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jchuff.c
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jchuff.c
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/*
* jchuff.c
*
* This file was part of the Independent JPEG Group's software:
* Copyright (C) 1991-1997, Thomas G. Lane.
* libjpeg-turbo Modifications:
* Copyright (C) 2009-2011, 2014-2016, 2018-2020, D. R. Commander.
* Copyright (C) 2015, Matthieu Darbois.
* Copyright (C) 2018, Matthias Räncker.
* Copyright (C) 2020, Arm Limited.
* For conditions of distribution and use, see the accompanying README.ijg
* file.
*
* This file contains Huffman entropy encoding routines.
*
* Much of the complexity here has to do with supporting output suspension.
* If the data destination 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 JPEG objects only upon successful completion of an MCU.
*
* NOTE: All referenced figures are from
* Recommendation ITU-T T.81 (1992) | ISO/IEC 10918-1:1994.
*/
#define JPEG_INTERNALS
#include "jinclude.h"
#include "jpeglib.h"
#include "jsimd.h"
#include "jconfigint.h"
#include <limits.h>
/*
* NOTE: If USE_CLZ_INTRINSIC is defined, then clz/bsr instructions will be
* used for bit counting rather than the lookup table. This will reduce the
* memory footprint by 64k, which is important for some mobile applications
* that create many isolated instances of libjpeg-turbo (web browsers, for
* instance.) This may improve performance on some mobile platforms as well.
* This feature is enabled by default only on Arm processors, because some x86
* chips have a slow implementation of bsr, and the use of clz/bsr cannot be
* shown to have a significant performance impact even on the x86 chips that
* have a fast implementation of it. When building for Armv6, you can
* explicitly disable the use of clz/bsr by adding -mthumb to the compiler
* flags (this defines __thumb__).
*/
#if defined(__arm__) || defined(__aarch64__) || defined(_M_ARM) || \
defined(_M_ARM64)
#if !defined(__thumb__) || defined(__thumb2__)
#define USE_CLZ_INTRINSIC
#endif
#endif
#ifdef USE_CLZ_INTRINSIC
#if defined(_MSC_VER) && !defined(__clang__)
#define JPEG_NBITS_NONZERO(x) (32 - _CountLeadingZeros(x))
#else
#define JPEG_NBITS_NONZERO(x) (32 - __builtin_clz(x))
#endif
#define JPEG_NBITS(x) (x ? JPEG_NBITS_NONZERO(x) : 0)
#else
#include "jpeg_nbits_table.h"
#define JPEG_NBITS(x) (jpeg_nbits_table[x])
#define JPEG_NBITS_NONZERO(x) JPEG_NBITS(x)
#endif
/* Expanded entropy encoder object for Huffman encoding.
*
* The savable_state subrecord contains fields that change within an MCU,
* but must not be updated permanently until we complete the MCU.
*/
#if defined(__x86_64__) && defined(__ILP32__)
typedef unsigned long long bit_buf_type;
#else
typedef size_t bit_buf_type;
#endif
/* NOTE: The more optimal Huffman encoding algorithm is only used by the
* intrinsics implementation of the Arm Neon SIMD extensions, which is why we
* retain the old Huffman encoder behavior when using the GAS implementation.
*/
#if defined(WITH_SIMD) && !(defined(__arm__) || defined(__aarch64__) || \
defined(_M_ARM) || defined(_M_ARM64))
typedef unsigned long long simd_bit_buf_type;
#else
typedef bit_buf_type simd_bit_buf_type;
#endif
#if (defined(SIZEOF_SIZE_T) && SIZEOF_SIZE_T == 8) || defined(_WIN64) || \
(defined(__x86_64__) && defined(__ILP32__))
#define BIT_BUF_SIZE 64
#elif (defined(SIZEOF_SIZE_T) && SIZEOF_SIZE_T == 4) || defined(_WIN32)
#define BIT_BUF_SIZE 32
#else
#error Cannot determine word size
#endif
#define SIMD_BIT_BUF_SIZE (sizeof(simd_bit_buf_type) * 8)
typedef struct {
union {
bit_buf_type c;
simd_bit_buf_type simd;
} put_buffer; /* current bit accumulation buffer */
int free_bits; /* # of bits available in it */
/* (Neon GAS: # of bits now in it) */
int last_dc_val[MAX_COMPS_IN_SCAN]; /* last DC coef for each component */
} savable_state;
typedef struct {
struct jpeg_entropy_encoder pub; /* public fields */
savable_state saved; /* Bit buffer & DC state at start of MCU */
/* These fields are NOT loaded into local working state. */
unsigned int restarts_to_go; /* MCUs left in this restart interval */
int next_restart_num; /* next restart number to write (0-7) */
/* Pointers to derived tables (these workspaces have image lifespan) */
c_derived_tbl *dc_derived_tbls[NUM_HUFF_TBLS];
c_derived_tbl *ac_derived_tbls[NUM_HUFF_TBLS];
#ifdef ENTROPY_OPT_SUPPORTED /* Statistics tables for optimization */
long *dc_count_ptrs[NUM_HUFF_TBLS];
long *ac_count_ptrs[NUM_HUFF_TBLS];
#endif
int simd;
} huff_entropy_encoder;
typedef huff_entropy_encoder *huff_entropy_ptr;
/* Working state while writing an MCU.
