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+/*
+ * jdhuff.c
+ *
+ * Copyright (C) 1991, Thomas G. Lane.
+ * 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.
+ * These routines are invoked via the methods entropy_decode
+ * and entropy_decoder_init/term.
+ */
+
+#include "jinclude.h"
+
+
+/* Static variables to avoid passing 'round extra parameters */
+
+static decompress_info_ptr dcinfo;
+
+static unsigned int get_buffer; /* current bit-extraction buffer */
+static int bits_left; /* # of unused bits in it */
+
+
+LOCAL void
+fix_huff_tbl (HUFF_TBL * htbl)
+/* Compute derived values for a Huffman table */
+{
+ int p, i, l, lastp, si;
+ char huffsize[257];
+ UINT16 huffcode[257];
+ UINT16 code;
+
+ /* Figure 7.3.5.4.2.1: make table of Huffman code length for each symbol */
+ /* Note that this is in code-length order. */
+
+ p = 0;
+ for (l = 1; l <= 16; l++) {
+ for (i = 1; i <= htbl->bits[l]; i++)
+ huffsize[p++] = l;
+ }
+ huffsize[p] = 0;
+ lastp = p;
+
+ /* Figure 7.3.5.4.2.2: generate the codes themselves */
+ /* Note that this is in code-length order. */
+
+ code = 0;
+ si = huffsize[0];
+ p = 0;
+ while (huffsize[p]) {
+ while (huffsize[p] == si) {
+ huffcode[p++] = code;
+ code++;
+ }
+ code <<= 1;
+ si++;
+ }
+
+ /* Figure 7.3.5.4.2.3: generate encoding tables */
+ /* These are code and size indexed by symbol value */
+
+ for (p = 0; p < lastp; p++) {
+ htbl->ehufco[htbl->huffval[p]] = huffcode[p];
+ htbl->ehufsi[htbl->huffval[p]] = huffsize[p];
+ }
+
+ /* Figure 13.4.2.3.1: generate decoding tables */
+
+ p = 0;
+ for (l = 1; l <= 16; l++) {
+ if (htbl->bits[l]) {
+ htbl->valptr[l] = p; /* huffval[] index of 1st sym of code len l */
+ htbl->mincode[l] = huffcode[p]; /* minimum code of length l */
+ p += htbl->bits[l];
+ htbl->maxcode[l] = huffcode[p-1]; /* maximum code of length l */
+ } else {
+ htbl->maxcode[l] = -1;
+ }
+ }
+}
+
+
+/* Extract the next N bits from the input stream (N <= 8) */
+
+LOCAL int
+get_bits (int nbits)
+{
+ int result;
+
+ while (nbits > bits_left) {
+ int c = JGETC(dcinfo);
+
+ get_buffer = (get_buffer << 8) + c;
+ bits_left += 8;
+ /* If it's 0xFF, check and discard stuffed zero byte */
+ if (c == 0xff) {
+ c = JGETC(dcinfo); /* Byte stuffing */
+ if (c != 0)
+ ERREXIT1(dcinfo->emethods,
+ "Unexpected marker 0x%02x in compressed data", c);
+ }
+ }
+
+ bits_left -= nbits;
+ result = (get_buffer >> bits_left) & ((1 << nbits) - 1);
+ return result;
+}
+
+/* Macro to make things go at some speed! */
+
+#define get_bit() (bits_left ? \
+ ((get_buffer >> (--bits_left)) & 1) : \
+ get_bits(1))
+
+
+/* Figure 13.4.2.3.2: extract next coded symbol from input stream */
+
+LOCAL int
+huff_DECODE (HUFF_TBL * htbl)
+{
+ int l, p;
+ INT32 code;
+
+ code = get_bit();
+ l = 1;
+ while (code > htbl->maxcode[l]) {
+ code = (code << 1) + get_bit();
+ l++;
+ }
+
+ p = htbl->valptr[l] + (code - htbl->mincode[l]);
+
+ return htbl->huffval[p];
+}
+
+
+/* Figure 13.4.2.1.1: extend sign bit */
+
+#define huff_EXTEND(x, s) ((x) < (1 << ((s)-1)) ? \
+ (x) + (-1 << (s)) + 1 : \
+ (x))
+
+
+/* Decode a single block's worth of coefficients */
+/* Note that only the difference is returned for the DC coefficient */
+
+LOCAL void
+decode_one_block (JBLOCK block, HUFF_TBL *dctbl, HUFF_TBL *actbl)
+{
+ int s, k, r, n;
+
+ /* zero out the coefficient block */
+
+ MEMZERO((void *) block, SIZEOF(JBLOCK));
+
+ /* Section 13.4.2.1: decode the DC coefficient difference */
+
+ s = huff_DECODE(dctbl);
+ r = get_bits(s);
+ block[0] = huff_EXTEND(r, s);
+
+ /* Section 13.4.2.2: decode the AC coefficients */
+
+ for (k = 1; k < DCTSIZE2; k++) {
+ r = huff_DECODE(actbl);
+
+ s = r & 15;
+ n = r >> 4;
+
+ if (s) {
+ k = k + n;
+ r = get_bits(s);
+ block[k] = huff_EXTEND(r, s);
+ } else {
+ if (n != 15)
+ break;
+ k += 15;
+ }
+ }
+}
+
+
+/*
+ * Initialize for a Huffman-compressed scan.
