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Merge pull request #3542 from fkaelberer/FasterJBIG2decode

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Faster JBIG2 decoding for Firefox
This commit is contained in:
Yury Delendik 2013-08-06 13:08:19 -07:00
commit 6736cca8c4
1 changed files with 44 additions and 69 deletions
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113
src/jbig2.js Normal file → Executable file
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@ -114,26 +114,50 @@ var Jbig2Image = (function Jbig2ImageClosure() {
this.clow &= 0xFFFF;
}
},
readBit: function ArithmeticDecoder_readBit(cx) {
var qeIcx = QeTable[cx.index].qe;
readBit: function ArithmeticDecoder_readBit(contexts, pos) {
// contexts are packed into 1 byte:
// highest 7 bits carry cx.index, lowest bit carries cx.mps
var cx_index = contexts[pos] >> 1, cx_mps = contexts[pos] & 1;
var qeTableIcx = QeTable[cx_index];
var qeIcx = qeTableIcx.qe;
var nmpsIcx = qeTableIcx.nmps;
var nlpsIcx = qeTableIcx.nlps;
var switchIcx = qeTableIcx.switchFlag;
var d;
this.a -= qeIcx;
if (this.chigh < qeIcx) {
var d = this.exchangeLps(cx);
this.renormD();
return d;
// exchangeLps
if (this.a < qeIcx) {
this.a = qeIcx;
d = cx_mps;
cx_index = nmpsIcx;
} else {
this.a = qeIcx;
d = 1 - cx_mps;
if (switchIcx) {
cx_mps = d;
}
cx_index = nlpsIcx;
}
} else {
this.chigh -= qeIcx;
if ((this.a & 0x8000) === 0) {
var d = this.exchangeMps(cx);
this.renormD();
return d;
if ((this.a & 0x8000) !== 0) {
return cx_mps;
}
// exchangeMps
if (this.a < qeIcx) {
d = 1 - cx_mps;
if (switchIcx) {
cx_mps = d;
}
cx_index = nlpsIcx;
} else {
return cx.mps;
d = cx_mps;
cx_index = nmpsIcx;
}
}
},
renormD: function ArithmeticDecoder_renormD() {
// renormD;
do {
if (this.ct === 0)
this.byteIn();
@ -143,39 +167,8 @@ var Jbig2Image = (function Jbig2ImageClosure() {
this.clow = (this.clow << 1) & 0xFFFF;
this.ct--;
} while ((this.a & 0x8000) === 0);
},
exchangeMps: function ArithmeticDecoder_exchangeMps(cx) {
var d;
var qeTableIcx = QeTable[cx.index];
if (this.a < qeTableIcx.qe) {
d = 1 - cx.mps;
if (qeTableIcx.switchFlag == 1) {
cx.mps = 1 - cx.mps;
}
cx.index = qeTableIcx.nlps;
} else {
d = cx.mps;
cx.index = qeTableIcx.nmps;
}
return d;
},
exchangeLps: function ArithmeticDecoder_exchangeLps(cx) {
var d;
var qeTableIcx = QeTable[cx.index];
if (this.a < qeTableIcx.qe) {
this.a = qeTableIcx.qe;
d = cx.mps;
cx.index = qeTableIcx.nmps;
} else {
this.a = qeTableIcx.qe;
d = 1 - cx.mps;
if (qeTableIcx.switchFlag == 1) {
cx.mps = 1 - cx.mps;
}
cx.index = qeTableIcx.nlps;
}
contexts[pos] = cx_index << 1 | cx_mps;
return d;
}
};
@ -190,7 +183,7 @@ var Jbig2Image = (function Jbig2ImageClosure() {
getContexts: function(id) {
if (id in this)
return this[id];
return (this[id] = []);
return (this[id] = new Int8Array(1<<16));
}
};
@ -220,10 +213,7 @@ var Jbig2Image = (function Jbig2ImageClosure() {
var state = 1, v = 0, s;
var toRead = 32, offset = 4436; // defaults for state 7
while (state) {
var cx = contexts[prev];
if (!cx)
contexts[prev] = cx = {index: 0, mps: 0};
var bit = decoder.readBit(cx);
var bit = decoder.readBit(contexts, prev);
prev = prev < 256 ? (prev << 1) | bit :
(((prev << 1) | bit) & 511) | 256;
switch (state) {
@ -278,10 +268,7 @@ var Jbig2Image = (function Jbig2ImageClosure() {
var prev = 1;
for (var i = 0; i < codeLength; i++) {
var cx = contexts[prev];
if (!cx)
contexts[prev] = cx = {index: 0, mps: 0};
var bit = decoder.readBit(cx);
var bit = decoder.readBit(contexts, prev);
prev = (prev * 2) + bit;
}
if (codeLength < 31)
@ -398,10 +385,7 @@ var Jbig2Image = (function Jbig2ImageClosure() {
var ltp = 0;
for (var i = 0; i < height; i++) {
if (prediction) {
var cx = contexts[pseudoPixelContext];
if (!cx)
contexts[pseudoPixelContext] = cx = {index: 0, mps: 0};
var sltp = decoder.readBit(cx);
var sltp = decoder.readBit(contexts, pseudoPixelContext);
ltp ^= sltp;
}
if (ltp) {
@ -423,10 +407,7 @@ var Jbig2Image = (function Jbig2ImageClosure() {
else
contextLabel = (contextLabel << 1) | bitmap[i0][j0];
}
var cx = contexts[contextLabel];
if (!cx)
contexts[contextLabel] = cx = {index: 0, mps: 0};
var pixel = decoder.readBit(cx);
var pixel = decoder.readBit(contexts, contextLabel);
row[j] = pixel;
}
}
@ -469,10 +450,7 @@ var Jbig2Image = (function Jbig2ImageClosure() {
var ltp = 0;
for (var i = 0; i < height; i++) {
if (prediction) {
var cx = contexts[pseudoPixelContext];
if (!cx)
contexts[pseudoPixelContext] = cx = {index: 0, mps: 0};
var sltp = decoder.readBit(cx);
var sltp = decoder.readBit(contexts, pseudoPixelContext);
ltp ^= sltp;
}
var row = new Uint8Array(width);
@ -497,10 +475,7 @@ var Jbig2Image = (function Jbig2ImageClosure() {
else
contextLabel = (contextLabel << 1) | referenceBitmap[i0][j0];
}
var cx = contexts[contextLabel];
if (!cx)
contexts[contextLabel] = cx = {index: 0, mps: 0};
var pixel = decoder.readBit(cx);
var pixel = decoder.readBit(contexts, contextLabel);
row[j] = pixel;
}
}