* This struct contains all the fields that are needed by subroutines.
*/
typedef struct {
JOCTET *next_output_byte; /* => next byte to write in buffer */
size_t free_in_buffer; /* # of byte spaces remaining in buffer */
savable_state cur; /* Current bit buffer & DC state */
j_compress_ptr cinfo; /* dump_buffer needs access to this */
int simd;
} working_state;
/* Forward declarations */
METHODDEF(boolean) encode_mcu_huff(j_compress_ptr cinfo, JBLOCKROW *MCU_data);
METHODDEF(void) finish_pass_huff(j_compress_ptr cinfo);
#ifdef ENTROPY_OPT_SUPPORTED
METHODDEF(boolean) encode_mcu_gather(j_compress_ptr cinfo,
JBLOCKROW *MCU_data);
METHODDEF(void) finish_pass_gather(j_compress_ptr cinfo);
#endif
/*
* Initialize for a Huffman-compressed scan.
* If gather_statistics is TRUE, we do not output anything during the scan,
* just count the Huffman symbols used and generate Huffman code tables.
*/
METHODDEF(void)
start_pass_huff(j_compress_ptr cinfo, boolean gather_statistics)
{
huff_entropy_ptr entropy = (huff_entropy_ptr)cinfo->entropy;
int ci, dctbl, actbl;
jpeg_component_info *compptr;
if (gather_statistics) {
#ifdef ENTROPY_OPT_SUPPORTED
entropy->pub.encode_mcu = encode_mcu_gather;
entropy->pub.finish_pass = finish_pass_gather;
#else
ERREXIT(cinfo, JERR_NOT_COMPILED);
#endif
} else {
entropy->pub.encode_mcu = encode_mcu_huff;
entropy->pub.finish_pass = finish_pass_huff;
}
entropy->simd = jsimd_can_huff_encode_one_block();
for (ci = 0; ci < cinfo->comps_in_scan; ci++) {
compptr = cinfo->cur_comp_info[ci];
dctbl = compptr->dc_tbl_no;
actbl = compptr->ac_tbl_no;
if (gather_statistics) {
#ifdef ENTROPY_OPT_SUPPORTED
/* Check for invalid table indexes */
/* (make_c_derived_tbl does this in the other path) */
if (dctbl < 0 || dctbl >= NUM_HUFF_TBLS)
ERREXIT1(cinfo, JERR_NO_HUFF_TABLE, dctbl);
if (actbl < 0 || actbl >= NUM_HUFF_TBLS)
ERREXIT1(cinfo, JERR_NO_HUFF_TABLE, actbl);
/* Allocate and zero the statistics tables */
/* Note that jpeg_gen_optimal_table expects 257 entries in each table! */
if (entropy->dc_count_ptrs[dctbl] == NULL)
entropy->dc_count_ptrs[dctbl] = (long *)
(*cinfo->mem->alloc_small) ((j_common_ptr)cinfo, JPOOL_IMAGE,
257 * sizeof(long));
MEMZERO(entropy->dc_count_ptrs[dctbl], 257 * sizeof(long));
if (entropy->ac_count_ptrs[actbl] == NULL)
entropy->ac_count_ptrs[actbl] = (long *)
(*cinfo->mem->alloc_small) ((j_common_ptr)cinfo, JPOOL_IMAGE,
257 * sizeof(long));
MEMZERO(entropy->ac_count_ptrs[actbl], 257 * sizeof(long));
#endif
} else {
/* Compute derived values for Huffman tables */
/* We may do this more than once for a table, but it's not expensive */
jpeg_make_c_derived_tbl(cinfo, TRUE, dctbl,
&entropy->dc_derived_tbls[dctbl]);
jpeg_make_c_derived_tbl(cinfo, FALSE, actbl,
&entropy->ac_derived_tbls[actbl]);
}
/* Initialize DC predictions to 0 */
entropy->saved.last_dc_val[ci] = 0;
}
/* Initialize bit buffer to empty */
if (entropy->simd) {
entropy->saved.put_buffer.simd = 0;
#if defined(__aarch64__) && !defined(NEON_INTRINSICS)
entropy->saved.free_bits = 0;
#else
entropy->saved.free_bits = SIMD_BIT_BUF_SIZE;
#endif
} else {
entropy->saved.put_buffer.c = 0;
entropy->saved.free_bits = BIT_BUF_SIZE;
}
/* Initialize restart stuff */
entropy->restarts_to_go = cinfo->restart_interval;
entropy->next_restart_num = 0;
}
/*
* Compute the derived values for a Huffman table.
