[Pkg-javascript-commits] [pdf.js] 171/207: Improve how DecodeStream handles empty buffers.
David Prévot
taffit at moszumanska.debian.org
Mon Jul 28 15:36:45 UTC 2014
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taffit pushed a commit to branch master
in repository pdf.js.
commit db866945b7650d96c052c184c58856d7df277e5c
Author: Nicholas Nethercote <nnethercote at mozilla.com>
Date: Wed Jul 2 18:39:23 2014 -0700
Improve how DecodeStream handles empty buffers.
DecodeStream currently initializes its |buffer| field to |null|, which
is reasonable, because lots of DecodeStreams never need to instantiate a
buffer. But this requires various special cases in the code.
This patch change it so DecodeStreamClosure has a single empty
Uint8Array which gets shared between all buffers upon initialization.
This avoids the special cases.
DecodeStream.prototype.ensureBuffer() is really hot, and this removes a
test from the fast path. For one 226 page scanned document this sped up
rendering by about 2%.
---
src/core/stream.js | 28 ++++++++++------------------
1 file changed, 10 insertions(+), 18 deletions(-)
diff --git a/src/core/stream.js b/src/core/stream.js
index 406d4d9..e8afcc8 100644
--- a/src/core/stream.js
+++ b/src/core/stream.js
@@ -116,11 +116,17 @@ var StringStream = (function StringStreamClosure() {
// super class for the decoding streams
var DecodeStream = (function DecodeStreamClosure() {
+ // Lots of DecodeStreams are created whose buffers are never used. For these
+ // we share a single empty buffer. This is (a) space-efficient and (b) avoids
+ // having special cases that would be required if we used |null| for an empty
+ // buffer.
+ var emptyBuffer = new Uint8Array(0);
+
function DecodeStream(maybeMinBufferLength) {
this.pos = 0;
this.bufferLength = 0;
this.eof = false;
- this.buffer = null;
+ this.buffer = emptyBuffer;
this.minBufferLength = 512;
if (maybeMinBufferLength) {
// Compute the first power of two that is as big as maybeMinBufferLength.
@@ -139,23 +145,15 @@ var DecodeStream = (function DecodeStreamClosure() {
},
ensureBuffer: function DecodeStream_ensureBuffer(requested) {
var buffer = this.buffer;
- var current;
- if (buffer) {
- current = buffer.byteLength;
- if (requested <= current) {
- return buffer;
- }
- } else {
- current = 0;
+ if (requested <= buffer.byteLength) {
+ return buffer;
}
var size = this.minBufferLength;
while (size < requested) {
size *= 2;
}
var buffer2 = new Uint8Array(size);
- if (buffer) {
- buffer2.set(buffer);
- }
+ buffer2.set(buffer);
return (this.buffer = buffer2);
},
getByte: function DecodeStream_getByte() {
@@ -199,12 +197,6 @@ var DecodeStream = (function DecodeStreamClosure() {
this.readBlock();
}
end = this.bufferLength;
-
- // checking if bufferLength is still 0 then
- // the buffer has to be initialized
- if (!end) {
- this.buffer = new Uint8Array(0);
- }
}
this.pos = end;
--
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