mirror of
https://github.com/LadybirdBrowser/ladybird.git
synced 2025-09-20 00:08:55 +00:00
LibGfx: Move QMArithmeticDecoder to its own file
It will be used by the JPEG2000 decoder as well. Pure code move, no behavior change.
This commit is contained in:
Nico Weber
Andreas Kling
parent
5ff75ce5fb
commit
ea441fea95
Notes:
sideshowbarker
2024-07-17 01:21:02 +09:00
Author: https://github.com/nico
Commit: ea441fea95
Pull-request: https://github.com/SerenityOS/serenity/pull/24017
7 changed files with 282 additions and 253 deletions
|
|
@ -87,6 +87,7 @@ shared_library("LibGfx") {
|
||||||
"ImageFormats/PNGWriter.cpp",
|
"ImageFormats/PNGWriter.cpp",
|
||||||
"ImageFormats/PPMLoader.cpp",
|
"ImageFormats/PPMLoader.cpp",
|
||||||
"ImageFormats/PortableFormatWriter.cpp",
|
"ImageFormats/PortableFormatWriter.cpp",
|
||||||
|
"ImageFormats/QMArithmeticDecoder.cpp",
|
||||||
"ImageFormats/QOILoader.cpp",
|
"ImageFormats/QOILoader.cpp",
|
||||||
"ImageFormats/QOIWriter.cpp",
|
"ImageFormats/QOIWriter.cpp",
|
||||||
"ImageFormats/TGALoader.cpp",
|
"ImageFormats/TGALoader.cpp",
|
||||||
|
|
|
||||||
|
|
@ -22,6 +22,7 @@
|
||||||
#include <LibGfx/ImageFormats/PGMLoader.h>
|
#include <LibGfx/ImageFormats/PGMLoader.h>
|
||||||
#include <LibGfx/ImageFormats/PNGLoader.h>
|
#include <LibGfx/ImageFormats/PNGLoader.h>
|
||||||
#include <LibGfx/ImageFormats/PPMLoader.h>
|
#include <LibGfx/ImageFormats/PPMLoader.h>
|
||||||
|
#include <LibGfx/ImageFormats/QMArithmeticDecoder.h>
|
||||||
#include <LibGfx/ImageFormats/TGALoader.h>
|
#include <LibGfx/ImageFormats/TGALoader.h>
|
||||||
#include <LibGfx/ImageFormats/TIFFLoader.h>
|
#include <LibGfx/ImageFormats/TIFFLoader.h>
|
||||||
#include <LibGfx/ImageFormats/TinyVGLoader.h>
|
#include <LibGfx/ImageFormats/TinyVGLoader.h>
|
||||||
|
|
|
||||||
|
|
@ -60,6 +60,7 @@ set(SOURCES
|
||||||
ImageFormats/PortableFormatWriter.cpp
|
ImageFormats/PortableFormatWriter.cpp
|
||||||
ImageFormats/PAMLoader.cpp
|
ImageFormats/PAMLoader.cpp
|
||||||
ImageFormats/PPMLoader.cpp
|
ImageFormats/PPMLoader.cpp
|
||||||
|
ImageFormats/QMArithmeticDecoder.cpp
|
||||||
ImageFormats/QOILoader.cpp
|
ImageFormats/QOILoader.cpp
|
||||||
ImageFormats/QOIWriter.cpp
|
ImageFormats/QOIWriter.cpp
|
||||||
ImageFormats/TGALoader.cpp
|
ImageFormats/TGALoader.cpp
|
||||||
|
|
|
||||||
|
|
@ -8,6 +8,7 @@
|
||||||
#include <AK/Utf16View.h>
|
#include <AK/Utf16View.h>
|
||||||
#include <LibGfx/ImageFormats/CCITTDecoder.h>
|
#include <LibGfx/ImageFormats/CCITTDecoder.h>
|
||||||
#include <LibGfx/ImageFormats/JBIG2Loader.h>
|
#include <LibGfx/ImageFormats/JBIG2Loader.h>
|
||||||
|
#include <LibGfx/ImageFormats/QMArithmeticDecoder.h>
|
||||||
#include <LibTextCodec/Decoder.h>
|
#include <LibTextCodec/Decoder.h>
|
||||||
|
|
||||||
// Spec: ITU-T_T_88__08_2018.pdf in the zip file here:
|
// Spec: ITU-T_T_88__08_2018.pdf in the zip file here:
|
||||||
|
|
@ -27,203 +28,6 @@
|
||||||
|
|
||||||
namespace Gfx {
|
namespace Gfx {
|
||||||
|
|
||||||
// Table E.1 – Qe values and probability estimation process
|
|
||||||
// See also E.1.2 Coding conventions and approximations
|
|
||||||
// and E.2.5 Probability estimation.