* This routine also performs some validation checks on the table.
*
* Note this is also used by jcphuff.c.
*/
GLOBAL(void)
jpeg_make_c_derived_tbl(j_compress_ptr cinfo, boolean isDC, int tblno,
c_derived_tbl **pdtbl)
{
JHUFF_TBL *htbl;
c_derived_tbl *dtbl;
int p, i, l, lastp, si, maxsymbol;
char huffsize[257];
unsigned int huffcode[257];
unsigned int code;
/* 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 || tblno >= NUM_HUFF_TBLS)
ERREXIT1(cinfo, JERR_NO_HUFF_TABLE, tblno);
htbl =
isDC ? cinfo->dc_huff_tbl_ptrs[tblno] : cinfo->ac_huff_tbl_ptrs[tblno];
if (htbl == NULL)
ERREXIT1(cinfo, JERR_NO_HUFF_TABLE, tblno);
/* Allocate a workspace if we haven't already done so. */
if (*pdtbl == NULL)
*pdtbl = (c_derived_tbl *)
(*cinfo->mem->alloc_small) ((j_common_ptr)cinfo, JPOOL_IMAGE,
sizeof(c_derived_tbl));
dtbl = *pdtbl;
/* Figure C.1: make table of Huffman code length for each symbol */
p = 0;
for (l = 1; l <= 16; l++) {
i = (int)htbl->bits[l];
if (i < 0 || p + i > 256) /* protect against table overrun */
ERREXIT(cinfo, JERR_BAD_HUFF_TABLE);
while (i--)
huffsize[p++] = (char)l;
}
huffsize[p] = 0;
lastp = 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]) {
while (((int)huffsize[p]) == si) {
huffcode[p++] = code;
code++;
}
/* 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 (((JLONG)code) >= (((JLONG)1) << si))
ERREXIT(cinfo, JERR_BAD_HUFF_TABLE);
code <<= 1;
si++;
}
/* Figure C.3: generate encoding tables */
/* These are code and size indexed by symbol value */
/* Set all codeless symbols to have code length 0;
* this lets us detect duplicate VAL entries here, and later
* allows emit_bits to detect any attempt to emit such symbols.
*/
MEMZERO(dtbl->ehufsi, sizeof(dtbl->ehufsi));
/* This is also a convenient place to check for out-of-range
* and duplicated VAL entries. We allow 0..255 for AC symbols
* but only 0..15 for DC. (We could constrain them further
* based on data depth and mode, but this seems enough.)
*/
maxsymbol = isDC ? 15 : 255;
for (p = 0; p < lastp; p++) {
i = htbl->huffval[p];
if (i < 0 || i > maxsymbol || dtbl->ehufsi[i])
ERREXIT(cinfo, JERR_BAD_HUFF_TABLE);
dtbl->ehufco[i] = huffcode[p];
dtbl->ehufsi[i] = huffsize[p];
}
}
/* Outputting bytes to the file */
/* Emit a byte, taking 'action' if must suspend. */
#define emit_byte(state, val, action) { \
*(state)->next_output_byte++ = (JOCTET)(val); \
if (--(state)->free_in_buffer == 0) \
if (!dump_buffer(state)) \
{ action; } \
}
LOCAL(boolean)
dump_buffer(working_state *state)
/* Empty the output buffer; return TRUE if successful, FALSE if must suspend */
{
struct jpeg_destination_mgr *dest = state->cinfo->dest;
if (!(*dest->empty_output_buffer) (state->cinfo))
return FALSE;
/* After a successful buffer dump, must reset buffer pointers */
state->next_output_byte = dest->next_output_byte;
state->free_in_buffer = dest->free_in_buffer;
return TRUE;
}
/* Outputting bits to the file */
/* Output byte b and, speculatively, an additional 0 byte. 0xFF must be
* encoded as 0xFF 0x00, so the output buffer pointer is advanced by 2 if the
* byte is 0xFF. Otherwise, the output buffer pointer is advanced by 1, and
* the speculative 0 byte will be overwritten by the next byte.
