[Pkg-javascript-commits] [pdf.js] 206/246: Reduce ASCII checks in makeInlineImage().

[David Prévot]

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taffit pushed a commit to branch master
in repository pdf.js.

commit ffae848f4ea24c58f45ed14102a2670627f49ca4
Author: Nicholas Nethercote <nnethercote at mozilla.com>
Date:   Wed Aug 13 23:25:45 2014 -0700

    Reduce ASCII checks in makeInlineImage().
    
    makeInlineImage() has a "are the next five chars ASCII?" check which is
    run after an "EI" sequence has been found. This check involves the
    creation of a new object because peekBytes() calls subarray().
    
    Unfortunately, the check is currently run on whitespace chars even when
    an "EI" sequence has not yet been found, i.e. when it's not needed. For
    the PDF in #2618, there are over 820,000 such checks.
    
    This change reworks the relevant loop so that the check is only done
    once an "EI" sequence has been seen. This reduces the number of checks
    to 157,000, and speeds up rendering by somewhere between 2% and 7% (the
    measurements are noisy).
---
 src/core/parser.js | 45 +++++++++++++++++++++++----------------------
 1 file changed, 23 insertions(+), 22 deletions(-)

diff --git a/src/core/parser.js b/src/core/parser.js
index ec0666a..1f78d22 100644
--- a/src/core/parser.js
+++ b/src/core/parser.js
@@ -18,7 +18,7 @@
            FlateStream, isArray, isCmd, isDict, isInt, isName, isNum, isRef,
            isString, Jbig2Stream, JpegStream, JpxStream, LZWStream, Name,
            NullStream, PredictorStream, Ref, RunLengthStream, warn, info,
-           StreamType, MissingDataException */
+           StreamType, MissingDataException, assert */
 
 'use strict';
 
@@ -152,32 +152,33 @@ var Parser = (function ParserClosure() {
 
       // searching for the /EI\s/
       var state = 0, ch, i, ii;
-      while (state !== 4 && (ch = stream.getByte()) !== -1) {
-        switch (ch | 0) {
-          case 0x20:
-          case 0x0D:
-          case 0x0A:
-            // let's check next five bytes to be ASCII... just be sure
-            var followingBytes = stream.peekBytes(5);
-            for (i = 0, ii = followingBytes.length; i < ii; i++) {
+      var E = 0x45, I = 0x49, SPACE = 0x20, NL = 0xA, CR = 0xD;
+      while ((ch = stream.getByte()) !== -1) {
+        if (state === 0) {
+          state = (ch === E) ? 1 : 0;
+        } else if (state === 1) {
+          state = (ch === I) ? 2 : 0;
+        } else {
+          assert(state === 2);
+          if (ch === SPACE || ch === NL || ch === CR) {
+            // Let's check the next five bytes are ASCII... just be sure.
+            var n = 5;
+            var followingBytes = stream.peekBytes(n);
+            for (i = 0; i < n; i++) {
               ch = followingBytes[i];
-              if (ch !== 0x0A && ch !== 0x0D && (ch < 0x20 || ch > 0x7F)) {
-                // not a LF, CR, SPACE or any visible ASCII character
+              if (ch !== NL && ch !== CR && (ch < SPACE || ch > 0x7F)) {
+                // Not a LF, CR, SPACE or any visible ASCII character, i.e.
+                // it's binary stuff. Resetting the state.
                 state = 0;
-                break; // some binary stuff found, resetting the state
+                break;
               }
             }
-            state = (state === 3 ? 4 : 0);
-            break;
-          case 0x45:
-            state = 2;
-            break;
-          case 0x49:
-            state = (state === 2 ? 3 : 0);
-            break;
-          default:
+            if (state === 2) {
+              break;  // finished!
+            }
+          } else {
             state = 0;
-            break;
+          }
         }
       }
 

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