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CentrED/Imaging/JpegLib/imjdhuff.pas

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unit imjdhuff;
{ This file contains declarations for Huffman entropy decoding routines
that are shared between the sequential decoder (jdhuff.c) and the
progressive decoder (jdphuff.c). No other modules need to see these. }
{ This file contains Huffman entropy decoding routines.
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. }
{ Original: jdhuff.h+jdhuff.c; Copyright (C) 1991-1997, Thomas G. Lane. }
interface
{$I imjconfig.inc}
uses
imjmorecfg,
imjinclude,
imjdeferr,
imjerror,
imjutils,
imjpeglib;
{ Declarations shared with jdphuff.c }
{ Derived data constructed for each Huffman table }
const
HUFF_LOOKAHEAD = 8; { # of bits of lookahead }
type
d_derived_tbl_ptr = ^d_derived_tbl;
d_derived_tbl = record
{ Basic tables: (element [0] of each array is unused) }
maxcode : array[0..18-1] of INT32; { largest code of length k (-1 if none) }
{ (maxcode[17] is a sentinel to ensure jpeg_huff_decode terminates) }
valoffset : array[0..17-1] of INT32; { 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) }
pub : JHUFF_TBL_PTR;
{ 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. }
look_nbits : array[0..(1 shl HUFF_LOOKAHEAD)-1] of int;
{ # bits, or 0 if too long }
look_sym : array[0..(1 shl HUFF_LOOKAHEAD)-1] of UINT8;
{ symbol, or unused }
end;
{ 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. }
type
bit_buf_type = INT32 ; { type of bit-extraction buffer }
const
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. }
type
bitread_perm_state = record { Bitreading state saved across MCUs }
get_buffer : bit_buf_type; { current bit-extraction buffer }
bits_left : int; { # of unused bits in it }
end;
type
bitread_working_state = record
{ Bitreading working state within an MCU }
{ current data source location }
{ We need a copy, rather than munging the original, in case of suspension }
next_input_byte : JOCTETptr; { => next byte to read from source }
bytes_in_buffer : size_t; { # 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. }
get_buffer : bit_buf_type; { current bit-extraction buffer }
bits_left : int; { # of unused bits in it }
{ Pointer needed by jpeg_fill_bit_buffer }
cinfo : j_decompress_ptr; { back link to decompress master record }
end;
{ Module initialization routine for Huffman entropy decoding. }
{GLOBAL}
procedure jinit_huff_decoder (cinfo : j_decompress_ptr);
{GLOBAL}
function jpeg_huff_decode(var state : bitread_working_state;
get_buffer : bit_buf_type; {register}
bits_left : int; {register}
htbl : d_derived_tbl_ptr;
min_bits : int) : int;
{ Compute the derived values for a Huffman table.
Note this is also used by jdphuff.c. }
{GLOBAL}
procedure jpeg_make_d_derived_tbl (cinfo : j_decompress_ptr;
isDC : boolean;
tblno : int;
var pdtbl : d_derived_tbl_ptr);
{ Load up the bit buffer to a depth of at least nbits }
function jpeg_fill_bit_buffer (var state : bitread_working_state;
get_buffer : bit_buf_type; {register}
bits_left : int; {register}
nbits : int) : boolean;
implementation
{$IFDEF MACRO}
{ Macros to declare and load/save bitread local variables. }
{$define BITREAD_STATE_VARS}
get_buffer : bit_buf_type ; {register}
bits_left : int; {register}
br_state : bitread_working_state;
{$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)) then
begin
if (not jpeg_fill_bit_buffer(&(state),get_buffer,bits_left,nbits)) then
begin
action;
exit;
end;
get_buffer := state.get_buffer;
bits_left := state.bits_left;
end;
{$define GET_BITS(nbits)}
Dec(bits_left, (nbits));
( (int(get_buffer shr bits_left)) and ( pred(1 shl (nbits)) ) )
{$define PEEK_BITS(nbits)}
int(get_buffer shr (bits_left - (nbits))) and pred(1 shl (nbits))
{$define DROP_BITS(nbits)}
Dec(bits_left, nbits);
{ Code for extracting next Huffman-coded symbol from input bit stream.
