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assert: improve deepEqual Set and Map worst case
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This change improves the algorithm for the worst case from O(n^2)
to O(n log n) by using a lazily initiated set with object or
not strict equal primitives keys.

In addition a few comments got fixed and a statement simplified.

PR-URL: #14258
Reviewed-By: Refael Ackermann <refack@gmail.com>
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@BridgeAR @addaleax
BridgeAR authored and addaleax committed Jul 28, 2017
1 parent 9252b8c commit e2356e7
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Showing 2 changed files with 254 additions and 86 deletions.
255 changes: 170 additions & 85 deletions lib/assert.js
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Original file line number Diff line number Diff line change
Expand Up @@ -33,11 +33,6 @@ const errors = require('internal/errors');

const assert = module.exports = ok;

// At present only the three keys mentioned above are used and
// understood by the spec. Implementations or sub modules can pass
// other keys to the AssertionError's constructor - they will be
// ignored.

// All of the following functions must throw an AssertionError
// when a corresponding condition is not met, with a message that
// may be undefined if not provided. All assertion methods provide
Expand Down Expand Up @@ -112,9 +107,9 @@ function areSimilarRegExps(a, b) {
return a.source === b.source && a.flags === b.flags;
}

// For small buffers it's faster to compare the buffer in a loop.
// The c++ barrier takes the advantage of the faster compare otherwise.
// 300 was the number after which compare became faster.
// For small buffers it's faster to compare the buffer in a loop. The c++
// barrier including the Buffer.from operation takes the advantage of the faster
// compare otherwise. 300 was the number after which compare became faster.
function areSimilarTypedArrays(a, b) {
const len = a.byteLength;
if (len !== b.byteLength) {
Expand Down Expand Up @@ -221,21 +216,15 @@ function looseDeepEqual(actual, expected) {
return false;
}
if (util.isDate(actual) && util.isDate(expected)) {
if (actual.getTime() !== expected.getTime()) {
return false;
}
return true;
return actual.getTime() === expected.getTime();
}
if (util.isRegExp(actual) && util.isRegExp(expected)) {
if (!areSimilarRegExps(actual, expected)) {
return false;
}
return true;
return areSimilarRegExps(actual, expected);
}
const actualTag = objectToString(actual);
const expectedTag = objectToString(expected);
if (actualTag === expectedTag) {
if (!isFloatTypedArrayTag(actualTag) && !isObjectOrArrayTag(actualTag) &&
if (!isObjectOrArrayTag(actualTag) && !isFloatTypedArrayTag(actualTag) &&
ArrayBuffer.isView(actual)) {
return areSimilarTypedArrays(actual, expected);
}
Expand Down Expand Up @@ -314,29 +303,38 @@ function innerDeepEqual(actual, expected, strict, memos) {
return areEq;
}

function setHasSimilarElement(set, val1, usedEntries, strict, memo) {
if (set.has(val1)) {
if (usedEntries !== null)
usedEntries.add(val1);
return true;
}

// In strict mode the only things which can match a primitive or a function
// will already be detected by set.has(val1).
if (strict && (typeof val1 !== 'object' || val1 === null))
return false;

// Otherwise go looking.
function setHasEqualElement(set, val1, strict, memo) {
// Go looking.
for (const val2 of set) {
if (!usedEntries.has(val2) && innerDeepEqual(val1, val2, strict, memo)) {
usedEntries.add(val2);
if (innerDeepEqual(val1, val2, strict, memo)) {
// Remove the matching element to make sure we do not check that again.
set.delete(val2);
return true;
}
}

return false;
}

// Note: we actually run this multiple times for each loose key!
// This is done to prevent slowing down the average case.
function setHasLoosePrim(a, b, val) {
const altValues = findLooseMatchingPrimitives(val);
if (altValues === undefined)
return false;

var matches = 1;
for (var i = 0; i < altValues.length; i++) {
if (b.has(altValues[i])) {
matches--;
}
if (a.has(altValues[i])) {
matches++;
}
}
return matches === 0;
}

function setEquiv(a, b, strict, memo) {
// This code currently returns false for this pair of sets:
// assert.deepEqual(new Set(['1', 1]), new Set([1]))
Expand All @@ -348,59 +346,124 @@ function setEquiv(a, b, strict, memo) {
if (a.size !== b.size)
return false;

