On Monday, January 22, 2024 7:33:33 PM MST Siarhei Siamashka via Digitalmars-d wrote:
> On Monday, 22 January 2024 at 23:31:16 UTC, deadalnix wrote:
> > On Monday, 22 January 2024 at 22:44:20 UTC, Walter Bright wrote:
> >> On 1/22/2024 1:11 PM, Bruce Carneal wrote:
> >>> Blake3 might be worth a look.  It's reportedly faster and stronger than md5.
> >>>
> >>> https://github.com/BLAKE3-team/BLAKE3
> >>
> >> Thanks for the tip. I don't know how to evaluate a hash function for uniqueness.
> >
> > Blake is > 128 bits, so I don't think there is anything really interesting there anyways.
>
> It's probably possible to take just the first (or last) 128 bits
> of BLAKE3 and the result might have better properties than MD5
> (considering that MD5 is broken). There are some answers related
> to "truncated hash" on the Internet about SHA-256, but any
> cryptographically secure hash is likely to be similar in this
> aspect:
> https://crypto.stackexchange.com/questions/161/should-i-use-the-first-or-las
> t-bits-from-a-sha-256-hash/163#163

Why on earth would we care if the hash is secure in this context? We obviously care about the likelihood of collisions, and if that's high enough (which does not seem to be the case for md5), then the hash is unsuitable for comparing class names, but why would crytographic security matter when comparing class names in the compiler?

- Jonathan M Davis

On Tuesday, 23 January 2024 at 03:34:23 UTC, Jonathan M Davis wrote:
> On Monday, January 22, 2024 7:33:33 PM MST Siarhei Siamashka via Digitalmars-d wrote:
>> On Monday, 22 January 2024 at 23:31:16 UTC, deadalnix wrote:
>> > On Monday, 22 January 2024 at 22:44:20 UTC, Walter Bright wrote:
>> >> On 1/22/2024 1:11 PM, Bruce Carneal wrote:
>> >>> Blake3 might be worth a look.  It's reportedly faster and stronger than md5.
>>
>>
>> It's probably possible to take just the first (or last) 128 bits
>> of BLAKE3 and the result might have better properties than MD5
>> (considering that MD5 is broken). There are some answers related
>> to "truncated hash" on the Internet about SHA-256, but any
>> cryptographically secure hash is likely to be similar in this
>> aspect:
>> https://crypto.stackexchange.com/questions/161/should-i-use-the-first-or-las
>> t-bits-from-a-sha-256-hash/163#163
>
> Why on earth would we care if the hash is secure in this context? We obviously care about the likelihood of collisions, and if that's high enough (which does not seem to be the case for md5), then the hash is unsuitable for comparing class names, but why would crytographic security matter when comparing class names in the compiler?
>
> - Jonathan M Davis

I don't think it matters at all except for what it implies about collisions.  And, again, I don't think any modern hash is bad wrt collisions but I'm not a hash researcher.

If it is true that any modern hash is in the "more likely to be smacked by a meteor than experience a collision" category *and* the current (md5) time burn is more than a blip then it's probably worth taking a look at the alternatives.

OTOH, it's not like there is a shortage of things to work on... :-)

On Monday, 22 January 2024 at 20:46:26 UTC, Walter Bright wrote:
> On 1/22/2024 2:08 AM, Andrea Fontana wrote:
>> Why md5 and not a faster method?
>
> Md5 has an extremely remote chance of two class names hashing to the same value. Some people have argued this is unacceptable, though I opine that the odds are so low they are unimaginable to humans.
>
> A replacement that has a perceptible collision rate will be unacceptable.
>
> This is not a hash backed up by a string compare. The hash has to be a substitute for the string compare.

So probably you like xxhash128

https://xxhash.com/

Andrea

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?

On 1/23/24 2:37 PM, 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?

xxhash has a wiki page about it [1]. Given that it's their page, it's probably unsurprising that xxhash does well.

[1]: https://github.com/Cyan4973/xxHash/wiki/Collision-ratio-comparison#collision-study

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?

Check this:
https://fossies.org/linux/xxHash/tests/collisions/README.md

All good hash algorithms should be uniform...

Andrea