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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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21
src/core/evaluator.js
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@ -643,7 +643,7 @@ var PartialEvaluator = (function PartialEvaluatorClosure() {
var preprocessor = new EvaluatorPreprocessor(stream, xref);
var res = resources;
var chunk = '';
var chunkBuf = [];
var font = null;
var charSpace = 0, wordSpace = 0;
var operation;
@ -692,37 +692,37 @@ var PartialEvaluator = (function PartialEvaluatorClosure() {
var items = args[0];
for (var j = 0, jj = items.length; j < jj; j++) {
if (typeof items[j] === 'string') {
chunk += fontCharsToUnicode(items[j], font);
chunkBuf.push(fontCharsToUnicode(items[j], font));
} else if (items[j] < 0 && font.spaceWidth > 0) {
var fakeSpaces = -items[j] / font.spaceWidth;
if (fakeSpaces > MULTI_SPACE_FACTOR) {
fakeSpaces = Math.round(fakeSpaces);
while (fakeSpaces--) {
chunk += ' ';
chunkBuf.push(' ');
}
} else if (fakeSpaces > SPACE_FACTOR) {
chunk += ' ';
chunkBuf.push(' ');
}
}
}
break;
case OPS.showText:
chunk += fontCharsToUnicode(args[0], font);
chunkBuf.push(fontCharsToUnicode(args[0], font));
break;
case OPS.nextLineShowText:
// For search, adding a extra white space for line breaks would be
// better here, but that causes too much spaces in the
// text-selection divs.
chunk += fontCharsToUnicode(args[0], font);
chunkBuf.push(fontCharsToUnicode(args[0], font));
break;
case OPS.nextLineSetSpacingShowText:
// Note comment in "'"
chunk += fontCharsToUnicode(args[2], font);
chunkBuf.push(fontCharsToUnicode(args[2], font));
break;
case OPS.paintXObject:
// Set the chunk such that the following if won't add something
// to the state.
chunk = '';
chunkBuf.length = 0;
if (args[0].code) {
break;
@ -771,7 +771,8 @@ var PartialEvaluator = (function PartialEvaluatorClosure() {
break;
} // switch
if (chunk !== '') {
if (chunkBuf.length > 0) {
var chunk = chunkBuf.join('');
var bidiResult = PDFJS.bidi(chunk, -1, font.vertical);
var bidiText = {
str: bidiResult.str,
@ -793,7 +794,7 @@ var PartialEvaluator = (function PartialEvaluatorClosure() {
bidiText.size = fontHeight;
bidiTexts.push(bidiText);
chunk = '';
chunkBuf.length = 0;
}
} // while