// This is a set of the entries in b which have been consumed in our pairwise
// comparison.
//
// This is a lazily initiated Set of entries which have to be compared
// pairwise.
var set = null;
// When the sets contain only value types (eg, lots of numbers), and we're in
// strict mode, we don't need to match off the entries in a pairwise way. In
// that case this initialization is done lazily to avoid the allocation &
// bookkeeping cost. Unfortunately, we can't get away with that in non-strict
// mode.
let usedEntries = strict === true ? null : new Set();

for (const val1 of a) {
if (usedEntries === null && typeof val1 === 'object')
usedEntries = new Set();

// If the value doesn't exist in the second set by reference, and its an
// object or an array we'll need to go hunting for something thats
// deep-equal to it. Note that this is O(n^2) complexity, and will get
// slower if large, very similar sets / maps are nested inside.
// Unfortunately there's no real way around this.
if (!setHasSimilarElement(b, val1, usedEntries, strict, memo))
// strict mode or if all entries strictly match, we don't need to match the
// entries in a pairwise way. In that case this initialization is done lazily
// to avoid the allocation & bookkeeping cost.
for (const val of a) {
// Note: Checking for the objects first improves the performance for object
// heavy sets but it is a minor slow down for primitives. As they are fast
// to check this improves the worst case scenario instead.
if (typeof val === 'object' && val !== null) {
if (set === null) {
set = new Set();
}
// If the specified value doesn't exist in the second set its an not null
// object (or non strict only: a not matching primitive) we'll need to go
// hunting for something thats deep-(strict-)equal to it. To make this
// O(n log n) complexity we have to copy these values in a new set first.
set.add(val);
} else if (!b.has(val) && (strict || !setHasLoosePrim(a, b, val))) {
return false;
}
}

if (set !== null) {
for (const val of b) {
// In non-strict-mode we have to check if a primitive value is already
// matching and only if it's not, go hunting for it.
if (typeof val === 'object' && val !== null) {
if (!setHasEqualElement(set, val, strict, memo))
return false;
} else if (!a.has(val) && (strict || !setHasLoosePrim(b, a, val))) {
return false;
}
}
}

return true;
}

function mapHasSimilarEntry(map, key1, item1, usedEntries, strict, memo) {
// To be able to handle cases like:
// Map([[1, 'a'], ['1', 'b']]) vs Map([['1', 'a'], [1, 'b']])
// or:
// Map([[{}, 'a'], [{}, 'b']]) vs Map([[{}, 'b'], [{}, 'a']])
// ... we need to consider *all* matching keys, not just the first we find.
function findLooseMatchingPrimitives(prim) {
var values, number;
switch (typeof prim) {
case 'number':
values = ['' + prim];
if (prim === 1 || prim === 0)
values.push(Boolean(prim));
return values;
case 'string':
number = +prim;
if ('' + number === prim) {
values = [number];
if (number === 1 || number === 0)
values.push(Boolean(number));
}
return values;
case 'undefined':
return [null];
case 'object': // Only pass in null as object!
return [undefined];
case 'boolean':
number = +prim;
return [number, '' + number];
}
}