Again, this is time-critical and we make the main paths be macros.
We use a lookahead table to process codes of up to HUFF_LOOKAHEAD bits
without looping. Usually, more than 95% of the Huffman codes will be 8
or fewer bits long. The few overlength codes are handled with a loop,
which need not be inline code.
Notes about the HUFF_DECODE macro:
1. Near the end of the data segment, we may fail to get enough bits
for a lookahead. In that case, we do it the hard way.
2. If the lookahead table contains no entry, the next code must be
more than HUFF_LOOKAHEAD bits long.
3. jpeg_huff_decode returns -1 if forced to suspend. }
macro HUFF_DECODE(s,br_state,htbl,return FALSE,slowlabel);
label showlabel;
var
nb, look : int; {register}
begin
if (bits_left < HUFF_LOOKAHEAD) then
begin
if (not jpeg_fill_bit_buffer(br_state,get_buffer,bits_left, 0)) then
begin
decode_mcu := FALSE;
exit;
end;
get_buffer := br_state.get_buffer;
bits_left := br_state.bits_left;
if (bits_left < HUFF_LOOKAHEAD) then
begin
nb := 1;
goto slowlabel;
end;
end;
{look := PEEK_BITS(HUFF_LOOKAHEAD);}
look := int(get_buffer shr (bits_left - HUFF_LOOKAHEAD)) and
pred(1 shl HUFF_LOOKAHEAD);
nb := htbl^.look_nbits[look];
if (nb <> 0) then
begin
{DROP_BITS(nb);}
Dec(bits_left, nb);
s := htbl^.look_sym[look];
end
else
begin
nb := HUFF_LOOKAHEAD+1;
slowlabel:
s := jpeg_huff_decode(br_state,get_buffer,bits_left,htbl,nb));
if (s < 0) then
begin
result := FALSE;
exit;
end;
get_buffer := br_state.get_buffer;
bits_left := br_state.bits_left;
end;
end;
{$ENDIF} {MACRO}
{ 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. }
type
savable_state = record
last_dc_val : array[0..MAX_COMPS_IN_SCAN-1] of int; { last DC coef for each component }
end;
type
huff_entropy_ptr = ^huff_entropy_decoder;
huff_entropy_decoder = record
pub : jpeg_entropy_decoder; { public fields }
{ These fields are loaded into local variables at start of each MCU.
In case of suspension, we exit WITHOUT updating them. }
bitstate : bitread_perm_state; { Bit buffer at start of MCU }
saved : savable_state; { Other state at start of MCU }
{ These fields are NOT loaded into local working state. }
restarts_to_go : uInt; { MCUs left in this restart interval }
{ Pointers to derived tables (these workspaces have image lifespan) }
dc_derived_tbls : array[0..NUM_HUFF_TBLS] of d_derived_tbl_ptr;
ac_derived_tbls : array[0..NUM_HUFF_TBLS] of d_derived_tbl_ptr;
{ 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 }
dc_cur_tbls : array[0..D_MAX_BLOCKS_IN_MCU-1] of d_derived_tbl_ptr;
ac_cur_tbls : array[0..D_MAX_BLOCKS_IN_MCU-1] of d_derived_tbl_ptr;
{ Whether we care about the DC and AC coefficient values for each block }
dc_needed : array[0..D_MAX_BLOCKS_IN_MCU-1] of boolean;
ac_needed : array[0..D_MAX_BLOCKS_IN_MCU-1] of boolean;
end;
{ Initialize for a Huffman-compressed scan. }
{METHODDEF}
procedure start_pass_huff_decoder (cinfo : j_decompress_ptr);
var
entropy : huff_entropy_ptr;
ci, blkn, dctbl, actbl : int;
compptr : jpeg_component_info_ptr;
begin
entropy := huff_entropy_ptr (cinfo^.entropy);
{ 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) or (cinfo^.Se <> DCTSIZE2-1) or
(cinfo^.Ah <> 0) or (cinfo^.Al <> 0) then
WARNMS(j_common_ptr(cinfo), JWRN_NOT_SEQUENTIAL);
for ci := 0 to pred(cinfo^.comps_in_scan) do
begin
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;
end;
{ Precalculate decoding info for each block in an MCU of this scan }
for blkn := 0 to pred(cinfo^.blocks_in_MCU) do
begin
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) then
begin
entropy^.dc_needed[blkn] := TRUE;
{ we don't need the ACs if producing a 1/8th-size image }
entropy^.ac_needed[blkn] := (compptr^.DCT_scaled_size > 1);
end
else
begin
entropy^.ac_needed[blkn] := FALSE;
entropy^.dc_needed[blkn] := FALSE;
end;
end;
{ 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;
end;
{ Compute the derived values for a Huffman table.