|
|
||||||
struct QeEntry {
|
|
||||||
u16 qe; // Sub-interval for the less probable symbol.
|
|
||||||
u16 nmps; // Next index if the more probable symbol is decoded
|
|
||||||
u16 nlps; // Next index if the less probable symbol is decoded
|
|
||||||
u16 switch_flag; // See second-to-last paragraph in E.1.2.
|
|
||||||
};
|
|
||||||
constexpr auto qe_table = to_array<QeEntry>({
|
|
||||||
{ 0x5601, 1, 1, 1 },
|
|
||||||
{ 0x3401, 2, 6, 0 },
|
|
||||||
{ 0x1801, 3, 9, 0 },
|
|
||||||
{ 0x0AC1, 4, 12, 0 },
|
|
||||||
{ 0x0521, 5, 29, 0 },
|
|
||||||
{ 0x0221, 38, 33, 0 },
|
|
||||||
{ 0x5601, 7, 6, 1 },
|
|
||||||
{ 0x5401, 8, 14, 0 },
|
|
||||||
{ 0x4801, 9, 14, 0 },
|
|
||||||
{ 0x3801, 10, 14, 0 },
|
|
||||||
{ 0x3001, 11, 17, 0 },
|
|
||||||
{ 0x2401, 12, 18, 0 },
|
|
||||||
{ 0x1C01, 13, 20, 0 },
|
|
||||||
{ 0x1601, 29, 21, 0 },
|
|
||||||
{ 0x5601, 15, 14, 1 },
|
|
||||||
{ 0x5401, 16, 14, 0 },
|
|
||||||
{ 0x5101, 17, 15, 0 },
|
|
||||||
{ 0x4801, 18, 16, 0 },
|
|
||||||
{ 0x3801, 19, 17, 0 },
|
|
||||||
{ 0x3401, 20, 18, 0 },
|
|
||||||
{ 0x3001, 21, 19, 0 },
|
|
||||||
{ 0x2801, 22, 19, 0 },
|
|
||||||
{ 0x2401, 23, 20, 0 },
|
|
||||||
{ 0x2201, 24, 21, 0 },
|
|
||||||
{ 0x1C01, 25, 22, 0 },
|
|
||||||
{ 0x1801, 26, 23, 0 },
|
|
||||||
{ 0x1601, 27, 24, 0 },
|
|
||||||
{ 0x1401, 28, 25, 0 },
|
|
||||||
{ 0x1201, 29, 26, 0 },
|
|
||||||
{ 0x1101, 30, 27, 0 },
|
|
||||||
{ 0x0AC1, 31, 28, 0 },
|
|
||||||
{ 0x09C1, 32, 29, 0 },
|
|
||||||
{ 0x08A1, 33, 30, 0 },
|
|
||||||
{ 0x0521, 34, 31, 0 },
|
|
||||||
{ 0x0441, 35, 32, 0 },
|
|
||||||
{ 0x02A1, 36, 33, 0 },
|
|
||||||
{ 0x0221, 37, 34, 0 },
|
|
||||||
{ 0x0141, 38, 35, 0 },
|
|
||||||
{ 0x0111, 39, 36, 0 },
|
|
||||||
{ 0x0085, 40, 37, 0 },
|
|
||||||
{ 0x0049, 41, 38, 0 },
|
|
||||||
{ 0x0025, 42, 39, 0 },
|
|
||||||
{ 0x0015, 43, 40, 0 },
|
|
||||||
{ 0x0009, 44, 41, 0 },
|
|
||||||
{ 0x0005, 45, 42, 0 },
|
|
||||||
{ 0x0001, 45, 43, 0 },
|
|
||||||
{ 0x5601, 46, 46, 0 },
|
|
||||||
});
|
|
||||||
|
|
||||||
ErrorOr<QMArithmeticDecoder> QMArithmeticDecoder::initialize(ReadonlyBytes data)
|
|
||||||
{
|
|
||||||
QMArithmeticDecoder decoder { data };
|
|
||||||
decoder.INITDEC();
|
|
||||||
return decoder;
|
|
||||||
}
|
|
||||||
|
|
||||||
bool QMArithmeticDecoder::get_next_bit(Context& context)
|
|
||||||
{
|
|
||||||
CX = &context;
|
|
||||||
// Useful for comparing to Table H.1 – Encoder and decoder trace data.