// This check is not strictly necessary. The loop performs this check, but
// doing it here improves performance of the common case when reference-equal
// keys exist (which includes all primitive-valued keys).
if (map.has(key1) && innerDeepEqual(item1, map.get(key1), strict, memo)) {
if (usedEntries !== null)
usedEntries.add(key1);
return true;
// This is a ugly but relatively fast way to determine if a loose equal entry
// actually has a correspondent matching entry. Otherwise checking for such
// values would be way more expensive (O(n^2)).
// Note: we actually run this multiple times for each loose key!
// This is done to prevent slowing down the average case.
function mapHasLoosePrim(a, b, key1, memo, item1, item2) {
const altKeys = findLooseMatchingPrimitives(key1);
if (altKeys === undefined)
return false;

const setA = new Set();
const setB = new Set();

var keyCount = 1;

setA.add(item1);
if (b.has(key1)) {
keyCount--;
setB.add(item2);
}

if (strict && (typeof key1 !== 'object' || key1 === null))
for (var i = 0; i < altKeys.length; i++) {
const key2 = altKeys[i];
if (a.has(key2)) {
keyCount++;
setA.add(a.get(key2));
}
if (b.has(key2)) {
keyCount--;
setB.add(b.get(key2));
}
}
if (keyCount !== 0 || setA.size !== setB.size)
return false;

for (const [key2, item2] of map) {
// The first part is checked above.
if (key2 === key1 || usedEntries.has(key2))
continue;
for (const val of setA) {
if (!setHasEqualElement(setB, val, false, memo))
return false;
}

return true;
}

function mapHasEqualEntry(set, map, key1, item1, strict, memo) {
// To be able to handle cases like:
// Map([[{}, 'a'], [{}, 'b']]) vs Map([[{}, 'b'], [{}, 'a']])
// ... we need to consider *all* matching keys, not just the first we find.
for (const key2 of set) {
if (innerDeepEqual(key1, key2, strict, memo) &&
innerDeepEqual(item1, item2, strict, memo)) {
usedEntries.add(key2);
innerDeepEqual(item1, map.get(key2), strict, memo)) {
set.delete(key2);
return true;
}
}
Expand All @@ -411,21 +474,45 @@ function mapHasSimilarEntry(map, key1, item1, usedEntries, strict, memo) {
function mapEquiv(a, b, strict, memo) {
// Caveat: In non-strict mode, this implementation does not handle cases
// where maps contain two equivalent-but-not-reference-equal keys.
//
// For example, maps like this are currently considered not equivalent:
if (a.size !== b.size)
return false;

let usedEntries = strict === true ? null : new Set();

for (const [key, item] of a) {
if (usedEntries === null && typeof key === 'object')
usedEntries = new Set();

// Just like setEquiv above, this hunt makes this function O(n^2) when
// using objects and lists as keys
if (!mapHasSimilarEntry(b, key, item, usedEntries, strict, memo))
var set = null;

for (const [key, item1] of a) {
// By directly retrieving the value we prevent another b.has(key) check in
// almost all possible cases.
const item2 = b.get(key);
if (item2 === undefined) {
// Just like setEquiv above but in addition we have to make sure the
// values are also equal.
if (typeof key === 'object' && key !== null) {
if (set === null) {
set = new Set();
}
set.add(key);
// Note: we do not have to pass memo in this case as at least one item
// is undefined.
} else if ((!innerDeepEqual(item1, item2, strict) || !b.has(key)) &&
(strict || !mapHasLoosePrim(a, b, key, memo, item1))) {
return false;
}
} else if (!innerDeepEqual(item1, item2, strict, memo) &&
(strict || !mapHasLoosePrim(a, b, key, memo, item1, item2))) {
return false;
}
}

if (set !== null) {
for (const [key, item] of b) {
if (typeof key === 'object' && key !== null) {
if (!mapHasEqualEntry(set, a, key, item, strict, memo))
return false;
} else if (!a.has(key) &&
(strict || !mapHasLoosePrim(b, a, key, memo, item))) {
return false;
}
}
}

return true;
Expand All @@ -437,12 +524,10 @@ function objEquiv(a, b, strict, keys, memos) {
if (isSet(a)) {
if (!isSet(b) || !setEquiv(a, b, strict, memos))
return false;
} else if (isSet(b)) {
return false;
} else if (isMap(a)) {
if (!isMap(b) || !mapEquiv(a, b, strict, memos))
return false;
} else if (isMap(b)) {
} else if (isSet(b) || isMap(b)) {
return false;
}

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