Add different code-paths to `{CMap, ToUnicodeMap}.charCodeOf` depending on length, since `Array.prototype.indexOf` can be extremely inefficient for very large arrays (issue 8372)

Fixes 8372.

src/core/cmap.js

@@ -283,24 +283,34 @@ var CMap = (function CMapClosure() {
       // indices in the *billions*. For such tables we use for..in, which isn't
       // ideal because it stringifies the indices for all present elements, but
       // it does avoid iterating over every undefined entry.
-      var map = this._map;
-      var length = map.length;
-      var i;
+      let map = this._map;
+      let length = map.length;
       if (length <= 0x10000) {
-        for (i = 0; i < length; i++) {
+        for (let i = 0; i < length; i++) {
           if (map[i] !== undefined) {
             callback(i, map[i]);
           }
         }
       } else {
-        for (i in this._map) {
+        for (let i in map) {
           callback(i, map[i]);
         }
       }
     },
 
     charCodeOf(value) {
-      return this._map.indexOf(value);
+      // `Array.prototype.indexOf` is *extremely* inefficient for arrays which
+      // are both very sparse and very large (see issue8372.pdf).
+      let map = this._map;
+      if (map.length <= 0x10000) {
+        return map.indexOf(value);
+      }
+      for (let charCode in map) {
+        if (map[charCode] === value) {
+          return (charCode | 0);
+        }
+      }
+      return -1;
     },
 
     getMap() {

src/core/fonts.js

@@ -283,8 +283,19 @@ var ToUnicodeMap = (function ToUnicodeMapClosure() {
       return this._map[i];
     },
 
-    charCodeOf(v) {
-      return this._map.indexOf(v);
+    charCodeOf(value) {
+      // `Array.prototype.indexOf` is *extremely* inefficient for arrays which
+      // are both very sparse and very large (see issue8372.pdf).
+      let map = this._map;
+      if (map.length <= 0x10000) {
+        return map.indexOf(value);
+      }
+      for (let charCode in map) {
+        if (map[charCode] === value) {
+          return (charCode | 0);
+        }
+      }
+      return -1;
     },
 
     amend(map) {

test/pdfs/.gitignore

@@ -50,6 +50,7 @@
 !issue8061.pdf
 !issue8088.pdf
 !issue8125.pdf
+!issue8372.pdf
 !issue8424.pdf
 !bad-PageLabels.pdf
 !filled-background.pdf

test/pdfs/issue8372.pdf

@@ -0,0 +1,101 @@
+%PDF-1.7
+%âãÏÓ
+1 0 obj 
+<<
+/BaseFont /AdobeHeitiStd-Regular
+/CIDSystemInfo 2 0 R
+/Subtype /CIDFontType2
+/FontDescriptor 3 0 R
+/Type /Font
+>>
+endobj 
+3 0 obj 
+<<
+/FontName /AdobeHeitiStd-Regular
+/StemV 56
+/Ascent 967
+/Flags 32
+/Descent -283
+/ItalicAngle 0
+/FontBBox [-163 -283 1087 967]
+/Type /FontDescriptor
+/CapHeight 763
+>>
+endobj 
+2 0 obj 
+<<
+/Supplement 4
+/Ordering (GB1)
+/Registry (Adobe)
+>>
+endobj 
+4 0 obj 
+<<
+/Pages 5 0 R
+/Type /Catalog
+>>
+endobj 
+5 0 obj 
+<<
+/MediaBox [0 0 200 50]
+/Kids [6 0 R]
+/Count 1
+/Type /Pages
+>>
+endobj 
+6 0 obj 
+<<
+/Parent 5 0 R
+/MediaBox [0 0 200 50]
+/Resources 
+<<
+/Font 
+<<
+/F1 7 0 R
+>>
+>>
+/Contents 8 0 R
+/Type /Page
+>>
+endobj 
+7 0 obj 
+<<
+/DescendantFonts [1 0 R]
+/BaseFont /AdobeHeitiStd-Regular
+/Subtype /Type0
+/Encoding /UniGB-UTF16-H
+/Type /Font
+>>
+endobj 
+8 0 obj 
+<<
+/Length 46
+>>
+stream
+BT
+10 20 TD
+/F1 20 Tf
+[(vî)0.389893(_U)]TJ
+ET
+
+endstream 
+endobj xref
+0 9
+0000000000 65535 f 
+0000000015 00000 n 
+0000000334 00000 n 
+0000000149 00000 n 
+0000000405 00000 n 
+0000000456 00000 n 
+0000000538 00000 n 
+0000000667 00000 n 
+0000000801 00000 n 
+trailer
+
+<<
+/Root 4 0 R
+/Size 9
+>>
+startxref
+899
+%%EOF

test/test_manifest.json

@@ -2125,6 +2125,13 @@
        "link": false,
        "type": "text"
     },
+    {  "id": "issue8372-text",
+       "file": "pdfs/issue8372.pdf",
+       "md5": "b02fb07364dd00ad5044bd259860da97",
+       "rounds": 1,
+       "link": false,
+       "type": "text"
+    },
     {  "id": "bug894572",
        "file": "pdfs/bug894572.pdf",
        "md5": "e54a6b0451939f685ed37e3d46e16158",