|
|
||||||
// dbg("I={} MPS={} A={:#x} C={:#x} CT={} B={:#x}", I(CX), MPS(CX), A, C, CT, B());
|
|
||||||
u8 D = DECODE();
|
|
||||||
// dbgln(" -> D={}", D);
|
|
||||||
return D;
|
|
||||||
}
|
|
||||||
|
|
||||||
u16 QMArithmeticDecoder::Qe(u16 index) { return qe_table[index].qe; }
|
|
||||||
u8 QMArithmeticDecoder::NMPS(u16 index) { return qe_table[index].nmps; }
|
|
||||||
u8 QMArithmeticDecoder::NLPS(u16 index) { return qe_table[index].nlps; }
|
|
||||||
u8 QMArithmeticDecoder::SWITCH(u16 index) { return qe_table[index].switch_flag; }
|
|
||||||
|
|
||||||
u8 QMArithmeticDecoder::B(size_t offset) const
|
|
||||||
{
|
|
||||||
// E.2.10 Minimization of the compressed data
|
|
||||||
// "the convention is used in the decoder that when a marker code is encountered,
|
|
||||||
// 1-bits (without bit stuffing) are supplied to the decoder until the coding interval is complete."
|
|
||||||
if (BP + offset >= m_data.size())
|
|
||||||
return 0xFF;
|
|
||||||
return m_data[BP + offset];
|
|
||||||
}
|
|
||||||
|
|
||||||
void QMArithmeticDecoder::INITDEC()
|
|
||||||
{
|
|
||||||
// E.3.5 Initialization of the decoder (INITDEC)
|
|
||||||
// Figure G.1 – Initialization of the software conventions decoder
|
|
||||||
|
|
||||||
// "BP, the pointer to the compressed data, is initialized to BPST (pointing to the first compressed byte)."
|
|
||||||
auto const BPST = 0;
|
|
||||||
BP = BPST;
|
|
||||||
C = (B() ^ 0xFF) << 16;
|
|
||||||
|
|
||||||
BYTEIN();
|
|
||||||
|
|
||||||
C = C << 7;
|
|
||||||
CT = CT - 7;
|
|
||||||
A = 0x8000;
|
|
||||||
}
|
|
||||||
|
|
||||||
u8 QMArithmeticDecoder::DECODE()
|
|
||||||
{
|
|
||||||
// E.3.2 Decoding a decision (DECODE)
|
|
||||||
// Figure G.2 – Decoding an MPS or an LPS in the software-conventions decoder
|
|
||||||
u8 D;
|
|
||||||
A = A - Qe(I(CX));
|
|
||||||
if (C < ((u32)A << 16)) { // `(C_high < A)` in spec
|
|
||||||
if ((A & 0x8000) == 0) {
|
|
||||||
D = MPS_EXCHANGE();
|
|
||||||
RENORMD();
|
|
||||||
} else {
|
|
||||||
D = MPS(CX);
|
|
||||||
}
|
|
||||||
} else {
|
|
||||||
C = C - ((u32)A << 16); // `C_high = C_high - A` in spec
|
|
||||||
D = LPS_EXCHANGE();
|
|
||||||
RENORMD();
|
|
||||||
}
|
|
||||||
return D;
|
|
||||||
}
|
|
||||||
|
|
||||||
u8 QMArithmeticDecoder::MPS_EXCHANGE()
|
|
||||||
{
|
|
||||||
// Figure E.16 – Decoder MPS path conditional exchange procedure
|
|
||||||
u8 D;
|
|
||||||
if (A < Qe(I(CX))) {
|
|
||||||
D = 1 - MPS(CX);
|
|
||||||
if (SWITCH(I(CX)) == 1) {
|
|
||||||
MPS(CX) = 1 - MPS(CX);
|
|
||||||
}
|
|
||||||
I(CX) = NLPS(I(CX));
|
|
||||||
} else {
|
|
||||||
D = MPS(CX);
|
|
||||||
I(CX) = NMPS(I(CX));
|
|
||||||
}
|
|
||||||
return D;
|
|
||||||
}
|
|
||||||
|
|
||||||
u8 QMArithmeticDecoder::LPS_EXCHANGE()
|
|
||||||
{
|
|
||||||
// Figure E.17 – Decoder LPS path conditional exchange procedure
|
|
||||||
u8 D;
|
|
||||||
if (A < Qe(I(CX))) {
