-
Notifications
You must be signed in to change notification settings - Fork 30k
Commit
This commit does not belong to any branch on this repository, and may belong to a fork outside of the repository.
This tests that the hash seed used by V8 for hashing is random. PR-URL: https://github.com/nodejs/node-private/pull/84 Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl> Reviewed-By: Michael Dawson <michael_dawson@ca.ibm.com> Reviewed-By: Fedor Indutny <fedor.indutny@gmail.com>
- Loading branch information
1 parent
51d69d2
commit 803d689
Showing
3 changed files
with
200 additions
and
1 deletion.
There are no files selected for viewing
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
Original file line number | Diff line number | Diff line change |
---|---|---|
@@ -0,0 +1,175 @@ | ||
/* eslint-disable required-modules */ | ||
'use strict'; | ||
function min(arr) { | ||
let res = arr[0]; | ||
for (let i = 1; i < arr.length; i++) { | ||
const val = arr[i]; | ||
if (val < res) | ||
res = val; | ||
} | ||
return res; | ||
} | ||
function run_repeated(n, fn) { | ||
const res = []; | ||
for (let i = 0; i < n; i++) res.push(fn()); | ||
return res; | ||
} | ||
|
||
const INT_MAX = 0x7fffffff; | ||
|
||
// from src/js/collection.js | ||
// key must be a signed 32-bit number! | ||
function ComputeIntegerHash(key/*, seed*/) { | ||
let hash = key; | ||
hash = hash ^ 0/*seed*/; | ||
hash = ~hash + (hash << 15); // hash = (hash << 15) - hash - 1; | ||
hash = hash ^ (hash >>> 12); | ||
hash = hash + (hash << 2); | ||
hash = hash ^ (hash >>> 4); | ||
hash = (hash * 2057) | 0; // hash = (hash + (hash << 3)) + (hash << 11); | ||
hash = hash ^ (hash >>> 16); | ||
return hash & 0x3fffffff; | ||
} | ||
|
||
const kNofHashBitFields = 2; | ||
const kHashShift = kNofHashBitFields; | ||
const kHashBitMask = 0xffffffff >>> kHashShift; | ||
const kZeroHash = 27; | ||
|
||
function string_to_array(str) { | ||
const res = new Array(str.length); | ||
for (let i = 0; i < str.length; i++) { | ||
res[i] = str.charCodeAt(i); | ||
} | ||
return res; | ||
} | ||
|
||
function gen_specialized_hasher(str) { | ||
const str_arr = string_to_array(str); | ||
return Function('seed', ` | ||
var running_hash = seed; | ||
${str_arr.map((c) => ` | ||
running_hash += ${c}; | ||
running_hash &= 0xffffffff; | ||
running_hash += (running_hash << 10); | ||
running_hash &= 0xffffffff; | ||
running_hash ^= (running_hash >>> 6); | ||
running_hash &= 0xffffffff; | ||
`).join('')} | ||
running_hash += (running_hash << 3); | ||
running_hash &= 0xffffffff; | ||
running_hash ^= (running_hash >>> 11); | ||
running_hash &= 0xffffffff; | ||
running_hash += (running_hash << 15); | ||
running_hash &= 0xffffffff; | ||
if ((running_hash & ${kHashBitMask}) == 0) { | ||
return ${kZeroHash}; | ||
} | ||
return running_hash; | ||
`); | ||
} | ||
|
||
// adapted from HashToEntry | ||
function hash_to_bucket(hash, numBuckets) { | ||
return (hash & ((numBuckets) - 1)); | ||
} | ||
|
||
function time_set_lookup(set, value) { | ||
const t1 = process.hrtime(); | ||
for (let i = 0; i < 100; i++) { | ||
// annoyingly, SetHas() is JS code and therefore potentially optimizable. | ||
// However, SetHas() looks up the table using native code, and it seems like | ||
// that's sufficient to prevent the optimizer from doing anything? | ||
set.has(value); | ||
} | ||
const t = process.hrtime(t1); | ||
const secs = t[0]; | ||
const nanos = t[1]; | ||
return secs * 1e9 + nanos; | ||
} | ||
|
||
// Set with 256 buckets; bucket 0 full, others empty | ||
const tester_set_buckets = 256; | ||
const tester_set = new Set(); | ||
let tester_set_treshold; | ||
(function() { | ||