This routine also performs some validation checks on the table.
Note this is also used by jdphuff.c. }
{GLOBAL}
procedure jpeg_make_d_derived_tbl (cinfo : j_decompress_ptr;
isDC : boolean;
tblno : int;
var pdtbl : d_derived_tbl_ptr);
var
htbl : JHUFF_TBL_PTR;
dtbl : d_derived_tbl_ptr;
p, i, l, si, numsymbols : int;
lookbits, ctr : int;
huffsize : array[0..257-1] of byte;
huffcode : array[0..257-1] of uInt;
code : uInt;
var
sym : int;
begin
{ 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) or (tblno >= NUM_HUFF_TBLS) then
ERREXIT1(j_common_ptr(cinfo), JERR_NO_HUFF_TABLE, tblno);
if isDC then
htbl := cinfo^.dc_huff_tbl_ptrs[tblno]
else
htbl := cinfo^.ac_huff_tbl_ptrs[tblno];
if (htbl = NIL) then
ERREXIT1(j_common_ptr(cinfo), JERR_NO_HUFF_TABLE, tblno);
{ Allocate a workspace if we haven't already done so. }
if (pdtbl = NIL) then
pdtbl := d_derived_tbl_ptr(
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 to 16 do
begin
i := int(htbl^.bits[l]);
if (i < 0) or (p + i > 256) then { protect against table overrun }
ERREXIT(j_common_ptr(cinfo), JERR_BAD_HUFF_TABLE);
while (i > 0) do
begin
huffsize[p] := byte(l);
Inc(p);
Dec(i);
end;
end;
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] <> 0) do
begin
while (( int (huffsize[p]) ) = si) do
begin
huffcode[p] := code;
Inc(p);
Inc(code);
end;
{ 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) shl si)) then
ERREXIT(j_common_ptr(cinfo), JERR_BAD_HUFF_TABLE);
code := code shl 1;
Inc(si);
end;
{ Figure F.15: generate decoding tables for bit-sequential decoding }
p := 0;
for l := 1 to 16 do
begin
if (htbl^.bits[l] <> 0) then
begin
{ 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]);
Inc(p, htbl^.bits[l]);
dtbl^.maxcode[l] := huffcode[p-1]; { maximum code of length l }
end
else
begin
dtbl^.maxcode[l] := -1; { -1 if no codes of this length }
end;
end;
dtbl^.maxcode[17] := long($FFFFF); { 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 to HUFF_LOOKAHEAD do
begin
for i := 1 to int (htbl^.bits[l]) do
begin
{ l := current code's length, p := its index in huffcode[] & huffval[]. }
{ Generate left-justified code followed by all possible bit sequences }
lookbits := huffcode[p] shl (HUFF_LOOKAHEAD-l);
for ctr := pred(1 shl (HUFF_LOOKAHEAD-l)) downto 0 do
begin
dtbl^.look_nbits[lookbits] := l;
dtbl^.look_sym[lookbits] := htbl^.huffval[p];
Inc(lookbits);
end;
Inc(p);
end;
end;
{ 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) then
begin
for i := 0 to pred(numsymbols) do
begin
sym := htbl^.huffval[i];
if (sym < 0) or (sym > 15) then
ERREXIT(j_common_ptr(cinfo), JERR_BAD_HUFF_TABLE);
end;
end;
end;
{ Out-of-line code for bit fetching (shared with jdphuff.c).
