/* * reserved comment block * DO NOT REMOVE OR ALTER!
*/ /* * jdphuff.c * * Copyright (C) 1995-1997, 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 for progressive JPEG. * * 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" #include"jdhuff.h"/* Declarations shared with jdhuff.c */
#ifdef D_PROGRESSIVE_SUPPORTED
/* * Expanded entropy decoder object for progressive Huffman decoding. * * The savable_state subrecord contains fields that change within an MCU, * but must not be updated permanently until we complete the MCU.
*/
typedefstruct { unsignedint 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.
*/
typedefstruct { 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. */ unsignedint restarts_to_go; /* MCUs left in this restart interval */
/* 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 */
} phuff_entropy_decoder;
/* Validate scan parameters */
bad = FALSE; if (is_DC_band) { if (cinfo->Se != 0)
bad = TRUE;
} else { /* need not check Ss/Se < 0 since they came from unsigned bytes */ if (cinfo->Ss > cinfo->Se || cinfo->Se >= DCTSIZE2)
bad = TRUE; /* AC scans may have only one component */ if (cinfo->comps_in_scan != 1)
bad = TRUE;
} if (cinfo->Ah != 0) { /* Successive approximation refinement scan: must have Al = Ah-1. */ if (cinfo->Al != cinfo->Ah-1)
bad = TRUE;
} if (cinfo->Al > 13) /* need not check for < 0 */
bad = TRUE; /* 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.
*/ if (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 cindex = cinfo->cur_comp_info[ci]->component_index;
coef_bit_ptr = & cinfo->coef_bits[cindex][0]; if (!is_DC_band && 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;
}
}
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 (is_DC_band) { if (cinfo->Ah == 0) { /* DC refinement needs no table */
tbl = compptr->dc_tbl_no;
jpeg_make_d_derived_tbl(cinfo, TRUE, tbl,
& entropy->derived_tbls[tbl]);
}
} else {
tbl = compptr->ac_tbl_no;
jpeg_make_d_derived_tbl(cinfo, FALSE, tbl,
& entropy->derived_tbls[tbl]); /* remember the single active table */
entropy->ac_derived_tbl = entropy->derived_tbls[tbl];
} /* Initialize DC predictions to 0 */
entropy->saved.last_dc_val[ci] = 0;
}
/* 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)) returnFALSE;
/* 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 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;
returnTRUE;
}
/* * 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. * * 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).
*/
/* Process restart marker if needed; may have to suspend */ if (cinfo->restart_interval) { if (entropy->restarts_to_go == 0) if (! process_restart(cinfo)) returnFALSE;
}
/* 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);
/* Decode a single block's worth of coefficients */
/* Section F.2.2.1: decode the DC coefficient difference */
HUFF_DECODE(s, br_state, tbl, returnFALSE, label1); if (s) {
CHECK_BIT_BUFFER(br_state, s, returnFALSE);
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--;
returnTRUE;
}
/* * 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)
{
phuff_entropy_ptr entropy = (phuff_entropy_ptr) cinfo->entropy; int Se = cinfo->Se; int Al = cinfo->Al; registerint s, k, r; unsignedint 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)) returnFALSE;
}
/* 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, returnFALSE, label2);
r = s >> 4;
s &= 15; if (s) {
k += r;
CHECK_BIT_BUFFER(br_state, s, returnFALSE);
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, returnFALSE);
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--;
returnTRUE;
}
/* * 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)
{
phuff_entropy_ptr entropy = (phuff_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)) returnFALSE;
}
/* 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);
/* Encoded data is simply the next bit of the two's-complement DC value */
CHECK_BIT_BUFFER(br_state, 1, returnFALSE); 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--;
returnTRUE;
}
/* * MCU decoding for AC successive approximation refinement scan.
*/
METHODDEF(boolean)
decode_mcu_AC_refine (j_decompress_ptr cinfo, JBLOCKROW *MCU_data)
{
phuff_entropy_ptr entropy = (phuff_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 */ registerint s, k, r; unsignedint 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)) returnFALSE;
}
/* 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--;
returnTRUE;
undoit: /* Re-zero any output coefficients that we made newly nonzero */ while (num_newnz > 0)
(*block)[newnz_pos[--num_newnz]] = 0;
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