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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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82
src/core/stream.js
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@ -98,11 +98,18 @@ var StringStream = (function StringStreamClosure() {
// super class for the decoding streams
var DecodeStream = (function DecodeStreamClosure() {
function DecodeStream() {
function DecodeStream(maybeMinBufferLength) {
this.pos = 0;
this.bufferLength = 0;
this.eof = false;
this.buffer = null;
this.minBufferLength = 512;
if (maybeMinBufferLength) {
// Compute the first power of two that is as big as maybeMinBufferLength.
while (this.minBufferLength < maybeMinBufferLength) {
this.minBufferLength *= 2;
}
}
}
DecodeStream.prototype = {
@ -117,7 +124,7 @@ var DecodeStream = (function DecodeStreamClosure() {
} else {
current = 0;
}
var size = 512;
var size = this.minBufferLength;
while (size < requested) {
size *= 2;
}
@ -197,7 +204,7 @@ var DecodeStream = (function DecodeStreamClosure() {
var StreamsSequenceStream = (function StreamsSequenceStreamClosure() {
function StreamsSequenceStream(streams) {
this.streams = streams;
DecodeStream.call(this);
DecodeStream.call(this, /* maybeLength = */ null);
}
StreamsSequenceStream.prototype = Object.create(DecodeStream.prototype);
@ -328,7 +335,7 @@ var FlateStream = (function FlateStreamClosure() {
0x50003, 0x50013, 0x5000b, 0x5001b, 0x50007, 0x50017, 0x5000f, 0x00000
]), 5];
function FlateStream(str) {
function FlateStream(str, maybeLength) {
this.str = str;
this.dict = str.dict;
@ -346,7 +353,7 @@ var FlateStream = (function FlateStreamClosure() {
this.codeSize = 0;
this.codeBuf = 0;
DecodeStream.call(this);
DecodeStream.call(this, maybeLength);
}
FlateStream.prototype = Object.create(DecodeStream.prototype);
@ -581,7 +588,7 @@ var FlateStream = (function FlateStreamClosure() {
})();
var PredictorStream = (function PredictorStreamClosure() {
function PredictorStream(str, params) {
function PredictorStream(str, maybeLength, params) {
var predictor = this.predictor = params.get('Predictor') || 1;
if (predictor <= 1)
@ -604,7 +611,7 @@ var PredictorStream = (function PredictorStreamClosure() {
this.pixBytes = (colors * bits + 7) >> 3;
this.rowBytes = (columns * colors * bits + 7) >> 3;
DecodeStream.call(this);
DecodeStream.call(this, maybeLength);
return this;
}
@ -774,21 +781,22 @@ var PredictorStream = (function PredictorStreamClosure() {
* DecodeStreams.
*/
var JpegStream = (function JpegStreamClosure() {
function JpegStream(stream, length, dict, xref) {
function JpegStream(stream, maybeLength, dict, xref) {
// TODO: per poppler, some images may have 'junk' before that
// need to be removed
this.stream = stream;
this.length = length;
this.maybeLength = maybeLength;
this.dict = dict;
DecodeStream.call(this);
DecodeStream.call(this, maybeLength);
}
JpegStream.prototype = Object.create(DecodeStream.prototype);
Object.defineProperty(JpegStream.prototype, 'bytes', {
get: function JpegStream_bytes() {
return shadow(this, 'bytes', this.stream.getBytes(this.length));
// If this.maybeLength is null, we'll get the entire stream.
return shadow(this, 'bytes', this.stream.getBytes(this.maybeLength));
},
configurable: true
});
@ -841,19 +849,20 @@ var JpegStream = (function JpegStreamClosure() {
* the stream behaves like all the other DecodeStreams.
*/
var JpxStream = (function JpxStreamClosure() {
function JpxStream(stream, length, dict) {
function JpxStream(stream, maybeLength, dict) {
this.stream = stream;
this.length = length;
this.maybeLength = maybeLength;
this.dict = dict;
DecodeStream.call(this);
DecodeStream.call(this, maybeLength);
}
JpxStream.prototype = Object.create(DecodeStream.prototype);
Object.defineProperty(JpxStream.prototype, 'bytes', {
get: function JpxStream_bytes() {
return shadow(this, 'bytes', this.stream.getBytes(this.length));
// If this.maybeLength is null, we'll get the entire stream.
return shadow(this, 'bytes', this.stream.getBytes(this.maybeLength));
},
configurable: true
});
@ -948,19 +957,20 @@ var JpxStream = (function JpxStreamClosure() {
* the stream behaves like all the other DecodeStreams.
