Hello,

First of all, bitset.js is a really useful tool. Thanks for your efforts.

My question is about memory usage of a BitSet. I assume that a BitSet is as large as of its MSB. Let's say we have a BitSet whose 300,000,000th bit is set as 1, remaining are zero. We need to allocate 300M bits, right? If so, total size should be around ~35.7 MB. However, when I execute this scenario (set 300Mth bit as 1), BitSet size is calculated as 194.5 MB. I use an npm package object-sizeof to do that. I naturally don't expect it to allocate exactly 300M bits, instead a close number which is better for memory management. But the difference is huge. So, which is correct? Do I misunderstand something?

Thanks.

I'm working on fixed size bitsets, and I create a 64 bit bitset by doing: new BitSet(new Uint8Arrray(4)).

When calling ntz() on this object, it returns Infinity, IMO it should return the size of the bitmap which in this case is 64.

If the word is zero (no bits set), count leading zeros and count trailing zeros both return the number of bits in the word, while ffs returns zero. Both log base 2 and zero-based implementations of find first set generally return an undefined result for the zero word. https://en.wikipedia.org/wiki/Find_first_set#Algorithms

While ffs is something that could return Infinity.

Hi,

This is a great lib, especially the infinite length feature.

Is it possible to get a published version that is compatible with webpack using ES5 exports?

Many thanks!

For the most part, I like BitSet however, (taking a clue from "Prototype the User Experience"), I think the usability could be increased if you made the following changes:

1. All mathematical operations are immutable operations, which return back a new BitSet object.
2. All other function, those that changes the object, are mutable. (E.g. Set(), SetRange(), Clear(), and (perhaps) Flip()).

The reason for this is simple, I want to change the actual BitSet when I'm performing an operation directly on the object. However, like Math, operations like: 'and', 'or', "not' etc don't change the lhs or the rhs operands; they just return a new result value. Likewise, BitSet should do the same.

I just spent 20 minutes tracking down a very subtle but because I forget to assign the return value from a Set operation to itself.

This code feel very natural: permissions.set(Read) This doesn't feel natural: permissions = permission.set(Read)

Hope that helps.

We have permission data stored as a byte[], can BitSet be initialized with a byte[]? If so, what would the syntax look like? something like: var bs = new BitSet(bitarray);

And if not, how would we implement it?

Do you have a TypeScript Definition file? If not, I have a good start on one.

Also, any plans on porting to TypeScript? If so (or not) my guys are thinking about porting it anyway. If they end up porting it, would you like a pull request?

Thanks for this library! In my testing, it is almost as fast as the one shipped with Java.

I need a way to know how big the bitset is. size() or count() or something like that.

This might be because the forEach() is still lacking, but I am not sure

Does this library optimize large ranges of the same value?

For example, if 1 million bits are marked true, then 1 million false, then one million true, is this internally represented using ranges to compress the information and optimize lookups?

Can such a format be exported/imported to/from JSON?

Perhaps there is another better suited data structure for this purpose?

Thank you.

1. Use Gulp to build with Closure Compiler Fixed a couple of type warnings from Closure Compiler. Add a section in README.md explaining how to build the library.
2. In toString(), pre-allocate 'arr' instead of growing it. This should improve performance on most JavaScript engines

I might be mis-reading the documentation, but as I understand, the following two objects should be equivalent:

let a = new BitSet([34]).not()
let b = new BitSet().set(34,1).not()

however they are not:

a.get(80)  // returns 0, not what I expected
b.get(80)  // returns 1

In bitset.js, and the .d.ts in #27, the comments for the bitwise operators include "The result is stored in-place".

I see that the Readme.md does show the correct immutable description, but the inline documentation should either be kept up to date, too, or remove it.

affected functions: and, or, andNot, not, xor

I was trying to use this library to push to the client-side a few things that were being done server-side with either Java's BitSet or C#'s BitArray. Unfortunately, I've found some of the results did not match the values I'd expect.

For example, I have a Uint8Array of [ 240, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 127, 255, 31 ,0 ,0]. When I check the toArray() it shows the first 'flipped' bit to be at index 8 (should be 4) and the indices 13, 14, and 15 to be set to 0 with quite a few more down the line that don't match the Java or C# response to the dame byte array.

Hi,

I want to store 214 bits in a BitSet. When i do that it's data array is 10 elements. That's 10x 32bit int (320 bit). Ideally it would use the bare minimum in bit overhead. If that were to be done in 32 bit ints then 7 ints (224 bit) would suffice. More ideal would be an array of chars (8 bit each) where i'd need 27 chars giving me 216 bits of room.

Are there arguments i can set in this class to get that more ideal behavior (ints or chars, both work)?

As we can construct a bitset object by a Buffer, Can we convert the bitset to Buffer

let bitset = require("bitset"); let buf = Buffer.from([100, 97, 98]); let bs = bitset(buf); bs.toString(); '11000100110000101100100'

Can we convert a bitset into buffer? let bs1 = new bitset(); bs1.setRange(4,9,1); { data: [ 1008, 0, 0, 0, 0, 0, 0, 0, 0, 0 ], _: 0 } bs1.toString(); '1111110000'

Now can this be converted into the buffer? eg. add the padding 0's left and make it's size multiple of 8 then convert to byte array or Buffer.

• OS: Windows 10 Pro
• Browser: Internet Explorer 11 (and emulation back through 7 and 5)

Error encountered:

SCRIPT1028: Expected identifier, string or number
bitset.js (911,5)

which points to the following line:

[Symbol.iterator]: function () {

I wasn't familiar with this as valid JS syntax, but some Googling helped me discover it's called a "computed property name" and that IE doesn't support it. I'm aware that IE is largely obsolete with Microsoft's promotion of Edge, but it still exists and does function as a modern browser for the most part. Could you switch to alternate syntax for adding the iterator? Many thanks!

Re #39. I don't know that I got the implementation right, but it works so far with the test cases I've added. I hope you'll consider adding shifts to the library.

I noted that the gulpfile is not compatible with gulp 4, so it might be a good idea to change the gulp dependency to version 3. I didn't include a minified file, as it will of course be an ugly diff, but I did generate one in order to run tests.

All the best, Karl