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Estimate the size of decoded streams in advance.

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When decoding a stream, the decode buffer is often grown multiple times, its
byte size increasing like so: 512, 1024, 2048, etc. This patch estimates the
minimum size in advance (using the length of the encoded stream), often
allowing the smaller sizes to be skipped. It also renames numerous |length|
variables as |maybeLength| to make it clear that they can be |null|.

I measured this change on eight documents. This change reduces the cumulative
size of decode buffer allocations by 0--32%, with 10--20% being typical. This
reduces peak RSS by 10 or 20 MiB for several of them.
This commit is contained in:
Nicholas Nethercote 2014-03-10 22:18:30 -07:00
parent c3ed71c9c5
commit b3024db677
5 changed files with 85 additions and 60 deletions
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36
src/core/parser.js
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@ -170,7 +170,7 @@ var Parser = (function ParserClosure() {
var length = (stream.pos - 4) - startPos;
var imageStream = stream.makeSubStream(startPos, length, dict);
if (cipherTransform)
imageStream = cipherTransform.createStream(imageStream);
imageStream = cipherTransform.createStream(imageStream, length);
imageStream = this.filter(imageStream, dict, length);
imageStream.dict = dict;
@ -251,7 +251,7 @@ var Parser = (function ParserClosure() {
stream = stream.makeSubStream(pos, length, dict);
if (cipherTransform)
stream = cipherTransform.createStream(stream);
stream = cipherTransform.createStream(stream, length);
stream = this.filter(stream, dict, length);
stream.dict = dict;
return stream;
@ -261,6 +261,8 @@ var Parser = (function ParserClosure() {
var params = this.fetchIfRef(dict.get('DecodeParms', 'DP'));
if (isName(filter))
return this.makeFilter(stream, filter.name, length, params);
var maybeLength = length;
if (isArray(filter)) {
var filterArray = filter;
var paramsArray = params;
@ -272,22 +274,23 @@ var Parser = (function ParserClosure() {
params = null;
if (isArray(paramsArray) && (i in paramsArray))
params = paramsArray[i];
stream = this.makeFilter(stream, filter.name, length, params);
stream = this.makeFilter(stream, filter.name, maybeLength, params);
// after the first stream the length variable is invalid
length = null;
maybeLength = null;
}
}
return stream;
},
makeFilter: function Parser_makeFilter(stream, name, length, params) {
makeFilter: function Parser_makeFilter(stream, name, maybeLength, params) {
if (stream.dict.get('Length') === 0) {
return new NullStream(stream);
}
if (name == 'FlateDecode' || name == 'Fl') {
if (params) {
return new PredictorStream(new FlateStream(stream), params);
return new PredictorStream(new FlateStream(stream, maybeLength),
maybeLength, params);
}
return new FlateStream(stream);
return new FlateStream(stream, maybeLength);
}
if (name == 'LZWDecode' || name == 'LZW') {
var earlyChange = 1;
@ -295,30 +298,31 @@ var Parser = (function ParserClosure() {
if (params.has('EarlyChange'))
earlyChange = params.get('EarlyChange');
return new PredictorStream(
new LZWStream(stream, earlyChange), params);
new LZWStream(stream, maybeLength, earlyChange),
maybeLength, params);
}
return new LZWStream(stream, earlyChange);
return new LZWStream(stream, maybeLength, earlyChange);
}
if (name == 'DCTDecode' || name == 'DCT') {
return new JpegStream(stream, length, stream.dict, this.xref);
return new JpegStream(stream, maybeLength, stream.dict, this.xref);
}
if (name == 'JPXDecode' || name == 'JPX') {
return new JpxStream(stream, length, stream.dict);
return new JpxStream(stream, maybeLength, stream.dict);
}
if (name == 'ASCII85Decode' || name == 'A85') {
return new Ascii85Stream(stream);
return new Ascii85Stream(stream, maybeLength);
}
if (name == 'ASCIIHexDecode' || name == 'AHx') {
return new AsciiHexStream(stream);
return new AsciiHexStream(stream, maybeLength);
}
if (name == 'CCITTFaxDecode' || name == 'CCF') {
return new CCITTFaxStream(stream, params);
return new CCITTFaxStream(stream, maybeLength, params);
}
if (name == 'RunLengthDecode' || name == 'RL') {
return new RunLengthStream(stream);
return new RunLengthStream(stream, maybeLength);
}
if (name == 'JBIG2Decode') {
return new Jbig2Stream(stream, length, stream.dict);
return new Jbig2Stream(stream, maybeLength, stream.dict);
}
warn('filter "' + name + '" not supported yet');
return stream;