See jdhuff.h for info about usage.
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}
const
MIN_GET_BITS = 15; { minimum allowable value }
{$else}
const
MIN_GET_BITS = (BIT_BUF_SIZE-7);
{$endif}
{GLOBAL}
function jpeg_fill_bit_buffer (var state : bitread_working_state;
{register} get_buffer : bit_buf_type;
{register} bits_left : int;
nbits : int) : boolean;
label
no_more_bytes;
{ Load up the bit buffer to a depth of at least nbits }
var
{ Copy heavily used state fields into locals (hopefully registers) }
{register} next_input_byte : {const} JOCTETptr;
{register} bytes_in_buffer : size_t;
var
{register} c : int;
var
cinfo : j_decompress_ptr;
begin
next_input_byte := state.next_input_byte;
bytes_in_buffer := state.bytes_in_buffer;
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) then { cannot advance past a marker }
begin
while (bits_left < MIN_GET_BITS) do
begin
{ Attempt to read a byte }
if (bytes_in_buffer = 0) then
begin
if not cinfo^.src^.fill_input_buffer(cinfo) then
begin
jpeg_fill_bit_buffer := FALSE;
exit;
end;
next_input_byte := cinfo^.src^.next_input_byte;
bytes_in_buffer := cinfo^.src^.bytes_in_buffer;
end;
Dec(bytes_in_buffer);
c := GETJOCTET(next_input_byte^);
Inc(next_input_byte);
{ If it's $FF, check and discard stuffed zero byte }
if (c = $FF) then
begin
{ 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. }
repeat
if (bytes_in_buffer = 0) then
begin
if (not state.cinfo^.src^.fill_input_buffer (state.cinfo)) then
begin
jpeg_fill_bit_buffer := FALSE;
exit;
end;
next_input_byte := state.cinfo^.src^.next_input_byte;
bytes_in_buffer := state.cinfo^.src^.bytes_in_buffer;
end;
Dec(bytes_in_buffer);
c := GETJOCTET(next_input_byte^);
Inc(next_input_byte);
Until (c <> $FF);
if (c = 0) then
begin
{ Found FF/00, which represents an FF data byte }
c := $FF;
end
else
begin
{ 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;
end;
end;
{ OK, load c into get_buffer }
get_buffer := (get_buffer shl 8) or c;
Inc(bits_left, 8);
end { end while }
end
else
begin
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) then
begin
{ 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 not cinfo^.entropy^.insufficient_data then
begin
WARNMS(j_common_ptr(cinfo), JWRN_HIT_MARKER);
cinfo^.entropy^.insufficient_data := TRUE;
end;
{ Fill the buffer with zero bits }
get_buffer := get_buffer shl (MIN_GET_BITS - bits_left);
bits_left := MIN_GET_BITS;
end;
end;
{ 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;
jpeg_fill_bit_buffer := TRUE;
end;
{ Out-of-line code for Huffman code decoding.
