githubmirror/immutable-js

src/Hash.js
257 строк7 KB
Julien Deniau
perf(Map): index large hash-collision buckets for faster lookups
26 июн 2026, 01:49
26 июн 2026, 01:493dd7e56
import { smi } from './Math';

const defaultValueOf = Object.prototype.valueOf;

export function hash(o) {
  if (o == null) {
    return hashNullish(o);
  }

  if (typeof o.hashCode === 'function') {
    // Drop any high bits from accidentally long hash codes.
    return smi(o.hashCode(o));
  }

  const v = valueOf(o);

  if (v == null) {
    return hashNullish(v);
  }

  switch (typeof v) {
    case 'boolean':
      // The hash values for built-in constants are a 1 value for each 5-byte
      // shift region expect for the first, which encodes the value. This
      // reduces the odds of a hash collision for these common values.
      return v ? 0x42108421 : 0x42108420;
    case 'number':
      return hashNumber(v);
    case 'string':
      return v.length > STRING_HASH_CACHE_MIN_STRLEN
        ? cachedHashString(v)
        : hashString(v);
    case 'object':
    case 'function':
      return hashJSObj(v);
    case 'symbol':
      return hashSymbol(v);
    default:
      if (typeof v.toString === 'function') {
        return hashString(v.toString());
      }
      throw new Error('Value type ' + typeof v + ' cannot be hashed.');
  }
}

function hashNullish(nullish) {
  return nullish === null ? 0x42108422 : /* undefined */ 0x42108423;
}

// Compress arbitrarily large numbers into smi hashes.
function hashNumber(n) {
  if (n !== n || n === Infinity) {
    return 0;
  }
  let hash = n | 0;
  if (hash !== n) {
    hash ^= n * 0xffffffff;
  }
  while (n > 0xffffffff) {
    n /= 0xffffffff;
    hash ^= n;
  }
  return smi(hash);
}

function cachedHashString(string) {
  let hashed = stringHashCache[string];
  if (hashed === undefined) {
    hashed = hashString(string);
    if (STRING_HASH_CACHE_SIZE === STRING_HASH_CACHE_MAX_SIZE) {
      STRING_HASH_CACHE_SIZE = 0;
      stringHashCache = {};
    }
    STRING_HASH_CACHE_SIZE++;
    stringHashCache[string] = hashed;
  }
  return hashed;
}

// http://jsperf.com/hashing-strings
function hashString(string) {
  // This is the hash from JVM
  // The hash code for a string is computed as
  // s[0] * 31 ^ (n - 1) + s[1] * 31 ^ (n - 2) + ... + s[n - 1],
  // where s[i] is the ith character of the string and n is the length of
  // the string. We "mod" the result to make it between 0 (inclusive) and 2^31
  // (exclusive) by dropping high bits.
  let hashed = 0;
  for (let ii = 0; ii < string.length; ii++) {
    hashed = (31 * hashed + string.charCodeAt(ii)) | 0;
  }
  return smi(hashed);
}

// Per-process seed for the secondary collision hash. Never exposed nor
// serialized, so the public `hash()` stays deterministic. An odd base in
// [3, 2^20) keeps `base * h` exact as a double (no `Math.imul`).
const COLLISION_HASH_BASE =
  ((Math.random() * 0x100000) | 1) % 0x100000 || 0x9e37;

// Secondary hash to index entries within a `HashCollisionNode`, where every key
// shares the same primary `hash()`. Using a different, seeded base scatters
// crafted collision families (e.g. "Aa"/"BB", which only collide under base 31)
// that an attacker cannot precompute without the seed. It only narrows
// candidates — `is()` still decides equality — so non-string keys can safely
// fall back to the (here constant) primary hash and a linear scan.
export function hashCollisionKey(key) {
  if (typeof key !== 'string') {
    return hash(key);
  }
  let hashed = 0;
  for (let ii = 0; ii < key.length; ii++) {
    hashed = (COLLISION_HASH_BASE * hashed + key.charCodeAt(ii)) | 0;
  }
  return hashed;
}