|
|
||||||
A = Qe(I(CX));
|
|
||||||
D = MPS(CX);
|
|
||||||
I(CX) = NMPS(I(CX));
|
|
||||||
} else {
|
|
||||||
A = Qe(I(CX));
|
|
||||||
D = 1 - MPS(CX);
|
|
||||||
if (SWITCH(I(CX)) == 1) {
|
|
||||||
MPS(CX) = 1 - MPS(CX);
|
|
||||||
}
|
|
||||||
I(CX) = NLPS(I(CX));
|
|
||||||
}
|
|
||||||
return D;
|
|
||||||
}
|
|
||||||
|
|
||||||
void QMArithmeticDecoder::RENORMD()
|
|
||||||
{
|
|
||||||
// E.3.3 Renormalization in the decoder (RENORMD)
|
|
||||||
// Figure E.18 – Decoder renormalization procedure
|
|
||||||
do {
|
|
||||||
if (CT == 0)
|
|
||||||
BYTEIN();
|
|
||||||
A = A << 1;
|
|
||||||
C = C << 1;
|
|
||||||
CT = CT - 1;
|
|
||||||
} while ((A & 0x8000) == 0);
|
|
||||||
}
|
|
||||||
|
|
||||||
void QMArithmeticDecoder::BYTEIN()
|
|
||||||
{
|
|
||||||
// E.3.4 Compressed data input (BYTEIN)
|
|
||||||
// Figure G.3 – Inserting a new byte into the C register in the software-conventions decoder
|
|
||||||
if (B() == 0xFF) {
|
|
||||||
if (B(1) > 0x8F) {
|
|
||||||
CT = 8;
|
|
||||||
} else {
|
|
||||||
BP = BP + 1;
|
|
||||||
C = C + 0xFE00 - (B() << 9);
|
|
||||||
CT = 7;
|
|
||||||
}
|
|
||||||
} else {
|
|
||||||
BP = BP + 1;
|
|
||||||
C = C + 0xFF00 - (B() << 8);
|
|
||||||
CT = 8;
|
|
||||||
}
|
|
||||||
}
|
|
||||||
|
|
||||||
namespace JBIG2 {
|
namespace JBIG2 {
|
||||||
|
|
||||||
// Annex A, Arithmetic integer decoding procedure
|
// Annex A, Arithmetic integer decoding procedure
|
||||||
|
|
|
||||||
|
|
@ -14,62 +14,6 @@ namespace Gfx {
|
||||||
|
|
||||||
struct JBIG2LoadingContext;
|
struct JBIG2LoadingContext;
|
||||||
|
|
||||||
// E.3 Arithmetic decoding procedure, but with the changes described in
|
|
||||||
// Annex G Arithmetic decoding procedure (software conventions).
|
|
||||||
// Exposed for testing.
|
|
||||||
class QMArithmeticDecoder {
|
|
||||||
public:
|
|
||||||
struct Context {
|
|
||||||
u8 I { 0 }; // Index I stored for context CX (E.2.4)
|
|
||||||
u8 is_mps { 0 }; // "More probable symbol" (E.1.1). 0 or 1.
|
|
||||||
};
|
|
||||||
|
|
||||||
static ErrorOr<QMArithmeticDecoder> initialize(ReadonlyBytes data);
|
|
||||||
|
|
||||||
bool get_next_bit(Context& context);
|
|
||||||
|
|
||||||
private:
|
|
||||||
QMArithmeticDecoder(ReadonlyBytes data)
|
|
||||||
: m_data(data)
|
|
||||||
{
|
|
||||||
}
|
|
||||||
|
|
||||||
ReadonlyBytes m_data;
|
|
||||||
|
|
||||||
// The code below uses names from the spec, so that the algorithms look exactly like the flowcharts in the spec.
|
|
||||||
|
|
||||||
// Abbreviations:
|
|
||||||
// "CX": "Context" (E.1)
|
|
||||||
// "D": "Decision" (as in "encoder input" / "decoder output") (E.1)
|
|
||||||
// "I(CX)": "Index I stored for context CX" (E.2.4)
|
|
||||||
// "MPS": "More probable symbol" (E.1.1)
|
|
||||||
// "LPS": "Less probable symbol" (E.1.1)
|
|
||||||
|
|
||||||
void INITDEC();
|
|
||||||
u8 DECODE(); // Returns a single decoded bit.
