-
-
-/*
- * Figure F.12: extend sign bit.
- * On some machines, a shift and add will be faster than a table lookup.
- */
-
-#ifdef AVOID_TABLES
-
-#define HUFF_EXTEND(x,s) ((x) < (1<<((s)-1)) ? (x) + (((-1)<<(s)) + 1) : (x))
-
-#else
-
-#define HUFF_EXTEND(x,s) ((x) < extend_test[s] ? (x) + extend_offset[s] : (x))
-
-static const int extend_test[16] = /* entry n is 2**(n-1) */
- { 0, 0x0001, 0x0002, 0x0004, 0x0008, 0x0010, 0x0020, 0x0040, 0x0080,
- 0x0100, 0x0200, 0x0400, 0x0800, 0x1000, 0x2000, 0x4000 };
-
-static const int extend_offset[16] = /* entry n is (-1 << n) + 1 */
- { 0, ((-1)<<1) + 1, ((-1)<<2) + 1, ((-1)<<3) + 1, ((-1)<<4) + 1,
- ((-1)<<5) + 1, ((-1)<<6) + 1, ((-1)<<7) + 1, ((-1)<<8) + 1,
- ((-1)<<9) + 1, ((-1)<<10) + 1, ((-1)<<11) + 1, ((-1)<<12) + 1,
- ((-1)<<13) + 1, ((-1)<<14) + 1, ((-1)<<15) + 1 };
-
-#endif /* AVOID_TABLES */
-
-
-/*
- * Check for a restart marker & resynchronize decoder.
- * Returns FALSE if must suspend.
- */
-
-LOCAL(boolean)
-process_restart (j_decompress_ptr cinfo)
-{
- huff_entropy_ptr entropy = (huff_entropy_ptr) cinfo->entropy;
- int ci;
-
- /* Throw away any unused bits remaining in bit buffer; */
- /* include any full bytes in next_marker's count of discarded bytes */
- cinfo->marker->discarded_bytes += entropy->bitstate.bits_left / 8;
- entropy->bitstate.bits_left = 0;
-
- /* Advance past the RSTn marker */
- if (! (*cinfo->marker->read_restart_marker) (cinfo))
- return FALSE;
-
- /* Re-initialize DC predictions to 0 */
- for (ci = 0; ci < cinfo->comps_in_scan; ci++)
- entropy->saved.last_dc_val[ci] = 0;
-
- /* Reset restart counter */
- entropy->restarts_to_go = cinfo->restart_interval;
-
- /* Reset out-of-data flag, unless read_restart_marker left us smack up
- * against a marker. In that case we will end up treating the next data
- * segment as empty, and we can avoid producing bogus output pixels by
- * leaving the flag set.
- */
- if (cinfo->unread_marker == 0)
- entropy->pub.insufficient_data = FALSE;
-
- return TRUE;
-}
-
-
-/*
- * Decode and return one MCU's worth of Huffman-compressed coefficients.
- * The coefficients are reordered from zigzag order into natural array order,
- * but are not dequantized.
- *
- * The i'th block of the MCU is stored into the block pointed to by
- * MCU_data[i]. WE ASSUME THIS AREA HAS BEEN ZEROED BY THE CALLER.
- * (Wholesale zeroing is usually a little faster than retail...)
- *
- * Returns FALSE if data source requested suspension. In that case no
- * changes have been made to permanent state. (Exception: some output
- * coefficients may already have been assigned. This is harmless for
- * this module, since we'll just re-assign them on the next call.)
- */
-
-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 * dctbl = entropy->dc_cur_tbls[blkn];
- d_derived_tbl * actbl = entropy->ac_cur_tbls[blkn];
- register int s, k, r;
-
- /* Decode a single block's worth of coefficients */
-
- /* Section F.2.2.1: decode the DC coefficient difference */
- HUFF_DECODE(s, br_state, dctbl, return FALSE, label1);
- if (s) {
- CHECK_BIT_BUFFER(br_state, s, return FALSE);
- r = GET_BITS(s);
- s = HUFF_EXTEND(r, s);
- }
-
- if (entropy->dc_needed[blkn]) {
- /* Convert DC difference to actual value, update last_dc_val */
- int ci = cinfo->MCU_membership[blkn];
- s += state.last_dc_val[ci];
- state.last_dc_val[ci] = s;
- /* Output the DC coefficient (assumes jpeg_natural_order[0] = 0) */
- (*block)[0] = (JCOEF) s;
- }
-
- if (entropy->ac_needed[blkn]) {
-
- /* Section F.2.2.2: decode the AC coefficients */
- /* Since zeroes are skipped, output area must be cleared beforehand */
- for (k = 1; k < DCTSIZE2; k++) {
- HUFF_DECODE(s, br_state, actbl, return FALSE, label2);
-
- r = s >> 4;
- s &= 15;
-
- if (s) {
- k += r;
- CHECK_BIT_BUFFER(br_state, s, return FALSE);
- r = GET_BITS(s);
- s = HUFF_EXTEND(r, s);
- /* Output coefficient in natural (dezigzagged) order.
- * Note: the extra entries in jpeg_natural_order[] will save us
- * if k >= DCTSIZE2, which could happen if the data is corrupted.
- */
- (*block)[jpeg_natural_order[k]] = (JCOEF) s;
- } else {
- if (r != 15)
- break;
- k += 15;
- }
- }
-
- } else {
-
- /* Section F.2.2.2: decode the AC coefficients */
- /* In this path we just discard the values */
- for (k = 1; k < DCTSIZE2; k++) {
- HUFF_DECODE(s, br_state, actbl, return FALSE, label3);
-
- r = s >> 4;
- s &= 15;
-
- if (s) {
- k += r;
- CHECK_BIT_BUFFER(br_state, s, return FALSE);
- DROP_BITS(s);
- } else {
- if (r != 15)
- break;
- k += 15;
- }
- }
-
- }
- }
-
- /* Completed MCU, so update state */
- BITREAD_SAVE_STATE(cinfo,entropy->bitstate);
- ASSIGN_STATE(entropy->saved, state);
- }
-
- /* Account for restart interval (no-op if not using restarts) */
- entropy->restarts_to_go--;
-
- return TRUE;
-}
-
-
-/*
- * Module initialization routine for Huffman entropy decoding.
- */
-
-GLOBAL(void)
-jinit_huff_decoder (j_decompress_ptr cinfo)
-{
- huff_entropy_ptr entropy;
- int i;
-
- entropy = (huff_entropy_ptr)
- (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
- SIZEOF(huff_entropy_decoder));
- cinfo->entropy = (struct jpeg_entropy_decoder *) entropy;
- entropy->pub.start_pass = start_pass_huff_decoder;
- entropy->pub.decode_mcu = decode_mcu;
-
- /* Mark tables unallocated */
- for (i = 0; i < NUM_HUFF_TBLS; i++) {
- entropy->dc_derived_tbls[i] = entropy->ac_derived_tbls[i] = NULL;
- }
-}