If the data is completely zero, then count leading zeros and count trailing zeros should return the word size

[CMCDragonkai]

If the data is completely zero, then count leading zeros and count trailing zeros should return the word size

[infusion]

Thanks for the ticket, that makes sense. What I don't get is how you get a 64 bit bitset with 4x8bit. Even if the 8bit array is mapped 1:1 to the internal 31 bit Array structure, it's 4x31=124bit.

[CMCDragonkai]

My understanding is that Uint8Array(4) creates 4 of 8 bit ints. This triggers an extension from 32 bit to 64 bits based on your fixed wordsize of 32 bits. I tested it and it behaved that way.

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On 19 Jun 2017 23:02, "Robert Eisele" ***@***.***> wrote: Thanks for the ticket, that makes sense. What I don't get is how you get a 64 bit bitset with 4*8bit. Even if the 8bit array is mapped 1:1 to the internal 31 bit Array structure, it's 4*31=124bit. — You are receiving this because you authored the thread. Reply to this email directly, view it on GitHub <#21 (comment)>, or mute the thread <https://github.com/notifications/unsubscribe-auth/AAnHHQqoNJlakOOUHDyU4sfnEHmIKgLNks5sFnFmgaJpZM4N-GWw> .

[infusion]

Okay, I see your point now. Even if Bitset.js allocates 64 bits, it doesn't mean it's the actual size. Consider the following:

console.log(new BitSet(new Uint8Array([1,2,3,4])))

which produces: { data: [ 67305985, 0 ] }

That means the whole 4 bytes are packed into the 32bit integer - which makes sense. The additional zero is just a slight extension for performance reasons, since it could happen that one of the proceeding bits is touched soon.

So, I see your point here. Also on the whole topic, that 64 should be returned. But it isn't correct and doesn't make too much sense, since the internal allocated data doesn't represent the external state. And things are getting even more complicated with #22. Since Bitset.js provides arbitrarily large bit vectors, Infinity is the only reasonable answer to ntz(). You bring additional knowledge into play here, since you know JavaScript works on 32bit integers and as such Bitset.js does. But the purpose of this library is to abstract over this limitation.

Could you elaborate on how you want to use ntz with a bit vector of all zeros? What would 64 mean to you in your application?

[CMCDragonkai]

It doesn't matter atm, I wrote an adapter around the bitset functions making it more closer to the API I expected. But checking for Infinity is not any different as checking for ntz = bitmap size in my case.

[infusion]

The thing is, that I don't have the actual bitmap size. I could return arr.length*32, but as I said this doesn't reflect the actual bitmap size, since bitset.js pre-allocates the array with zeros to reduce execution time on stressful environments. I decided to do so, when I fought with Daniel Lemire's fastbitset to win the battle. In a later step I decided to make Bitset.js working with negations - that's where the '_'-attribute was born. This change made Bitset.js an arbitrarily large bit vector implementation, for which ntz=Infty is the most logical answer. That's why I'd like to keep it the way it is.

[CMCDragonkai]

I'm using it for this: https://github.com/MatrixAI/js-resource-counter btw. BitSet is fine currently.

[infusion]

This is a pretty cool use case for Bitset.js! Matrix.ai is a nice project, are u working alone on it?

[CMCDragonkai]

Thanks. Got 1 other team member and 2 other consultants.

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On 26 Jun 2017 7:15 AM, "Robert Eisele" ***@***.***> wrote: This is a pretty cool use case for Bitset.js! Matrix.ai is a nice project, are u working alone on it? — You are receiving this because you authored the thread. Reply to this email directly, view it on GitHub <#21 (comment)>, or mute the thread <https://github.com/notifications/unsubscribe-auth/AAnHHQ25CeO8ShGT0_CIfX9B46n2vkP3ks5sHs4MgaJpZM4N-GWw> .

[infusion]

So, can we close this ticket as well? I mean, Infinity is the only reasonable result and it doesn't make any difference in your code. I added a small note on the ntz doc entry about this behavior.