|
|
||||||
u8 MPS_EXCHANGE();
|
|
||||||
u8 LPS_EXCHANGE();
|
|
||||||
void RENORMD();
|
|
||||||
void BYTEIN();
|
|
||||||
|
|
||||||
u8 B(size_t offset = 0) const; // Byte pointed to by BP.
|
|
||||||
size_t BP { 0 }; // Pointer into compressed data.
|
|
||||||
|
|
||||||
// E.3.1 Decoder code register conventions
|
|
||||||
u32 C { 0 }; // Consists of u16 C_high, C_low.
|
|
||||||
u16 A { 0 }; // Current value of the fraction. Fixed precision; 0x8000 is equivalent to 0.75.
|
|
||||||
|
|
||||||
u8 CT { 0 }; // Count of the number of bits in C.
|
|
||||||
|
|
||||||
Context* CX { nullptr };
|
|
||||||
static u8& I(Context* cx) { return cx->I; }
|
|
||||||
static u8& MPS(Context* cx) { return cx->is_mps; }
|
|
||||||
static u16 Qe(u16);
|
|
||||||
static u8 NMPS(u16);
|
|
||||||
static u8 NLPS(u16);
|
|
||||||
static u8 SWITCH(u16);
|
|
||||||
};
|
|
||||||
|
|
||||||
class JBIG2ImageDecoderPlugin : public ImageDecoderPlugin {
|
class JBIG2ImageDecoderPlugin : public ImageDecoderPlugin {
|
||||||
public:
|
public:
|
||||||
static bool sniff(ReadonlyBytes);
|
static bool sniff(ReadonlyBytes);
|
||||||
|
|
|
||||||
209
Userland/Libraries/LibGfx/ImageFormats/QMArithmeticDecoder.cpp
Normal file
209
Userland/Libraries/LibGfx/ImageFormats/QMArithmeticDecoder.cpp
Normal file
|
|
@ -0,0 +1,209 @@
|
||||||
|
/*
|
||||||
|
* Copyright (c) 2024, Nico Weber <thakis@chromium.org>
|
||||||
|
*
|
||||||
|
* SPDX-License-Identifier: BSD-2-Clause
|
||||||
|
*/
|
||||||
|
|
||||||
|
#include <AK/Error.h>
|
||||||
|
#include <LibGfx/ImageFormats/QMArithmeticDecoder.h>
|
||||||
|
|
||||||
|
namespace Gfx {
|
||||||
|
|
||||||
|
// Table E.1 – Qe values and probability estimation process
|
||||||
|
// See also E.1.2 Coding conventions and approximations
|
||||||
|
// and E.2.5 Probability estimation.
|
||||||
|
struct QeEntry {
|
||||||
|
u16 qe; // Sub-interval for the less probable symbol.
|
||||||
|
u16 nmps; // Next index if the more probable symbol is decoded
|
||||||
|
u16 nlps; // Next index if the less probable symbol is decoded
|
||||||
|
u16 switch_flag; // See second-to-last paragraph in E.1.2.