*/
#define EMIT_BYTE(b) { \
buffer[0] = (JOCTET)(b); \
buffer[1] = 0; \
buffer -= -2 + ((JOCTET)(b) < 0xFF); \
}
/* Output the entire bit buffer. If there are no 0xFF bytes in it, then write
* directly to the output buffer. Otherwise, use the EMIT_BYTE() macro to
* encode 0xFF as 0xFF 0x00.
*/
#if BIT_BUF_SIZE == 64
#define FLUSH() { \
if (put_buffer & 0x8080808080808080 & ~(put_buffer + 0x0101010101010101)) { \
EMIT_BYTE(put_buffer >> 56) \
EMIT_BYTE(put_buffer >> 48) \
EMIT_BYTE(put_buffer >> 40) \
EMIT_BYTE(put_buffer >> 32) \
EMIT_BYTE(put_buffer >> 24) \
EMIT_BYTE(put_buffer >> 16) \
EMIT_BYTE(put_buffer >> 8) \
EMIT_BYTE(put_buffer ) \
} else { \
buffer[0] = (JOCTET)(put_buffer >> 56); \
buffer[1] = (JOCTET)(put_buffer >> 48); \
buffer[2] = (JOCTET)(put_buffer >> 40); \
buffer[3] = (JOCTET)(put_buffer >> 32); \
buffer[4] = (JOCTET)(put_buffer >> 24); \
buffer[5] = (JOCTET)(put_buffer >> 16); \
buffer[6] = (JOCTET)(put_buffer >> 8); \
buffer[7] = (JOCTET)(put_buffer); \
buffer += 8; \
} \
}
#else
#define FLUSH() { \
if (put_buffer & 0x80808080 & ~(put_buffer + 0x01010101)) { \
EMIT_BYTE(put_buffer >> 24) \
EMIT_BYTE(put_buffer >> 16) \
EMIT_BYTE(put_buffer >> 8) \
EMIT_BYTE(put_buffer ) \
} else { \
buffer[0] = (JOCTET)(put_buffer >> 24); \
buffer[1] = (JOCTET)(put_buffer >> 16); \
buffer[2] = (JOCTET)(put_buffer >> 8); \
buffer[3] = (JOCTET)(put_buffer); \
buffer += 4; \
} \
}
#endif
/* Fill the bit buffer to capacity with the leading bits from code, then output
* the bit buffer and put the remaining bits from code into the bit buffer.
*/
#define PUT_AND_FLUSH(code, size) { \
put_buffer = (put_buffer << (size + free_bits)) | (code >> -free_bits); \
FLUSH() \
free_bits += BIT_BUF_SIZE; \
put_buffer = code; \
}
/* Insert code into the bit buffer and output the bit buffer if needed.
* NOTE: We can't flush with free_bits == 0, since the left shift in
* PUT_AND_FLUSH() would have undefined behavior.
*/
#define PUT_BITS(code, size) { \
free_bits -= size; \
if (free_bits < 0) \
PUT_AND_FLUSH(code, size) \
else \
put_buffer = (put_buffer << size) | code; \
}
#define PUT_CODE(code, size) { \
temp &= (((JLONG)1) << nbits) - 1; \
temp |= code << nbits; \
nbits += size; \
PUT_BITS(temp, nbits) \
}
/* Although it is exceedingly rare, it is possible for a Huffman-encoded
* coefficient block to be larger than the 128-byte unencoded block. For each
* of the 64 coefficients, PUT_BITS is invoked twice, and each invocation can
* theoretically store 16 bits (for a maximum of 2048 bits or 256 bytes per
* encoded block.) If, for instance, one artificially sets the AC
* coefficients to alternating values of 32767 and -32768 (using the JPEG
* scanning order-- 1, 8, 16, etc.), then this will produce an encoded block
* larger than 200 bytes.
