Introduce Math.sumPrecise usage in the code-base

This is a new JavaScript feature that makes it easy to compute the sum of list of values; see https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Math/sumPrecise

This allows us to remove most cases of `Array.prototype.reduce`, which helps improve readability since that (in my opinion) often isn't the most intuitive code.

Author: Snuffleupagus

src/core/annotation.js

@@ -2572,11 +2572,7 @@ class WidgetAnnotation extends Annotation {
   }
 
   _getTextWidth(text, font) {
-    return (
-      font
-        .charsToGlyphs(text)
-        .reduce((width, glyph) => width + glyph.width, 0) / 1000
-    );
+    return Math.sumPrecise(font.charsToGlyphs(text).map(g => g.width)) / 1000;
   }
 
   _computeFontSize(height, width, text, font, lineCount) {

src/core/crypto.js

@@ -720,7 +720,7 @@ class PDF20 extends PDFBase {
       // The number is e0 + 256 * e1 + 256^2 * e2... and 256 % 3 === 1, hence
       // the powers of 256 are === 1 modulo 3 and finally the number modulo 3
       // is equal to the remainder modulo 3 of the sum of the e_n.
-      const remainder = e.slice(0, 16).reduce((a, b) => a + b, 0) % 3;
+      const remainder = Math.sumPrecise(e.slice(0, 16)) % 3;
       if (remainder === 0) {
         k = calculateSHA256(e, 0, e.length);
       } else if (remainder === 1) {

src/core/glyf.js

@@ -81,11 +81,10 @@ class GlyfTable {
   }
 
   getSize() {
-    return this.glyphs.reduce((a, g) => {
-      const size = g.getSize();
+    return Math.sumPrecise(
       // Round to next multiple of 4 if needed.
-      return a + ((size + 3) & ~3);
-    }, 0);
+      this.glyphs.map(g => (g.getSize() + 3) & ~3)
+    );
   }
 
   write() {
@@ -169,7 +168,7 @@ class Glyph {
     }
     const size = this.simple
       ? this.simple.getSize()
-      : this.composites.reduce((a, c) => a + c.getSize(), 0);
+      : Math.sumPrecise(this.composites.map(c => c.getSize()));
     return this.header.getSize() + size;
   }
 

src/core/writer.js

@@ -184,7 +184,7 @@ function computeMD5(filesize, xrefInfo) {
     filesize.toString(),
     ...Object.values(xrefInfo.info),
   ];
-  const md5BufferLen = md5Buffer.reduce((a, str) => a + str.length, 0);
+  const md5BufferLen = Math.sumPrecise(md5Buffer.map(str => str.length));
 
   const array = new Uint8Array(md5BufferLen);
   let offset = 0;
@@ -352,7 +352,7 @@ async function getXRefStreamTable(
   newXref.set("W", sizes);
   computeIDs(baseOffset, xrefInfo, newXref);
 
-  const structSize = sizes.reduce((a, x) => a + x, 0);
+  const structSize = Math.sumPrecise(sizes);
   const data = new Uint8Array(structSize * xrefTableData.length);
   const stream = new Stream(data);
   stream.dict = newXref;
@@ -467,10 +467,8 @@ async function incrementalUpdate({
     ? getXRefStreamTable(xrefInfo, baseOffset, newRefs, newXref, buffer)
     : getXRefTable(xrefInfo, baseOffset, newRefs, newXref, buffer));
 
-  const totalLength = buffer.reduce(
-    (a, str) => a + str.length,
-    originalData.length
-  );
+  const totalLength =
+    originalData.length + Math.sumPrecise(buffer.map(str => str.length));
   const array = new Uint8Array(totalLength);
 
   // Original data

src/core/xfa/html_utils.js

@@ -86,14 +86,15 @@ const converters = {
       const colSpan = node.colSpan;
       let w;
       if (colSpan === -1) {
-        w = extra.columnWidths
-          .slice(extra.currentColumn)
-          .reduce((a, x) => a + x, 0);
+        w = Math.sumPrecise(extra.columnWidths.slice(extra.currentColumn));
         extra.currentColumn = 0;
       } else {
-        w = extra.columnWidths
-          .slice(extra.currentColumn, extra.currentColumn + colSpan)
-          .reduce((a, x) => a + x, 0);
+        w = Math.sumPrecise(
+          extra.columnWidths.slice(
+            extra.currentColumn,
+            extra.currentColumn + colSpan
+          )
+        );
         extra.currentColumn =
           (extra.currentColumn + node.colSpan) % extra.columnWidths.length;
       }
@@ -328,13 +329,14 @@ function fixDimensions(node) {
     const colSpan = node.colSpan;
     let width;
     if (colSpan === -1) {
-      width = extra.columnWidths
-        .slice(extra.currentColumn)
-        .reduce((a, w) => a + w, 0);
+      width = Math.sumPrecise(extra.columnWidths.slice(extra.currentColumn));
     } else {
-      width = extra.columnWidths
-        .slice(extra.currentColumn, extra.currentColumn + colSpan)
-        .reduce((a, w) => a + w, 0);
+      width = Math.sumPrecise(
+        extra.columnWidths.slice(
+          extra.currentColumn,
+          extra.currentColumn + colSpan
+        )
+      );
     }
     if (!isNaN(width)) {
       node.w = width;
@@ -348,7 +350,7 @@ function fixDimensions(node) {
 
   if (node.layout === "table") {
     if (node.w === "" && Array.isArray(node.columnWidths)) {
-      node.w = node.columnWidths.reduce((a, x) => a + x, 0);
+      node.w = Math.sumPrecise(node.columnWidths);
     }
   }
 }

src/core/xfa/layout.js

@@ -183,9 +183,9 @@ function getAvailableSpace(node) {
       };
     case "rl-row":
     case "row":
-      const width = node[$extra].columnWidths
-        .slice(node[$extra].currentColumn)
-        .reduce((a, x) => a + x);
+      const width = Math.sumPrecise(
+        node[$extra].columnWidths.slice(node[$extra].currentColumn)
+      );
       return { width, height: availableSpace.height - marginH };
     case "table":
     case "tb":

src/display/editor/freetext.js

@@ -718,7 +718,7 @@ class FreeTextEditor extends AnnotationEditor {
 
     // Set the caret at the right position.
     const newRange = new Range();
-    let beforeLength = bufferBefore.reduce((acc, line) => acc + line.length, 0);
+    let beforeLength = Math.sumPrecise(bufferBefore.map(line => line.length));
     for (const { firstChild } of this.editorDiv.childNodes) {
       // Each child is either a div with a text node or a br element.
       if (firstChild.nodeType === Node.TEXT_NODE) {

src/shared/util.js

@@ -1130,6 +1130,16 @@ if (
   };
 }
 
+// TODO: Remove this once the `javascript.options.experimental.math_sumprecise`
+//       preference is removed from Firefox.
+if (typeof Math.sumPrecise !== "function") {
+  // Note that this isn't a "proper" polyfill, but since we're only using it to
+  // replace `Array.prototype.reduce()` invocations it should be fine.
+  Math.sumPrecise = function (numbers) {
+    return numbers.reduce((a, b) => a + b, 0);
+  };
+}
+
 if (
   typeof PDFJSDev !== "undefined" &&
   !PDFJSDev.test("SKIP_BABEL") &&

test/unit/pdf_find_controller_spec.js

@@ -128,7 +128,7 @@ function testSearch({
       }
     }
 
-    const totalMatches = matchesPerPage.reduce((a, b) => a + b);
+    const totalMatches = Math.sumPrecise(matchesPerPage);
 
     if (updateFindControlState) {
       eventBus.on(