|
||||||
|
};
|
||||||
|
constexpr auto qe_table = to_array<QeEntry>({
|
||||||
|
{ 0x5601, 1, 1, 1 },
|
||||||
|
{ 0x3401, 2, 6, 0 },
|
||||||
|
{ 0x1801, 3, 9, 0 },
|
||||||
|
{ 0x0AC1, 4, 12, 0 },
|
||||||
|
{ 0x0521, 5, 29, 0 },
|
||||||
|
{ 0x0221, 38, 33, 0 },
|
||||||
|
{ 0x5601, 7, 6, 1 },
|
||||||
|
{ 0x5401, 8, 14, 0 },
|
||||||
|
{ 0x4801, 9, 14, 0 },
|
||||||
|
{ 0x3801, 10, 14, 0 },
|
||||||
|
{ 0x3001, 11, 17, 0 },
|
||||||
|
{ 0x2401, 12, 18, 0 },
|
||||||
|
{ 0x1C01, 13, 20, 0 },
|
||||||
|
{ 0x1601, 29, 21, 0 },
|
||||||
|
{ 0x5601, 15, 14, 1 },
|
||||||
|
{ 0x5401, 16, 14, 0 },
|
||||||
|
{ 0x5101, 17, 15, 0 },
|
||||||
|
{ 0x4801, 18, 16, 0 },
|
||||||
|
{ 0x3801, 19, 17, 0 },
|
||||||
|
{ 0x3401, 20, 18, 0 },
|
||||||
|
{ 0x3001, 21, 19, 0 },
|
||||||
|
{ 0x2801, 22, 19, 0 },
|
||||||
|
{ 0x2401, 23, 20, 0 },
|
||||||
|
{ 0x2201, 24, 21, 0 },
|
||||||
|
{ 0x1C01, 25, 22, 0 },
|
||||||
|
{ 0x1801, 26, 23, 0 },
|
||||||
|
{ 0x1601, 27, 24, 0 },
|
||||||
|
{ 0x1401, 28, 25, 0 },
|
||||||
|
{ 0x1201, 29, 26, 0 },
|
||||||
|
{ 0x1101, 30, 27, 0 },
|
||||||
|
{ 0x0AC1, 31, 28, 0 },
|
||||||
|
{ 0x09C1, 32, 29, 0 },
|
||||||
|
{ 0x08A1, 33, 30, 0 },
|
||||||
|
{ 0x0521, 34, 31, 0 },
|
||||||
|
{ 0x0441, 35, 32, 0 },
|
||||||
|
{ 0x02A1, 36, 33, 0 },
|
||||||
|
{ 0x0221, 37, 34, 0 },
|
||||||
|
{ 0x0141, 38, 35, 0 },
|
||||||
|
{ 0x0111, 39, 36, 0 },
|
||||||
|
{ 0x0085, 40, 37, 0 },
|
||||||
|
{ 0x0049, 41, 38, 0 },
|
||||||
|
{ 0x0025, 42, 39, 0 },
|
||||||
|
{ 0x0015, 43, 40, 0 },
|
||||||
|
{ 0x0009, 44, 41, 0 },
|
||||||
|
{ 0x0005, 45, 42, 0 },
|
||||||
|
{ 0x0001, 45, 43, 0 },
|
||||||
|
{ 0x5601, 46, 46, 0 },
|
||||||
|
});
|
||||||
|
|
||||||
|
ErrorOr<QMArithmeticDecoder> QMArithmeticDecoder::initialize(ReadonlyBytes data)
|
||||||
|
{
|
||||||
|
QMArithmeticDecoder decoder { data };
|
||||||
|
decoder.INITDEC();
|
||||||
|
return decoder;
|
||||||
|
}
|
||||||
|
|
||||||
|
bool QMArithmeticDecoder::get_next_bit(Context& context)
|
||||||
|
{
|
||||||
|
CX = &context;
|
||||||
|
// Useful for comparing to Table H.1 – Encoder and decoder trace data.
|
||||||
|
// dbg("I={} MPS={} A={:#x} C={:#x} CT={} B={:#x}", I(CX), MPS(CX), A, C, CT, B());
|
||||||
|
u8 D = DECODE();
|
||||||
|
// dbgln(" -> D={}", D);
|
||||||
|
return D;
|
||||||
|
}
|
||||||
|
|
||||||
|
u16 QMArithmeticDecoder::Qe(u16 index) { return qe_table[index].qe; }
|
||||||
|
u8 QMArithmeticDecoder::NMPS(u16 index) { return qe_table[index].nmps; }
|
||||||
|
u8 QMArithmeticDecoder::NLPS(u16 index) { return qe_table[index].nlps; }
|
||||||
|
u8 QMArithmeticDecoder::SWITCH(u16 index) { return qe_table[index].switch_flag; }
|
||||||
|
|
||||||
|
u8 QMArithmeticDecoder::B(size_t offset) const
|
||||||
|
{
|
||||||
|
// E.2.10 Minimization of the compressed data
|
||||||
|
// "the convention is used in the decoder that when a marker code is encountered,
|
||||||
|
// 1-bits (without bit stuffing) are supplied to the decoder until the coding interval is complete."
|
||||||
|
if (BP + offset >= m_data.size())
|
||||||
|
return 0xFF;
|
||||||
|
return m_data[BP + offset];
|
||||||
|
}
|
||||||
|
|
||||||
|
void QMArithmeticDecoder::INITDEC()
|
||||||
|
{
|
||||||
|
// E.3.5 Initialization of the decoder (INITDEC)
|
||||||
|
// Figure G.1 – Initialization of the software conventions decoder
|
||||||
|
|
||||||
|
// "BP, the pointer to the compressed data, is initialized to BPST (pointing to the first compressed byte)."
