Use FNV hash for Key

[lahma]

• https://en.wikipedia.org/wiki/Fowler%E2%80%93Noll%E2%80%93Vo_hash_function

[sebastienros]

Should it be lazy or is any Key always checked at least once for equality?

[lahma]

The keys are basically always used against dictionaries, we are trying to find identifiers in context (variables, object fields), we climb up the environment util root (global) and each time pre-calculated hash is being used.

[sebastienros]

A stupid idea you will debunk for sure: Assuming most keys are smallish, can't we use an optimization by using the raw memory value of the strings < 8 chars (64bits -> int) as the hashcode? And then fallback above 8 chars? This way for <8 chars we just need to compare the hashes too, and the computation could be faster (TBD).

[lahma]

Not a stupid idea for sure, makes sense but I'm not an entropy expert (how that would affect collisions).

I also played with the idea of having length < 4 directly interned and then reference equals would suffice in Key context.

I hope to create a new baseline to improve upon, but feels that perf runs can be quite unreliable - results vary a lot...

[lahma]

Jint.Benchmark.DromaeoBenchmark

Diff	Method	Toolchain	FileName	Mean	Error	Allocated
Old	Run	Default	dromaeo-3d-cube	22.934 ms	0.0874 ms	6284.28 KB
New		Default		22.781 ms (-1%)	0.0802 ms	6284.28 KB (0%)
Old	Run	Default	dromaeo-core-eval	4.567 ms	0.0131 ms	311.47 KB
New		Default		4.203 ms (-8%)	0.0106 ms	311.47 KB (0%)
Old	Run	Default	dromaeo-object-array	45.107 ms	0.2320 ms	100362.96 KB
New		Default		44.774 ms (-1%)	0.0921 ms	100362.95 KB (0%)
Old	Run	Default	droma(...)egexp [21]	164.136 ms	1.2785 ms	160554.4 KB
New		Default		161.919 ms (-1%)	1.8212 ms	165388.61 KB (+3%)
Old	Run	Default	droma(...)tring [21]	305.667 ms	8.9598 ms	1321524.27 KB
New		Default		327.253 ms (+7%)	9.7981 ms	1321594.6 KB (0%)
Old	Run	Default	droma(...)ase64 [21]	52.778 ms	0.1894 ms	6045.2 KB
New		Default		47.342 ms (-10%)	0.1317 ms	6045.71 KB (0%)
Old	Run	Default	dromaeo-3d-cube	21.214 ms	0.0316 ms	5994.93 KB
New		Default		20.918 ms (-1%)	0.0508 ms	5994.94 KB (0%)
Old	Run	Default	dromaeo-core-eval	4.246 ms	0.0173 ms	298.91 KB
New		Default		3.938 ms (-7%)	0.0345 ms	298.91 KB (0%)
Old	Run	Default	dromaeo-object-array	45.387 ms	0.1600 ms	100324.03 KB
New		Default		43.991 ms (-3%)	0.2207 ms	100324.05 KB (0%)
Old	Run	Default	droma(...)egexp [21]	155.237 ms	1.6311 ms	163082.43 KB
New		Default		156.562 ms (+1%)	2.4694 ms	168520.57 KB (+3%)
Old	Run	Default	droma(...)tring [21]	316.258 ms	10.3567 ms	1321256.9 KB
New		Default		320.153 ms (+1%)	14.0838 ms	1321238.15 KB (0%)
Old	Run	Default	droma(...)ase64 [21]	50.761 ms	0.1518 ms	5957.75 KB
New		Default		48.152 ms (-5%)	0.1664 ms	5958.38 KB (0%)

[lahma]

Method	Input	Mean	Error	StdDev	Ratio	RatioSD	Rank
Fnv1	encodeURIComponent	8.2694 ns	0.0245 ns	0.0229 ns	0.80	0.00	1
StringHashCode	encodeURIComponent	10.3244 ns	0.0579 ns	0.0513 ns	1.00	0.00	2
StringOrdinalHashCode	encodeURIComponent	10.7936 ns	0.1451 ns	0.1357 ns	1.04	0.01	3
Hash3	encodeURIComponent	13.9756 ns	0.0278 ns	0.0260 ns	1.35	0.01	4
Fnv1	i	0.1548 ns	0.0030 ns	0.0028 ns	0.09	0.00	1
StringHashCode	i	1.6543 ns	0.0003 ns	0.0003 ns	1.00	0.00	2
StringOrdinalHashCode	i	1.9382 ns	0.0093 ns	0.0083 ns	1.17	0.00	3
Hash3	i	9.7149 ns	0.0242 ns	0.0227 ns	5.87	0.01	4
Fnv1	Math	1.2434 ns	0.0055 ns	0.0051 ns	0.39	0.00	1
StringHashCode	Math	3.1640 ns	0.0005 ns	0.0005 ns	1.00	0.00	2
StringOrdinalHashCode	Math	3.3992 ns	0.0093 ns	0.0087 ns	1.07	0.00	3
Hash3	Math	9.9248 ns	0.0015 ns	0.0014 ns	3.14	0.00	4
Fnv1	str	0.5622 ns	0.0058 ns	0.0054 ns	0.23	0.00	1
StringHashCode	str	2.4333 ns	0.0080 ns	0.0075 ns	1.00	0.00	2
StringOrdinalHashCode	str	2.4922 ns	0.0073 ns	0.0068 ns	1.02	0.00	3
Hash3	str	9.7433 ns	0.0375 ns	0.0351 ns	4.00	0.02	4