See jdhuff.h for info about usage. }
{GLOBAL}
function jpeg_huff_decode (var state : bitread_working_state;
{register} get_buffer : bit_buf_type;
{register} bits_left : int;
htbl : d_derived_tbl_ptr;
min_bits : int) : int;
var
{register} l : int;
{register} code : INT32;
begin
l := min_bits;
{ 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);}
if (bits_left < l) then
begin
if (not jpeg_fill_bit_buffer(state, get_buffer, bits_left, l)) then
begin
jpeg_huff_decode := -1;
exit;
end;
get_buffer := state.get_buffer;
bits_left := state.bits_left;
end;
{code := GET_BITS(l);}
Dec(bits_left, l);
code := (int(get_buffer shr bits_left)) and ( pred(1 shl 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]) do
begin
code := code shl 1;
{CHECK_BIT_BUFFER(state, 1, return -1);}
if (bits_left < 1) then
begin
if (not jpeg_fill_bit_buffer(state, get_buffer, bits_left, 1)) then
begin
jpeg_huff_decode := -1;
exit;
end;
get_buffer := state.get_buffer;
bits_left := state.bits_left;
end;
{code := code or GET_BITS(1);}
Dec(bits_left);
code := code or ( (int(get_buffer shr bits_left)) and pred(1 shl 1) );
Inc(l);
end;
{ 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) then
begin
WARNMS(j_common_ptr(state.cinfo), JWRN_HUFF_BAD_CODE);
jpeg_huff_decode := 0; { fake a zero as the safest result }
exit;
end;
jpeg_huff_decode := htbl^.pub^.huffval[ int (code + htbl^.valoffset[l]) ];
end;
{ 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)
if (x < extend_test[s]) then
:= x + extend_offset[s]
else
x;}
const
extend_test : array[0..16-1] of int = { entry n is 2**(n-1) }
($0000, $0001, $0002, $0004, $0008, $0010, $0020, $0040,
$0080, $0100, $0200, $0400, $0800, $1000, $2000, $4000);
const
extend_offset : array[0..16-1] of int = { entry n is (-1 << n) + 1 }
(0, ((-1) shl 1) + 1, ((-1) shl 2) + 1, ((-1) shl 3) + 1, ((-1) shl 4) + 1,
((-1) shl 5) + 1, ((-1) shl 6) + 1, ((-1) shl 7) + 1, ((-1) shl 8) + 1,
((-1) shl 9) + 1, ((-1) shl 10) + 1, ((-1) shl 11) + 1,((-1) shl 12) + 1,
((-1) shl 13) + 1, ((-1) shl 14) + 1, ((-1) shl 15) + 1);
{$endif} { AVOID_TABLES }
{ Check for a restart marker & resynchronize decoder.
Returns FALSE if must suspend. }
{LOCAL}
function process_restart (cinfo : j_decompress_ptr) : boolean;
var
entropy : huff_entropy_ptr;
ci : int;
begin
entropy := huff_entropy_ptr (cinfo^.entropy);
{ Throw away any unused bits remaining in bit buffer; }
{ include any full bytes in next_marker's count of discarded bytes }
Inc(cinfo^.marker^.discarded_bytes, entropy^.bitstate.bits_left div 8);
entropy^.bitstate.bits_left := 0;
{ Advance past the RSTn marker }
if (not cinfo^.marker^.read_restart_marker (cinfo)) then
begin
process_restart := FALSE;
exit;
end;
{ Re-initialize DC predictions to 0 }
for ci := 0 to pred(cinfo^.comps_in_scan) do
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) then
entropy^.pub.insufficient_data := FALSE;
process_restart := TRUE;
end;
{ 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}
function decode_mcu (cinfo : j_decompress_ptr;
var MCU_data : array of JBLOCKROW) : boolean;
label
label1, label2, label3;
var
entropy : huff_entropy_ptr;
{register} s, k, r : int;
blkn, ci : int;
block : JBLOCK_PTR;
{BITREAD_STATE_VARS}
get_buffer : bit_buf_type ; {register}
bits_left : int; {register}
br_state : bitread_working_state;
state : savable_state;
dctbl : d_derived_tbl_ptr;
actbl : d_derived_tbl_ptr;