|
||||||
|
auto const BPST = 0;
|
||||||
|
BP = BPST;
|
||||||
|
C = (B() ^ 0xFF) << 16;
|
||||||
|
|
||||||
|
BYTEIN();
|
||||||
|
|
||||||
|
C = C << 7;
|
||||||
|
CT = CT - 7;
|
||||||
|
A = 0x8000;
|
||||||
|
}
|
||||||
|
|
||||||
|
u8 QMArithmeticDecoder::DECODE()
|
||||||
|
{
|
||||||
|
// E.3.2 Decoding a decision (DECODE)
|
||||||
|
// Figure G.2 – Decoding an MPS or an LPS in the software-conventions decoder
|
||||||
|
u8 D;
|
||||||
|
A = A - Qe(I(CX));
|
||||||
|
if (C < ((u32)A << 16)) { // `(C_high < A)` in spec
|
||||||
|
if ((A & 0x8000) == 0) {
|
||||||
|
D = MPS_EXCHANGE();
|
||||||
|
RENORMD();
|
||||||
|
} else {
|
||||||
|
D = MPS(CX);
|
||||||
|
}
|
||||||
|
} else {
|
||||||
|
C = C - ((u32)A << 16); // `C_high = C_high - A` in spec
|
||||||
|
D = LPS_EXCHANGE();
|
||||||
|
RENORMD();
|
||||||
|
}
|
||||||
|
return D;
|
||||||
|
}
|
||||||
|
|
||||||
|
u8 QMArithmeticDecoder::MPS_EXCHANGE()
|
||||||
|
{
|
||||||
|
// Figure E.16 – Decoder MPS path conditional exchange procedure
|
||||||
|
u8 D;
|
||||||
|
if (A < Qe(I(CX))) {
|
||||||
|
D = 1 - MPS(CX);
|
||||||
|
if (SWITCH(I(CX)) == 1) {
|
||||||
|
MPS(CX) = 1 - MPS(CX);
|
||||||
|
}
|
||||||
|
I(CX) = NLPS(I(CX));
|
||||||
|
} else {
|
||||||
|
D = MPS(CX);
|
||||||
|
I(CX) = NMPS(I(CX));
|
||||||
|
}
|
||||||
|
return D;
|
||||||
|
}
|
||||||
|
|
||||||
|
u8 QMArithmeticDecoder::LPS_EXCHANGE()
|
||||||
|
{
|
||||||
|
// Figure E.17 – Decoder LPS path conditional exchange procedure
|
||||||
|
u8 D;
|
||||||
|
if (A < Qe(I(CX))) {
|
||||||
|
A = Qe(I(CX));
|
||||||
|
D = MPS(CX);
|
||||||
|
I(CX) = NMPS(I(CX));
|
||||||
|
} else {
|
||||||
|
A = Qe(I(CX));
|
||||||
|
D = 1 - MPS(CX);
|
||||||
|
if (SWITCH(I(CX)) == 1) {
|
||||||
|
MPS(CX) = 1 - MPS(CX);
|
||||||
|
}
|
||||||
|
I(CX) = NLPS(I(CX));
|
||||||
|
}
|
||||||
|
return D;
|
||||||
|
}
|
||||||
|
|
||||||
|
void QMArithmeticDecoder::RENORMD()
|
||||||
|
{
|
||||||
|
// E.3.3 Renormalization in the decoder (RENORMD)
|
||||||
|
// Figure E.18 – Decoder renormalization procedure
|
||||||
|
do {
|
||||||
|
if (CT == 0)
|
||||||
|
BYTEIN();
|
||||||
|
A = A << 1;
|
||||||
|
C = C << 1;
|
||||||
|
CT = CT - 1;
|
||||||
|
} while ((A & 0x8000) == 0);
|
||||||
|
}
|
||||||
|
|
||||||
|
void QMArithmeticDecoder::BYTEIN()
|
||||||
|
{
|
||||||
|
// E.3.4 Compressed data input (BYTEIN)
|
||||||
|
// Figure G.3 – Inserting a new byte into the C register in the software-conventions decoder
|
||||||
|
if (B() == 0xFF) {
|
||||||
|
if (B(1) > 0x8F) {
|
||||||
|
CT = 8;
|
||||||
|
} else {
|
||||||
|
BP = BP + 1;
|
||||||
|
C = C + 0xFE00 - (B() << 9);
|
||||||
|
CT = 7;
|
||||||
|
}
|
||||||
|
} else {
|
||||||
|
BP = BP + 1;
|
||||||
|
C = C + 0xFF00 - (B() << 8);
|
||||||
|
CT = 8;
|
||||||
|