*/
#define BUFSIZE (DCTSIZE2 * 8)
#define LOAD_BUFFER() { \
if (state->free_in_buffer < BUFSIZE) { \
localbuf = 1; \
buffer = _buffer; \
} else \
buffer = state->next_output_byte; \
}
#define STORE_BUFFER() { \
if (localbuf) { \
size_t bytes, bytestocopy; \
bytes = buffer - _buffer; \
buffer = _buffer; \
while (bytes > 0) { \
bytestocopy = MIN(bytes, state->free_in_buffer); \
MEMCOPY(state->next_output_byte, buffer, bytestocopy); \
state->next_output_byte += bytestocopy; \
buffer += bytestocopy; \
state->free_in_buffer -= bytestocopy; \
if (state->free_in_buffer == 0) \
if (!dump_buffer(state)) return FALSE; \
bytes -= bytestocopy; \
} \
} else { \
state->free_in_buffer -= (buffer - state->next_output_byte); \
state->next_output_byte = buffer; \
} \
}
LOCAL(boolean)
flush_bits(working_state *state)
{
JOCTET _buffer[BUFSIZE], *buffer, temp;
simd_bit_buf_type put_buffer; int put_bits;
int localbuf = 0;
if (state->simd) {
#if defined(__aarch64__) && !defined(NEON_INTRINSICS)
put_bits = state->cur.free_bits;
#else
put_bits = SIMD_BIT_BUF_SIZE - state->cur.free_bits;
#endif
put_buffer = state->cur.put_buffer.simd;
} else {
put_bits = BIT_BUF_SIZE - state->cur.free_bits;
put_buffer = state->cur.put_buffer.c;
}
LOAD_BUFFER()
while (put_bits >= 8) {
put_bits -= 8;
temp = (JOCTET)(put_buffer >> put_bits);
EMIT_BYTE(temp)
}
if (put_bits) {
/* fill partial byte with ones */
temp = (JOCTET)((put_buffer << (8 - put_bits)) | (0xFF >> put_bits));
EMIT_BYTE(temp)
}
if (state->simd) { /* and reset bit buffer to empty */
state->cur.put_buffer.simd = 0;
#if defined(__aarch64__) && !defined(NEON_INTRINSICS)
state->cur.free_bits = 0;
#else
state->cur.free_bits = SIMD_BIT_BUF_SIZE;
#endif
} else {
state->cur.put_buffer.c = 0;
state->cur.free_bits = BIT_BUF_SIZE;
}
STORE_BUFFER()
return TRUE;
}
/* Encode a single block's worth of coefficients */
LOCAL(boolean)
encode_one_block_simd(working_state *state, JCOEFPTR block, int last_dc_val,
c_derived_tbl *dctbl, c_derived_tbl *actbl)
{
JOCTET _buffer[BUFSIZE], *buffer;
int localbuf = 0;
LOAD_BUFFER()
buffer = jsimd_huff_encode_one_block(state, buffer, block, last_dc_val,
dctbl, actbl);
STORE_BUFFER()
return TRUE;
}
LOCAL(boolean)
encode_one_block(working_state *state, JCOEFPTR block, int last_dc_val,
c_derived_tbl *dctbl, c_derived_tbl *actbl)
{
int temp, nbits, free_bits;
bit_buf_type put_buffer;
JOCTET _buffer[BUFSIZE], *buffer;
int localbuf = 0;
free_bits = state->cur.free_bits;
put_buffer = state->cur.put_buffer.c;
LOAD_BUFFER()
/* Encode the DC coefficient difference per section F.1.2.1 */
temp = block[0] - last_dc_val;
/* This is a well-known technique for obtaining the absolute value without a
* branch. It is derived from an assembly language technique presented in
* "How to Optimize for the Pentium Processors", Copyright (c) 1996, 1997 by
* Agner Fog. This code assumes we are on a two's complement machine.
*/
nbits = temp >> (CHAR_BIT * sizeof(int) - 1);
temp += nbits;
nbits ^= temp;
/* Find the number of bits needed for the magnitude of the coefficient */
nbits = JPEG_NBITS(nbits);
/* Emit the Huffman-coded symbol for the number of bits.
* Emit that number of bits of the value, if positive,
* or the complement of its magnitude, if negative.
*/
PUT_CODE(dctbl->ehufco[nbits], dctbl->ehufsi[nbits])
/* Encode the AC coefficients per section F.1.2.2 */
{
int r = 0; /* r = run length of zeros */
/* Manually unroll the k loop to eliminate the counter variable. This
* improves performance greatly on systems with a limited number of
* registers (such as x86.)
