From: Greg Hurrell <greg@hurrell.net>
Date: Sun, 2 Aug 2015 06:19:05 +0000 (-0700)
Subject: Massive speed-up by avoiding Chrome de-opt in hottest function
X-Git-Url: https://git.wincent.com/hextrapolate.git/commitdiff_plain/ea6db33a7d3d8923feb89f221785d0b4ed913f48

Massive speed-up by avoiding Chrome de-opt in hottest function

I became suspicious of the Math calls thanks to this thread:

https://groups.google.com/forum/#!msg/google-chrome-developer-tools/Y0J2XQ9iiqU/H60qqZNlQa8J

Turns out, those were the culprit.
---

diff --git a/src/addDigits.js b/src/addDigits.js
index 4a3de34..27d998e 100644
--- a/src/addDigits.js
+++ b/src/addDigits.js
@@ -14,16 +14,15 @@ export default function addDigits(
 ): Array<number> {
   let result = [];
   let carry = 0;
-  for (
-    let i = 0, max = Math.max(aDigits.length, bDigits.length);
-    i < max || carry;
-    i++
-  ) {
-    const aDigit = aDigits[i] || 0;
-    const bDigit = bDigits[i] || 0;
+  for (let i = 0; i < aDigits.length || i < bDigits.length || carry; i++) {
+    const aDigit = i < aDigits.length ? aDigits[i] : 0;
+    const bDigit = i < bDigits.length ? bDigits[i] : 0;
     const sum = aDigit + bDigit + carry;
     result.push(sum % base);
-    carry = Math.floor(sum / base);
+
+    // ~~ here is the equivalent of Math.floor; used to avoid V8 de-opt,
+    // "Reference to a variable which requires dynamic lookup".
+    carry = ~~(sum / base);
   }
   return result.length ? result : [0];
 }