}
|
||||||
|
}
|
||||||
|
|
||||||
|
}
|
||||||
69
Userland/Libraries/LibGfx/ImageFormats/QMArithmeticDecoder.h
Normal file
69
Userland/Libraries/LibGfx/ImageFormats/QMArithmeticDecoder.h
Normal file
|
|
@ -0,0 +1,69 @@
|
||||||
|
/*
|
||||||
|
* Copyright (c) 2024, Nico Weber <thakis@chromium.org>
|
||||||
|
*
|
||||||
|
* SPDX-License-Identifier: BSD-2-Clause
|
||||||
|
*/
|
||||||
|
|
||||||
|
#pragma once
|
||||||
|
|
||||||
|
#include <AK/Span.h>
|
||||||
|
|
||||||
|
namespace Gfx {
|
||||||
|
|
||||||
|
// E.3 Arithmetic decoding procedure, but with the changes described in
|
||||||
|
// Annex G Arithmetic decoding procedure (software conventions).
|
||||||
|
// Exposed for testing.
|
||||||
|
class QMArithmeticDecoder {
|
||||||
|
public:
|
||||||
|
struct Context {
|
||||||
|
u8 I { 0 }; // Index I stored for context CX (E.2.4)
|
||||||
|
u8 is_mps { 0 }; // "More probable symbol" (E.1.1). 0 or 1.
|
||||||
|
};
|
||||||
|
|
||||||
|
static ErrorOr<QMArithmeticDecoder> initialize(ReadonlyBytes data);
|
||||||
|
|
||||||
|
bool get_next_bit(Context& context);
|
||||||
|
|
||||||
|
private:
|
||||||
|
QMArithmeticDecoder(ReadonlyBytes data)
|
||||||
|
: m_data(data)
|
||||||
|
{
|
||||||
|
}
|
||||||
|
|
||||||
|
ReadonlyBytes m_data;
|
||||||
|
|
||||||
|
// The code below uses names from the spec, so that the algorithms look exactly like the flowcharts in the spec.
|
||||||
|
|
||||||
|
// Abbreviations:
|
||||||
|
// "CX": "Context" (E.1)
|
||||||
|
// "D": "Decision" (as in "encoder input" / "decoder output") (E.1)
|
||||||
|
// "I(CX)": "Index I stored for context CX" (E.2.4)
|
||||||
|
// "MPS": "More probable symbol" (E.1.1)
|
||||||
|
// "LPS": "Less probable symbol" (E.1.1)
|
||||||
|
|
||||||
|
void INITDEC();
|
||||||
|
u8 DECODE(); // Returns a single decoded bit.
|
||||||
|
u8 MPS_EXCHANGE();
|
||||||
|
u8 LPS_EXCHANGE();
|
||||||
|
void RENORMD();
|
||||||
|
void BYTEIN();
|
||||||
|
|
||||||
|
u8 B(size_t offset = 0) const; // Byte pointed to by BP.
|
||||||
|
size_t BP { 0 }; // Pointer into compressed data.
|
||||||
|
|
||||||
|
// E.3.1 Decoder code register conventions
|
||||||
|
u32 C { 0 }; // Consists of u16 C_high, C_low.
|
||||||
|
u16 A { 0 }; // Current value of the fraction. Fixed precision; 0x8000 is equivalent to 0.75.
|
||||||
|
|
||||||
|
u8 CT { 0 }; // Count of the number of bits in C.
|
||||||
|
|
||||||
|
Context* CX { nullptr };
|
||||||
|
static u8& I(Context* cx) { return cx->I; }
|
||||||
|
static u8& MPS(Context* cx) { return cx->is_mps; }
|
||||||
|
static u16 Qe(u16);
|
||||||
|
static u8 NMPS(u16);
|
||||||
|
static u8 NLPS(u16);
|
||||||
|
static u8 SWITCH(u16);
|
||||||
|
};
|
||||||
|
|
||||||
|
}
|
||||||
Loading…
Add table
Add a link
Reference in a new issue