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events: simplify stack compare function #24744

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events: simplify stack compare function #24744

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events: simplify stack compare function
BridgeAR Nov 18, 2018
11a6984
fixup: improve comments
BridgeAR Nov 30, 2018
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fixup: improve comments
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@BridgeAR
BridgeAR committed Nov 30, 2018
commit 11a6984df6153a308790919539be4c254a318369
4 changes: 2 additions & 2 deletions lib/events.js
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Expand Up @@ -107,14 +107,14 @@ EventEmitter.prototype.getMaxListeners = function getMaxListeners() {
// appears in `b` with a length of at least 4.
function identicalSequenceRange(a, b) {
for (var i = 0; i < a.length - 3; i++) {
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@mcollina mcollina Dec 7, 2018

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I would cache a.length - 3 in a variable.

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@targos targos Dec 7, 2018

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why?

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@BridgeAR BridgeAR Dec 7, 2018

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I expect the value to be constant fold (but I did not check).

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@mcollina mcollina Dec 7, 2018

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a could be quite big, and it used to be slightly faster to cache the value if it's computed.

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@BridgeAR BridgeAR Dec 7, 2018

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a should normally be small (we currently only use this for stack frames) and this implementation should also be faster than the one before. If it's about performance, I could save a couple comparisons by using a simple for loop instead of indexOf (currently I check until the last entry but the last three entries are not interesting).

@bmeurer do values like these get constant fold?

// Find the first occurrence of the frame that could match up to four
// frames.
// Find the first entry of b that matches the current entry of a.
const pos = b.indexOf(a[i]);
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if (pos !== -1) {
const rest = b.length - pos;
if (rest > 3) {
let len = 1;
const maxLen = Math.min(a.length - i, rest);
// Count the number of consecutive entries.
while (maxLen > len && a[i + len] === b[pos + len]) {
len++;
}
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