var
nb, look : int; {register}
begin
entropy := huff_entropy_ptr (cinfo^.entropy);
{ Process restart marker if needed; may have to suspend }
if (cinfo^.restart_interval <> 0) then
begin
if (entropy^.restarts_to_go = 0) then
if (not process_restart(cinfo)) then
begin
decode_mcu := FALSE;
exit;
end;
end;
{ 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 not entropy^.pub.insufficient_data then
begin
{ Load up working state }
{BITREAD_LOAD_STATE(cinfo,entropy^.bitstate);}
br_state.cinfo := cinfo;
br_state.next_input_byte := cinfo^.src^.next_input_byte;
br_state.bytes_in_buffer := cinfo^.src^.bytes_in_buffer;
get_buffer := entropy^.bitstate.get_buffer;
bits_left := entropy^.bitstate.bits_left;
{ASSIGN_STATE(state, entropy^.saved);}
state := entropy^.saved;
{ Outer loop handles each block in the MCU }
for blkn := 0 to pred(cinfo^.blocks_in_MCU) do
begin
block := JBLOCK_PTR(MCU_data[blkn]);
dctbl := entropy^.dc_cur_tbls[blkn];
actbl := entropy^.ac_cur_tbls[blkn];
{ 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 (bits_left < HUFF_LOOKAHEAD) then
begin
if (not jpeg_fill_bit_buffer(br_state,get_buffer,bits_left, 0)) then
begin
decode_mcu := False;
exit;
end;
get_buffer := br_state.get_buffer;
bits_left := br_state.bits_left;
if (bits_left < HUFF_LOOKAHEAD) then
begin
nb := 1;
goto label1;
end;
end;
{look := PEEK_BITS(HUFF_LOOKAHEAD);}
look := int(get_buffer shr (bits_left - HUFF_LOOKAHEAD)) and
pred(1 shl HUFF_LOOKAHEAD);
nb := dctbl^.look_nbits[look];
if (nb <> 0) then
begin
{DROP_BITS(nb);}
Dec(bits_left, nb);
s := dctbl^.look_sym[look];
end
else
begin
nb := HUFF_LOOKAHEAD+1;
label1:
s := jpeg_huff_decode(br_state,get_buffer,bits_left,dctbl,nb);
if (s < 0) then
begin
decode_mcu := FALSE;
exit;
end;
get_buffer := br_state.get_buffer;
bits_left := br_state.bits_left;
end;
if (s <> 0) then
begin
{CHECK_BIT_BUFFER(br_state, s, return FALSE);}
if (bits_left < s) then
begin
if (not jpeg_fill_bit_buffer(br_state,get_buffer,bits_left,s)) then
begin
decode_mcu := FALSE;
exit;
end;
get_buffer := br_state.get_buffer;
bits_left := br_state.bits_left;
end;
{r := GET_BITS(s);}
Dec(bits_left, s);
r := ( int(get_buffer shr bits_left)) and ( pred(1 shl s) );
{s := HUFF_EXTEND(r, s);}
if (r < extend_test[s]) then
s := r + extend_offset[s]
else
s := r;
end;
if (entropy^.dc_needed[blkn]) then
begin
{ Convert DC difference to actual value, update last_dc_val }
ci := cinfo^.MCU_membership[blkn];
Inc(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);
end;
if (entropy^.ac_needed[blkn]) then
begin
{ Section F.2.2.2: decode the AC coefficients }
{ Since zeroes are skipped, output area must be cleared beforehand }
k := 1;
while (k < DCTSIZE2) do { Nomssi: k is incr. in the loop }
begin
{HUFF_DECODE(s, br_state, actbl, return FALSE, label2);}
if (bits_left < HUFF_LOOKAHEAD) then
begin
if (not jpeg_fill_bit_buffer(br_state,get_buffer,bits_left, 0)) then
begin
decode_mcu := False;
exit;
end;
get_buffer := br_state.get_buffer;
bits_left := br_state.bits_left;
if (bits_left < HUFF_LOOKAHEAD) then
begin
nb := 1;
goto label2;
end;
end;
{look := PEEK_BITS(HUFF_LOOKAHEAD);}
look := int(get_buffer shr (bits_left - HUFF_LOOKAHEAD)) and
pred(1 shl HUFF_LOOKAHEAD);
nb := actbl^.look_nbits[look];
if (nb <> 0) then
begin
{DROP_BITS(nb);}
Dec(bits_left, nb);
s := actbl^.look_sym[look];
end
else
begin
nb := HUFF_LOOKAHEAD+1;
label2:
s := jpeg_huff_decode(br_state,get_buffer,bits_left,actbl,nb);
if (s < 0) then
begin
decode_mcu := FALSE;
exit;
end;
get_buffer := br_state.get_buffer;
bits_left := br_state.bits_left;
end;
r := s shr 4;
s := s and 15;
if (s <> 0) then
begin
Inc(k, r);
{CHECK_BIT_BUFFER(br_state, s, return FALSE);}
if (bits_left < s) then
begin
if (not jpeg_fill_bit_buffer(br_state,get_buffer,bits_left,s)) then
begin
decode_mcu := FALSE;
exit;
end;
get_buffer := br_state.get_buffer;
bits_left := br_state.bits_left;
end;
{r := GET_BITS(s);}
Dec(bits_left, s);
r := (int(get_buffer shr bits_left)) and ( pred(1 shl s) );
{s := HUFF_EXTEND(r, s);}
if (r < extend_test[s]) then
s := r + extend_offset[s]
else
s := r;
{ 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);
end
else
begin
if (r <> 15) then
break;
Inc(k, 15);
end;
Inc(k);
end;
end
else
begin
{ Section F.2.2.2: decode the AC coefficients }
{ In this path we just discard the values }
k := 1;
while (k < DCTSIZE2) do
begin
{HUFF_DECODE(s, br_state, actbl, return FALSE, label3);}
if (bits_left < HUFF_LOOKAHEAD) then
begin
if (not jpeg_fill_bit_buffer(br_state,get_buffer,bits_left, 0)) then
begin
decode_mcu := False;
exit;
end;
get_buffer := br_state.get_buffer;
bits_left := br_state.bits_left;
if (bits_left < HUFF_LOOKAHEAD) then
begin
nb := 1;
goto label3;
end;
end;
{look := PEEK_BITS(HUFF_LOOKAHEAD);}
look := int(get_buffer shr (bits_left - HUFF_LOOKAHEAD)) and
pred(1 shl HUFF_LOOKAHEAD);
nb := actbl^.look_nbits[look];
if (nb <> 0) then
begin
{DROP_BITS(nb);}
Dec(bits_left, nb);
s := actbl^.look_sym[look];
end
else
begin
nb := HUFF_LOOKAHEAD+1;
label3:
s := jpeg_huff_decode(br_state,get_buffer,bits_left,actbl,nb);
if (s < 0) then
begin
decode_mcu := FALSE;
exit;
end;
get_buffer := br_state.get_buffer;
bits_left := br_state.bits_left;
end;
r := s shr 4;
s := s and 15;
if (s <> 0) then
begin
Inc(k, r);
{CHECK_BIT_BUFFER(br_state, s, return FALSE);}
if (bits_left < s) then
begin
if (not jpeg_fill_bit_buffer(br_state,get_buffer,bits_left,s)) then
begin
decode_mcu := FALSE;
exit;
end;
get_buffer := br_state.get_buffer;
bits_left := br_state.bits_left;
end;
{DROP_BITS(s);}
Dec(bits_left, s);
end
else
begin
if (r <> 15) then
break;
Inc(k, 15);
end;
Inc(k);
end;
end;
end;
{ Completed MCU, so update state }
{BITREAD_SAVE_STATE(cinfo,entropy^.bitstate);}
cinfo^.src^.next_input_byte := br_state.next_input_byte;
cinfo^.src^.bytes_in_buffer := br_state.bytes_in_buffer;
entropy^.bitstate.get_buffer := get_buffer;
entropy^.bitstate.bits_left := bits_left;
{ASSIGN_STATE(entropy^.saved, state);}
entropy^.saved := state;
end;
{ Account for restart interval (no-op if not using restarts) }
Dec(entropy^.restarts_to_go);
decode_mcu := TRUE;
end;
{ Module initialization routine for Huffman entropy decoding. }
{GLOBAL}
procedure jinit_huff_decoder (cinfo : j_decompress_ptr);
var
entropy : huff_entropy_ptr;
i : int;
begin
entropy := huff_entropy_ptr(
cinfo^.mem^.alloc_small (j_common_ptr(cinfo), JPOOL_IMAGE,
SIZEOF(huff_entropy_decoder)) );
cinfo^.entropy := jpeg_entropy_decoder_ptr (entropy);
entropy^.pub.start_pass := start_pass_huff_decoder;
entropy^.pub.decode_mcu := decode_mcu;
{ Mark tables unallocated }
for i := 0 to pred(NUM_HUFF_TBLS) do
begin
entropy^.dc_derived_tbls[i] := NIL;
entropy^.ac_derived_tbls[i] := NIL;
end;
end;
end.
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