
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0, 1, 8, 16, 9, 2, 3, 10,
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17, 24, 32, 25, 18, 11, 4, 5,
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12, 19, 26, 33, 40, 48, 41, 34,
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27, 20, 13, 6, 7, 14, 21, 28,
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35, 42, 49, 56, 57, 50, 43, 36,
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29, 22, 15, 23, 30, 37, 44, 51,
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58, 59, 52, 45, 38, 31, 39, 46,
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53, 60, 61, 54, 47, 55, 62, 63,
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0, 0, 0, 0, 0, 0, 0, 0, /* extra entries in case k>63 below */
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0, 0, 0, 0, 0, 0, 0, 0
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};
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/*
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* Decode and return one MCU's worth of Huffman-compressed coefficients.
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* This routine also handles quantization descaling and zigzag reordering
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* of coefficient values.
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*
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* The i'th block of the MCU is stored into the block pointed to by
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* MCU_data[i]. WE ASSUME THIS AREA HAS BEEN ZEROED BY THE CALLER.
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* (Wholesale zeroing is usually a little faster than retail...)
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*/
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METHODDEF void
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huff_decode_mcu (decompress_info_ptr cinfo, JBLOCKROW *MCU_data)
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{
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register int s, k, r;
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short blkn, ci;
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register JBLOCKROW block;
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register QUANT_TBL_PTR quanttbl;
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HUFF_TBL *dctbl;
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HUFF_TBL *actbl;
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jpeg_component_info * compptr;
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/* Account for restart interval, process restart marker if needed */
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if (cinfo->restart_interval) {
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if (cinfo->restarts_to_go == 0)
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process_restart(cinfo);
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cinfo->restarts_to_go--;
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}
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/* Outer loop handles each block in the MCU */
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for (blkn = 0; blkn < cinfo->blocks_in_MCU; blkn++) {
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block = MCU_data[blkn];
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ci = cinfo->MCU_membership[blkn];
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compptr = cinfo->cur_comp_info[ci];
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quanttbl = cinfo->quant_tbl_ptrs[compptr->quant_tbl_no];
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actbl = cinfo->ac_huff_tbl_ptrs[compptr->ac_tbl_no];
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dctbl = cinfo->dc_huff_tbl_ptrs[compptr->dc_tbl_no];
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/* Decode a single block's worth of coefficients */
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/* Section F.2.2.1: decode the DC coefficient difference */
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s = huff_DECODE(dctbl);
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if (s) {
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r = get_bits(s);
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s = huff_EXTEND(r, s);
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}
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/* Convert DC difference to actual value, update last_dc_val */
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s += cinfo->last_dc_val[ci];
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cinfo->last_dc_val[ci] = (JCOEF) s;
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/* Descale and output the DC coefficient (assumes ZAG[0] = 0) */
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(*block)[0] = (JCOEF) (((JCOEF) s) * quanttbl[0]);
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/* Section F.2.2.2: decode the AC coefficients */
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/* Since zero values are skipped, output area must be zeroed beforehand */
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for (k = 1; k < DCTSIZE2; k++) {
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r = huff_DECODE(actbl);
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s = r & 15;
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r = r >> 4;
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if (s) {
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k += r;
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r = get_bits(s);
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s = huff_EXTEND(r, s);
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/* Descale coefficient and output in natural (dezigzagged) order */
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(*block)[ZAG[k]] = (JCOEF) (((JCOEF) s) * quanttbl[k]);
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} else {
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if (r != 15)
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break;
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k += 15;
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}
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}
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}
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}
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/*
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* Finish up at the end of a Huffman-compressed scan.
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*/
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METHODDEF void
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huff_decoder_term (decompress_info_ptr cinfo)
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{
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/* No work needed */
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}
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/*
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* The method selection routine for Huffman entropy decoding.
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*/
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GLOBAL void
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jseldhuffman (decompress_info_ptr cinfo)
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{
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if (! cinfo->arith_code) {
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cinfo->methods->entropy_decode_init = huff_decoder_init;
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cinfo->methods->entropy_decode = huff_decode_mcu;
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cinfo->methods->entropy_decode_term = huff_decoder_term;
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}
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}
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