*/
#define kloop(jpeg_natural_order_of_k) { \
if ((temp = block[jpeg_natural_order_of_k]) == 0) { \
r += 16; \
} else { \
/* Branch-less absolute value, bitwise complement, etc., same as above */ \
nbits = temp >> (CHAR_BIT * sizeof(int) - 1); \
temp += nbits; \
nbits ^= temp; \
nbits = JPEG_NBITS_NONZERO(nbits); \
/* if run length > 15, must emit special run-length-16 codes (0xF0) */ \
while (r >= 16 * 16) { \
r -= 16 * 16; \
PUT_BITS(actbl->ehufco[0xf0], actbl->ehufsi[0xf0]) \
} \
/* Emit Huffman symbol for run length / number of bits */ \
r += nbits; \
PUT_CODE(actbl->ehufco[r], actbl->ehufsi[r]) \
r = 0; \
} \
}
/* One iteration for each value in jpeg_natural_order[] */
kloop(1); kloop(8); kloop(16); kloop(9); kloop(2); kloop(3);
kloop(10); kloop(17); kloop(24); kloop(32); kloop(25); kloop(18);
kloop(11); kloop(4); kloop(5); kloop(12); kloop(19); kloop(26);
kloop(33); kloop(40); kloop(48); kloop(41); kloop(34); kloop(27);
kloop(20); kloop(13); kloop(6); kloop(7); kloop(14); kloop(21);
kloop(28); kloop(35); kloop(42); kloop(49); kloop(56); kloop(57);
kloop(50); kloop(43); kloop(36); kloop(29); kloop(22); kloop(15);
kloop(23); kloop(30); kloop(37); kloop(44); kloop(51); kloop(58);
kloop(59); kloop(52); kloop(45); kloop(38); kloop(31); kloop(39);
kloop(46); kloop(53); kloop(60); kloop(61); kloop(54); kloop(47);
kloop(55); kloop(62); kloop(63);
/* If the last coef(s) were zero, emit an end-of-block code */
if (r > 0) {
PUT_BITS(actbl->ehufco[0], actbl->ehufsi[0])
}
}
state->cur.put_buffer.c = put_buffer;
state->cur.free_bits = free_bits;
STORE_BUFFER()
return TRUE;
}
/*
* Emit a restart marker & resynchronize predictions.
*/
LOCAL(boolean)
emit_restart(working_state *state, int restart_num)
{
int ci;
if (!flush_bits(state))
return FALSE;
emit_byte(state, 0xFF, return FALSE);
emit_byte(state, JPEG_RST0 + restart_num, return FALSE);
/* Re-initialize DC predictions to 0 */
for (ci = 0; ci < state->cinfo->comps_in_scan; ci++)
state->cur.last_dc_val[ci] = 0;
/* The restart counter is not updated until we successfully write the MCU. */
return TRUE;
}
/*
* Encode and output one MCU's worth of Huffman-compressed coefficients.
*/
METHODDEF(boolean)
encode_mcu_huff(j_compress_ptr cinfo, JBLOCKROW *MCU_data)
{
huff_entropy_ptr entropy = (huff_entropy_ptr)cinfo->entropy;
working_state state;
int blkn, ci;
jpeg_component_info *compptr;
/* Load up working state */
state.next_output_byte = cinfo->dest->next_output_byte;
state.free_in_buffer = cinfo->dest->free_in_buffer;
state.cur = entropy->saved;
state.cinfo = cinfo;
state.simd = entropy->simd;
/* Emit restart marker if needed */
if (cinfo->restart_interval) {
if (entropy->restarts_to_go == 0)
if (!emit_restart(&state, entropy->next_restart_num))
return FALSE;
}
/* Encode the MCU data blocks */
if (entropy->simd) {
for (blkn = 0; blkn < cinfo->blocks_in_MCU; blkn++) {
ci = cinfo->MCU_membership[blkn];
compptr = cinfo->cur_comp_info[ci];
if (!encode_one_block_simd(&state,
MCU_data[blkn][0], state.cur.last_dc_val[ci],
entropy->dc_derived_tbls[compptr->dc_tbl_no],
entropy->ac_derived_tbls[compptr->ac_tbl_no]))
return FALSE;
/* Update last_dc_val */
state.cur.last_dc_val[ci] = MCU_data[blkn][0][0];
}
} else {
for (blkn = 0; blkn < cinfo->blocks_in_MCU; blkn++) {
ci = cinfo->MCU_membership[blkn];
compptr = cinfo->cur_comp_info[ci];
if (!encode_one_block(&state,
MCU_data[blkn][0], state.cur.last_dc_val[ci],
entropy->dc_derived_tbls[compptr->dc_tbl_no],
entropy->ac_derived_tbls[compptr->ac_tbl_no]))
return FALSE;
/* Update last_dc_val */
state.cur.last_dc_val[ci] = MCU_data[blkn][0][0];
}
}
/* Completed MCU, so update state */
cinfo->dest->next_output_byte = state.next_output_byte;
cinfo->dest->free_in_buffer = state.free_in_buffer;
entropy->saved = state.cur;
/* Update restart-interval state too */
if (cinfo->restart_interval) {
if (entropy->restarts_to_go == 0) {
entropy->restarts_to_go = cinfo->restart_interval;
entropy->next_restart_num++;
entropy->next_restart_num &= 7;
}
entropy->restarts_to_go--;
}
return TRUE;
}
/*
* Finish up at the end of a Huffman-compressed scan.