// fill bucket 0 and find extra numbers mapping to bucket 0 and a different | ||
// bucket `capacity == numBuckets * 2` | ||
let needed = Math.floor(tester_set_buckets * 1.5) + 1; | ||
let positive_test_value; | ||
let negative_test_value; | ||
for (let i = 0; true; i++) { | ||
if (i > INT_MAX) throw new Error('i too high'); | ||
if (hash_to_bucket(ComputeIntegerHash(i), tester_set_buckets) !== 0) { | ||
negative_test_value = i; | ||
break; | ||
} | ||
} | ||
for (let i = 0; needed > 0; i++) { | ||
if (i > INT_MAX) throw new Error('i too high'); | ||
if (hash_to_bucket(ComputeIntegerHash(i), tester_set_buckets) === 0) { | ||
needed--; | ||
if (needed == 0) { | ||
positive_test_value = i; | ||
} else { | ||
tester_set.add(i); | ||
} | ||
} | ||
} | ||
|
||
// calibrate Set access times for accessing the full bucket / an empty bucket | ||
const pos_time = | ||
min(run_repeated(10000, time_set_lookup.bind(null, tester_set, | ||
positive_test_value))); | ||
const neg_time = | ||
min(run_repeated(10000, time_set_lookup.bind(null, tester_set, | ||
negative_test_value))); | ||
tester_set_treshold = (pos_time + neg_time) / 2; | ||
// console.log(`pos_time: ${pos_time}, neg_time: ${neg_time},`, | ||
// `threshold: ${tester_set_treshold}`); | ||
})(); | ||
|
||
// determine hash seed | ||
const slow_str_gen = (function*() { | ||
let strgen_i = 0; | ||
outer: | ||
while (1) { | ||
const str = '#' + (strgen_i++); | ||
for (let i = 0; i < 1000; i++) { | ||
if (time_set_lookup(tester_set, str) < tester_set_treshold) | ||
continue outer; | ||
} | ||
yield str; | ||
} | ||
})(); | ||
|
||
const first_slow_str = slow_str_gen.next().value; | ||
// console.log('first slow string:', first_slow_str); | ||
const first_slow_str_special_hasher = gen_specialized_hasher(first_slow_str); | ||
let seed_candidates = []; | ||
//var t_before_first_seed_brute = performance.now(); | ||
for (let seed_candidate = 0; seed_candidate < 0x100000000; seed_candidate++) { | ||
if (hash_to_bucket(first_slow_str_special_hasher(seed_candidate), | ||
tester_set_buckets) == 0) { | ||
seed_candidates.push(seed_candidate); | ||
} | ||
} | ||
// console.log(`got ${seed_candidates.length} candidates`); | ||
// after ${performance.now()-t_before_first_seed_brute} | ||
while (seed_candidates.length > 1) { | ||
const slow_str = slow_str_gen.next().value; | ||
const special_hasher = gen_specialized_hasher(slow_str); | ||
const new_seed_candidates = []; | ||
for (const seed_candidate of seed_candidates) { | ||
if (hash_to_bucket(special_hasher(seed_candidate), tester_set_buckets) == | ||
0) { | ||
new_seed_candidates.push(seed_candidate); | ||
} | ||
} | ||
seed_candidates = new_seed_candidates; | ||
// console.log(`reduced to ${seed_candidates.length} candidates`); | ||
} | ||
if (seed_candidates.length != 1) | ||
throw new Error('no candidates remaining'); | ||
const seed = seed_candidates[0]; | ||
console.log(seed); |
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
Original file line number | Diff line number | Diff line change |
---|---|---|
@@ -0,0 +1,20 @@ | ||
'use strict'; | ||
|
||
const REPETITIONS = 2; | ||
|
||
const assert = require('assert'); | ||
const common = require('../common'); | ||
const cp = require('child_process'); | ||
const path = require('path'); | ||
const targetScript = path.resolve(common.fixturesDir, 'guess-hash-seed.js'); | ||
const seeds = []; | ||
|
||
for (let i = 0; i < REPETITIONS; ++i) { | ||
const seed = cp.spawnSync(process.execPath, [targetScript], | ||
{ encoding: 'utf8' }).stdout.trim(); | ||
seeds.push(seed); | ||
} | ||
|
||
console.log(`Seeds: ${seeds}`); | ||
const hasDuplicates = (new Set(seeds)).size !== seeds.length; | ||
assert.strictEqual(hasDuplicates, false); |