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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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2
test/unit/stream_spec.js
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@ -30,7 +30,7 @@ describe('stream', function() {
var input = new Stream(new Uint8Array([2, 100, 3, 2, 1, 255, 2, 1, 255]),
0, 9, dict);
var predictor = new PredictorStream(input, dict);
var predictor = new PredictorStream(input, /* length = */ 9, dict);
var result = predictor.getBytes(6);
expect(result).toMatchTypedArray(