*/
var Jbig2Stream = (function Jbig2StreamClosure() {
function Jbig2Stream(stream, length, dict) {
function Jbig2Stream(stream, maybeLength, dict) {
this.stream = stream;
this.length = length;
this.maybeLength = maybeLength;
this.dict = dict;
DecodeStream.call(this);
DecodeStream.call(this, maybeLength);
}
Jbig2Stream.prototype = Object.create(DecodeStream.prototype);
Object.defineProperty(Jbig2Stream.prototype, 'bytes', {
get: function Jbig2Stream_bytes() {
return shadow(this, 'bytes', this.stream.getBytes(this.length));
// If this.maybeLength is null, we'll get the entire stream.
return shadow(this, 'bytes', this.stream.getBytes(this.maybeLength));
},
configurable: true
});
@ -1004,14 +1014,14 @@ var Jbig2Stream = (function Jbig2StreamClosure() {
})();
var DecryptStream = (function DecryptStreamClosure() {
function DecryptStream(str, decrypt) {
function DecryptStream(str, maybeLength, decrypt) {
this.str = str;
this.dict = str.dict;
this.decrypt = decrypt;
this.nextChunk = null;
this.initialized = false;
DecodeStream.call(this);
DecodeStream.call(this, maybeLength);
}
var chunkSize = 512;
@ -1048,12 +1058,17 @@ var DecryptStream = (function DecryptStreamClosure() {
})();
var Ascii85Stream = (function Ascii85StreamClosure() {
function Ascii85Stream(str) {
function Ascii85Stream(str, maybeLength) {
this.str = str;
this.dict = str.dict;
this.input = new Uint8Array(5);
DecodeStream.call(this);
// Most streams increase in size when decoded, but Ascii85 streams
// typically shrink by ~20%.
if (maybeLength) {
maybeLength = 0.8 * maybeLength;
}
DecodeStream.call(this, maybeLength);
}
Ascii85Stream.prototype = Object.create(DecodeStream.prototype);
@ -1121,13 +1136,18 @@ var Ascii85Stream = (function Ascii85StreamClosure() {
})();
var AsciiHexStream = (function AsciiHexStreamClosure() {
function AsciiHexStream(str) {
function AsciiHexStream(str, maybeLength) {
this.str = str;
this.dict = str.dict;
this.firstDigit = -1;
DecodeStream.call(this);
// Most streams increase in size when decoded, but AsciiHex streams shrink
// by 50%.
if (maybeLength) {
maybeLength = 0.5 * maybeLength;
}
DecodeStream.call(this, maybeLength);
}
AsciiHexStream.prototype = Object.create(DecodeStream.prototype);
@ -1178,11 +1198,11 @@ var AsciiHexStream = (function AsciiHexStreamClosure() {
})();
var RunLengthStream = (function RunLengthStreamClosure() {
function RunLengthStream(str) {
function RunLengthStream(str, maybeLength) {
this.str = str;
this.dict = str.dict;
DecodeStream.call(this);
DecodeStream.call(this, maybeLength);
}
RunLengthStream.prototype = Object.create(DecodeStream.prototype);
@ -1650,7 +1670,7 @@ var CCITTFaxStream = (function CCITTFaxStreamClosure() {
[2, 2], [2, 2], [2, 2], [2, 2]
];
function CCITTFaxStream(str, params) {
function CCITTFaxStream(str, maybeLength, params) {
this.str = str;
this.dict = str.dict;
@ -1691,7 +1711,7 @@ var CCITTFaxStream = (function CCITTFaxStreamClosure() {
this.eatBits(1);
}
DecodeStream.call(this);
DecodeStream.call(this, maybeLength);
}
CCITTFaxStream.prototype = Object.create(DecodeStream.prototype);
@ -2186,7 +2206,7 @@ var CCITTFaxStream = (function CCITTFaxStreamClosure() {
})();
var LZWStream = (function LZWStreamClosure() {
function LZWStream(str, earlyChange) {
function LZWStream(str, maybeLength, earlyChange) {
this.str = str;
this.dict = str.dict;
this.cachedData = 0;
@ -2209,7 +2229,7 @@ var LZWStream = (function LZWStreamClosure() {
}
this.lzwState = lzwState;
DecodeStream.call(this);
DecodeStream.call(this, maybeLength);
}
LZWStream.prototype = Object.create(DecodeStream.prototype);