function hashSymbol(sym) {
  let hashed = symbolMap[sym];
  if (hashed !== undefined) {
    return hashed;
  }

  hashed = nextHash();

  symbolMap[sym] = hashed;

  return hashed;
}

function hashJSObj(obj) {
  let hashed;
  if (usingWeakMap) {
    hashed = weakMap.get(obj);
    if (hashed !== undefined) {
      return hashed;
    }
  }

  hashed = obj[UID_HASH_KEY];
  if (hashed !== undefined) {
    return hashed;
  }

  if (!canDefineProperty) {
    hashed = obj.propertyIsEnumerable && obj.propertyIsEnumerable[UID_HASH_KEY];
    if (hashed !== undefined) {
      return hashed;
    }

    hashed = getIENodeHash(obj);
    if (hashed !== undefined) {
      return hashed;
    }
  }

  hashed = nextHash();

  if (usingWeakMap) {
    weakMap.set(obj, hashed);
  } else if (isExtensible !== undefined && isExtensible(obj) === false) {
    throw new Error('Non-extensible objects are not allowed as keys.');
  } else if (canDefineProperty) {
    Object.defineProperty(obj, UID_HASH_KEY, {
      enumerable: false,
      configurable: false,
      writable: false,
      value: hashed,
    });
  } else if (
    obj.propertyIsEnumerable !== undefined &&
    obj.propertyIsEnumerable === obj.constructor.prototype.propertyIsEnumerable
  ) {
    // Since we can't define a non-enumerable property on the object
    // we'll hijack one of the less-used non-enumerable properties to
    // save our hash on it. Since this is a function it will not show up in
    // `JSON.stringify` which is what we want.
    obj.propertyIsEnumerable = function () {
      return this.constructor.prototype.propertyIsEnumerable.apply(
        this,
        arguments
      );
    };
    obj.propertyIsEnumerable[UID_HASH_KEY] = hashed;
  } else if (obj.nodeType !== undefined) {
    // At this point we couldn't get the IE `uniqueID` to use as a hash
    // and we couldn't use a non-enumerable property to exploit the
    // dontEnum bug so we simply add the `UID_HASH_KEY` on the node
    // itself.
    obj[UID_HASH_KEY] = hashed;
  } else {
    throw new Error('Unable to set a non-enumerable property on object.');
  }

  return hashed;
}

// Get references to ES5 object methods.
const isExtensible = Object.isExtensible;

// True if Object.defineProperty works as expected. IE8 fails this test.
const canDefineProperty = (function () {
  try {
    Object.defineProperty({}, '@', {});
    return true;
  } catch (e) {
    return false;
  }
})();

// IE has a `uniqueID` property on DOM nodes. We can construct the hash from it
// and avoid memory leaks from the IE cloneNode bug.
function getIENodeHash(node) {
  if (node && node.nodeType > 0) {
    switch (node.nodeType) {
      case 1: // Element
        return node.uniqueID;
      case 9: // Document
        return node.documentElement && node.documentElement.uniqueID;
    }
  }
}

function valueOf(obj) {
  return obj.valueOf !== defaultValueOf && typeof obj.valueOf === 'function'
    ? obj.valueOf(obj)
    : obj;
}

function nextHash() {
  const nextHash = ++_objHashUID;
  if (_objHashUID & 0x40000000) {
    _objHashUID = 0;
  }
  return nextHash;
}

// If possible, use a WeakMap.
const usingWeakMap = typeof WeakMap === 'function';
let weakMap;
if (usingWeakMap) {
  weakMap = new WeakMap();
}

const symbolMap = Object.create(null);

let _objHashUID = 0;

let UID_HASH_KEY = '__immutablehash__';
if (typeof Symbol === 'function') {
  UID_HASH_KEY = Symbol(UID_HASH_KEY);
}

const STRING_HASH_CACHE_MIN_STRLEN = 16;
const STRING_HASH_CACHE_MAX_SIZE = 255;
let STRING_HASH_CACHE_SIZE = 0;
let stringHashCache = {};