+ * This is invoked after reading the SOS marker.
+ */
+
+METHODDEF void
+huff_decoder_init (decompress_info_ptr cinfo)
+{
+ short ci;
+ jpeg_component_info * compptr;
+
+ /* Initialize static variables */
+ dcinfo = cinfo;
+ bits_left = 0;
+
+ for (ci = 0; ci < cinfo->comps_in_scan; ci++) {
+ compptr = cinfo->cur_comp_info[ci];
+ /* Make sure requested tables are present */
+ if (cinfo->dc_huff_tbl_ptrs[compptr->dc_tbl_no] == NULL ||
+ cinfo->ac_huff_tbl_ptrs[compptr->ac_tbl_no] == NULL)
+ ERREXIT(cinfo->emethods, "Use of undefined Huffman table");
+ /* Compute derived values for Huffman tables */
+ /* We may do this more than once for same table, but it's not a big deal */
+ fix_huff_tbl(cinfo->dc_huff_tbl_ptrs[compptr->dc_tbl_no]);
+ fix_huff_tbl(cinfo->ac_huff_tbl_ptrs[compptr->ac_tbl_no]);
+ /* Initialize DC predictions to 0 */
+ cinfo->last_dc_val[ci] = 0;
+ }
+
+ /* Initialize restart stuff */
+ cinfo->restarts_to_go = cinfo->restart_interval;
+ cinfo->next_restart_num = 0;
+}
+
+
+/*
+ * Check for a restart marker & resynchronize decoder.
+ */
+
+LOCAL void
+process_restart (decompress_info_ptr cinfo)
+{
+ int c, nbytes;
+ short ci;
+
+ /* Throw away any partial unread byte */
+ bits_left = 0;
+
+ /* Scan for next JPEG marker */
+ nbytes = 0;
+ do {
+ do { /* skip any non-FF bytes */
+ nbytes++;
+ c = JGETC(cinfo);
+ } while (c != 0xFF);
+ do { /* skip any duplicate FFs */
+ nbytes++;
+ c = JGETC(cinfo);
+ } while (c == 0xFF);
+ } while (c == 0); /* repeat if it was a stuffed FF/00 */
+
+ if (c != (RST0 + cinfo->next_restart_num))
+ ERREXIT2(cinfo->emethods, "Found 0x%02x marker instead of RST%d",
+ c, cinfo->next_restart_num);
+
+ if (nbytes != 2)
+ TRACEMS2(cinfo->emethods, 1, "Skipped %d bytes before RST%d",
+ nbytes-2, cinfo->next_restart_num);
+ else
+ TRACEMS1(cinfo->emethods, 2, "RST%d", cinfo->next_restart_num);
+
+ /* Re-initialize DC predictions to 0 */
+ for (ci = 0; ci < cinfo->comps_in_scan; ci++)
+ cinfo->last_dc_val[ci] = 0;
+
+ /* Update restart state */
+ cinfo->restarts_to_go = cinfo->restart_interval;
+ cinfo->next_restart_num++;
+ cinfo->next_restart_num &= 7;
+}
+
+
+/*
+ * Decode and return one MCU's worth of Huffman-compressed coefficients.
+ */
+
+METHODDEF void
+huff_decode (decompress_info_ptr cinfo, JBLOCK *MCU_data)
+{
+ short blkn, ci;
+ jpeg_component_info * compptr;
+
+ /* Account for restart interval, process restart marker if needed */
+ if (cinfo->restart_interval) {
+ if (cinfo->restarts_to_go == 0)
+ process_restart(cinfo);
+ cinfo->restarts_to_go--;
+ }
+
+ for (blkn = 0; blkn < cinfo->blocks_in_MCU; blkn++) {
+ ci = cinfo->MCU_membership[blkn];
+ compptr = cinfo->cur_comp_info[ci];
+ decode_one_block(MCU_data[blkn],
+ cinfo->dc_huff_tbl_ptrs[compptr->dc_tbl_no],
+ cinfo->ac_huff_tbl_ptrs[compptr->ac_tbl_no]);
+ /* Convert DC difference to actual value, update last_dc_val */
+ MCU_data[blkn][0] += cinfo->last_dc_val[ci];
+ cinfo->last_dc_val[ci] = MCU_data[blkn][0];
+ }
+}
+
+
+/*
+ * Finish up at the end of a Huffman-compressed scan.
+ */
+
+METHODDEF void
+huff_decoder_term (decompress_info_ptr cinfo)
+{
+ /* No work needed */
+}
+
+
+/*
+ * The method selection routine for Huffman entropy decoding.
+ */
+
+GLOBAL void
+jseldhuffman (decompress_info_ptr cinfo)
+{
+ if (! cinfo->arith_code) {
+ cinfo->methods->entropy_decoder_init = huff_decoder_init;
+ cinfo->methods->entropy_decode = huff_decode;
+ cinfo->methods->entropy_decoder_term = huff_decoder_term;
+ }
+}
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