Improve the OOP ABI

[Siarhei Siamashka]

On Tuesday, 23 January 2024 at 21:37:42 UTC, Walter Bright wrote:
> On 1/23/2024 3:49 AM, Andrea Fontana wrote:
>> So probably you like xxhash128
>> 
>> https://xxhash.com/
>
> Thanks! I do, it has a 64 bit version, does anyone know what 
> the collision rate is?

If you really need a 64-bit version, then you can simply take the 
first 64 bits of MD5. Assuming no defects in a 64-bit hash 
implementation, the collision probability is `1.0 / 2^^64` for a 
pair of hashed strings. And it becomes a 
https://en.wikipedia.org/wiki/Birthday_problem if the number of 
hashed strings is larger. There's no magic algorithmic sauce that 
can make a small hash collision resistant. A quote from the 
Wikipedia article:

> As an example, if a 64-bit hash is used, there are 
> approximately 1.8×10^^19 different outputs. If these are all 
> equally probable (the best case), then it would take 'only' 
> approximately 5 billion attempts (5.38×10^^9) to generate a 
> collision using brute force.[6] This value is called birthday 
> bound[7] and for n-bit codes it could be approximated as 
> 2^^(n/2).

I would say that any 64-bit hash is not sufficiently collision 
resistant for the problem that you are trying to solve.