*/
METHODDEF(void)
finish_pass_huff(j_compress_ptr cinfo)
{
huff_entropy_ptr entropy = (huff_entropy_ptr)cinfo->entropy;
working_state state;
/* Load up working state ... flush_bits needs it */
state.next_output_byte = cinfo->dest->next_output_byte;
state.free_in_buffer = cinfo->dest->free_in_buffer;
state.cur = entropy->saved;
state.cinfo = cinfo;
state.simd = entropy->simd;
/* Flush out the last data */
if (!flush_bits(&state))
ERREXIT(cinfo, JERR_CANT_SUSPEND);
/* Update state */
cinfo->dest->next_output_byte = state.next_output_byte;
cinfo->dest->free_in_buffer = state.free_in_buffer;
entropy->saved = state.cur;
}
/*
* Huffman coding optimization.
*
* We first scan the supplied data and count the number of uses of each symbol
* that is to be Huffman-coded. (This process MUST agree with the code above.)
* Then we build a Huffman coding tree for the observed counts.
* Symbols which are not needed at all for the particular image are not
* assigned any code, which saves space in the DHT marker as well as in
* the compressed data.
*/
#ifdef ENTROPY_OPT_SUPPORTED
/* Process a single block's worth of coefficients */
LOCAL(void)
htest_one_block(j_compress_ptr cinfo, JCOEFPTR block, int last_dc_val,
long dc_counts[], long ac_counts[])
{
register int temp;
register int nbits;
register int k, r;
/* Encode the DC coefficient difference per section F.1.2.1 */
temp = block[0] - last_dc_val;
if (temp < 0)
temp = -temp;
/* Find the number of bits needed for the magnitude of the coefficient */
nbits = 0;
while (temp) {
nbits++;
temp >>= 1;
}
/* Check for out-of-range coefficient values.
* Since we're encoding a difference, the range limit is twice as much.
*/
if (nbits > MAX_COEF_BITS + 1)
ERREXIT(cinfo, JERR_BAD_DCT_COEF);
/* Count the Huffman symbol for the number of bits */
dc_counts[nbits]++;
/* Encode the AC coefficients per section F.1.2.2 */
r = 0; /* r = run length of zeros */
for (k = 1; k < DCTSIZE2; k++) {
if ((temp = block[jpeg_natural_order[k]]) == 0) {
r++;
} else {
/* if run length > 15, must emit special run-length-16 codes (0xF0) */
while (r > 15) {
ac_counts[0xF0]++;
r -= 16;
}
/* Find the number of bits needed for the magnitude of the coefficient */
if (temp < 0)
temp = -temp;
/* Find the number of bits needed for the magnitude of the coefficient */
nbits = 1; /* there must be at least one 1 bit */
while ((temp >>= 1))
nbits++;
/* Check for out-of-range coefficient values */
if (nbits > MAX_COEF_BITS)
ERREXIT(cinfo, JERR_BAD_DCT_COEF);
/* Count Huffman symbol for run length / number of bits */
ac_counts[(r << 4) + nbits]++;
r = 0;
}
}
/* If the last coef(s) were zero, emit an end-of-block code */
if (r > 0)
ac_counts[0]++;
}
/*
* Trial-encode one MCU's worth of Huffman-compressed coefficients.
* No data is actually output, so no suspension return is possible.
