hughfdjackson
commented
11 years ago owing to issue discussed in commit e77ef622fbaa4faaaa3bf1a5291e5527996f937d, these need to be re-run.
To Test:
- Actual implementation of java's String#hashCode.
// hash function for strings, based on Java's String.hashCode:
// http://docs.oracle.com/javase/1.4.2/docs/api/java/lang/String.html#hashCode()
var hash = function(str){
var h = 0
var l = str.length
for ( var i = 0; i < l; i += 1 )
h = h * 31 + str.charCodeAt(i)
return h
}- Bad implementation of java's String#hashCode
// http://docs.oracle.com/javase/1.4.2/docs/api/java/lang/String.html#hashCode()
var hash = function(str){
var h = 0
var l = str.length
for ( var i = 0; i < l; i += 1 )
h += str.charCodeAt(i) * 31 * l - i
return h
}- chash - npm module:
var max32bit = 0x7fffffff
var hash = require('chash')
// to allow hooks for other implementations/tests to override the default
// hash and equality functions (which are the necessary ones for creating
// hash-table-like behaviour, as the hash-trie has), they can be passed in
// as opts to the CRUD functions. The default ones covers the 80% use-case
var defaultOpts = {
eq : function(a, b){ return a === b },
hash: function(str){
return hash(str, max32bit)
}
}- Sedgewick universal hash:
// hash function
var hash = function(s) {
var b = 27183
var a = 31415
var h = 0
var tableSize = 0x7fffff
for (var i = 0; i < s.length; i++) {
h = (a * h + s[i].charCodeAt()) % tableSize;
a = ((a % tableSize) * (b % tableSize)) % (tableSize);
}
return h;
}- Zobel:
// hash function
// based on J. Zobel (2001)
// http://www.seg.rmit.edu.au/code/zwh-ipl/bitwisehash.c
var max32bit = 2 ^ 32
var hash = function(str){
var hash = 0
for ( var i = 0; i < str.length; i += 1 )
hash ^= ( hash << 5) + str[i] + (hash >> 2)
return hash % 32
}
Test the relative perf of different hashing functions, to pick one for use as the default hash. Should produce a hash usable with hashMask (i.e. one that produces at least a 32 bit hash)