*/
METHODDEF(boolean)
encode_mcu_gather(j_compress_ptr cinfo, JBLOCKROW *MCU_data)
{
huff_entropy_ptr entropy = (huff_entropy_ptr)cinfo->entropy;
int blkn, ci;
jpeg_component_info *compptr;
/* Take care of restart intervals if needed */
if (cinfo->restart_interval) {
if (entropy->restarts_to_go == 0) {
/* Re-initialize DC predictions to 0 */
for (ci = 0; ci < cinfo->comps_in_scan; ci++)
entropy->saved.last_dc_val[ci] = 0;
/* Update restart state */
entropy->restarts_to_go = cinfo->restart_interval;
}
entropy->restarts_to_go--;
}
for (blkn = 0; blkn < cinfo->blocks_in_MCU; blkn++) {
ci = cinfo->MCU_membership[blkn];
compptr = cinfo->cur_comp_info[ci];
htest_one_block(cinfo, MCU_data[blkn][0], entropy->saved.last_dc_val[ci],
entropy->dc_count_ptrs[compptr->dc_tbl_no],
entropy->ac_count_ptrs[compptr->ac_tbl_no]);
entropy->saved.last_dc_val[ci] = MCU_data[blkn][0][0];
}
return TRUE;
}
/*
* Generate the best Huffman code table for the given counts, fill htbl.
* Note this is also used by jcphuff.c.
*
* The JPEG standard requires that no symbol be assigned a codeword of all
* one bits (so that padding bits added at the end of a compressed segment
* can't look like a valid code). Because of the canonical ordering of
* codewords, this just means that there must be an unused slot in the
* longest codeword length category. Annex K (Clause K.2) of
* Rec. ITU-T T.81 (1992) | ISO/IEC 10918-1:1994 suggests reserving such a slot
* by pretending that symbol 256 is a valid symbol with count 1. In theory
* that's not optimal; giving it count zero but including it in the symbol set
* anyway should give a better Huffman code. But the theoretically better code
* actually seems to come out worse in practice, because it produces more
* all-ones bytes (which incur stuffed zero bytes in the final file). In any
* case the difference is tiny.
*
* The JPEG standard requires Huffman codes to be no more than 16 bits long.
* If some symbols have a very small but nonzero probability, the Huffman tree
* must be adjusted to meet the code length restriction. We currently use
* the adjustment method suggested in JPEG section K.2. This method is *not*
* optimal; it may not choose the best possible limited-length code. But
* typically only very-low-frequency symbols will be given less-than-optimal
* lengths, so the code is almost optimal. Experimental comparisons against
* an optimal limited-length-code algorithm indicate that the difference is
* microscopic --- usually less than a hundredth of a percent of total size.
* So the extra complexity of an optimal algorithm doesn't seem worthwhile.
*/
GLOBAL(void)
jpeg_gen_optimal_table(j_compress_ptr cinfo, JHUFF_TBL *htbl, long freq[])
{
#define MAX_CLEN 32 /* assumed maximum initial code length */
UINT8 bits[MAX_CLEN + 1]; /* bits[k] = # of symbols with code length k */
int codesize[257]; /* codesize[k] = code length of symbol k */
int others[257]; /* next symbol in current branch of tree */
int c1, c2;
int p, i, j;
long v;
/* This algorithm is explained in section K.2 of the JPEG standard */
MEMZERO(bits, sizeof(bits));
MEMZERO(codesize, sizeof(codesize));
for (i = 0; i < 257; i++)
others[i] = -1; /* init links to empty */
freq[256] = 1; /* make sure 256 has a nonzero count */
/* Including the pseudo-symbol 256 in the Huffman procedure guarantees
* that no real symbol is given code-value of all ones, because 256
* will be placed last in the largest codeword category.
*/
/* Huffman's basic algorithm to assign optimal code lengths to symbols */
for (;;) {
/* Find the smallest nonzero frequency, set c1 = its symbol */
/* In case of ties, take the larger symbol number */
c1 = -1;
v = 1000000000L;
for (i = 0; i <= 256; i++) {
if (freq[i] && freq[i] <= v) {
v = freq[i];
c1 = i;
}
}
/* Find the next smallest nonzero frequency, set c2 = its symbol */
/* In case of ties, take the larger symbol number */
c2 = -1;
v = 1000000000L;
for (i = 0; i <= 256; i++) {
if (freq[i] && freq[i] <= v && i != c1) {
v = freq[i];
c2 = i;
}
}
/* Done if we've merged everything into one frequency */
if (c2 < 0)
break;
/* Else merge the two counts/trees */
freq[c1] += freq[c2];
freq[c2] = 0;
/* Increment the codesize of everything in c1's tree branch */
codesize[c1]++;
while (others[c1] >= 0) {
c1 = others[c1];
codesize[c1]++;
}
others[c1] = c2; /* chain c2 onto c1's tree branch */
/* Increment the codesize of everything in c2's tree branch */
codesize[c2]++;
while (others[c2] >= 0) {
c2 = others[c2];
codesize[c2]++;
}