Hi, in one of my projects I have to get a slice from a BitArray.

I am trying to achieve that like this :

void foo(BitArray ba)
{
   auto slice = ba[0..3]; // Assuming it has more than 4 elements
}

The problem is that I get an error :

"no operator [] overload for type BitArray".

Is there any other way to get a slice from a BitArray ?

Thanks,
Ezneh.

On Wednesday, 21 December 2016 at 09:08:51 UTC, Ezneh wrote:
> Hi, in one of my projects I have to get a slice from a BitArray.
>
> I am trying to achieve that like this :
>
> void foo(BitArray ba)
> {
>    auto slice = ba[0..3]; // Assuming it has more than 4 elements
> }
>
> The problem is that I get an error :
>
> "no operator [] overload for type BitArray".
>
> Is there any other way to get a slice from a BitArray ?
>
> Thanks,
> Ezneh.

The problem is BitArray keeps multiple elements in one byte. You can't return just three bits but in the best case one byte with 8 elements.

What could be done some internal range could be returned that gives access to the bits. But it isn't implemented.

On Wednesday, 21 December 2016 at 09:14:04 UTC, Eugene Wissner wrote:

>
> The problem is BitArray keeps multiple elements in one byte. You can't return just three bits but in the best case one byte with 8 elements.
>
> What could be done some internal range could be returned that gives access to the bits. But it isn't implemented.

I see, so I have to find another way to get only the range I want from a BitArray.

On Wednesday, 21 December 2016 at 09:08:51 UTC, Ezneh wrote:
> Hi, in one of my projects I have to get a slice from a BitArray.
>
> I am trying to achieve that like this :
>
> void foo(BitArray ba)
> {
>    auto slice = ba[0..3]; // Assuming it has more than 4 elements
> }
>
> The problem is that I get an error :
>
> "no operator [] overload for type BitArray".
>
> Is there any other way to get a slice from a BitArray ?
>
> Thanks,
> Ezneh.

Mir allows you to define simple alternative to BitArray:

https://github.com/libmir/mir

------
struct BitMap
{
    size_t* ptr;

    import core.bitop;

    bool opIndex(size_t index) const
    {
        return bt(ptr, index) != 0;
    }

    void opIndexAssign(bool val, size_t index)
    {
        if(val)
            bts(ptr, index);
        else
            btr(ptr, index);
    }
}

import mir.ndslice;

void main()
{
    auto arr = new size_t[3];
    auto sl = BitMap(arr.ptr).sliced(size_t.sizeof * 8 * arr.length);

    sl[4] = true;
    sl[100] = true;
    sl.popFrontN(3);
    assert(sl[1]);
    assert(sl[97]);

    auto sl2 = sl[1...3]; // slicing
}
------

On Wednesday, 21 December 2016 at 11:49:06 UTC, Ilya Yaroshenko wrote:
> On Wednesday, 21 December 2016 at 09:08:51 UTC, Ezneh wrote:
>> Hi, in one of my projects I have to get a slice from a BitArray.
>>
>> I am trying to achieve that like this :
>>
>> void foo(BitArray ba)
>> {
>>    auto slice = ba[0..3]; // Assuming it has more than 4 elements
>> }
>>
>> The problem is that I get an error :
>>
>> "no operator [] overload for type BitArray".
>>
>> Is there any other way to get a slice from a BitArray ?
>>
>> Thanks,
>> Ezneh.
>
> Mir allows you to define simple alternative to BitArray:
>
> https://github.com/libmir/mir
>
> ------
> struct BitMap
> {
>     size_t* ptr;
>
>     import core.bitop;
>
>     bool opIndex(size_t index) const
>     {
>         return bt(ptr, index) != 0;
>     }
>
>     void opIndexAssign(bool val, size_t index)
>     {
>         if(val)
>             bts(ptr, index);
>         else
>             btr(ptr, index);
>     }
> }
>
> import mir.ndslice;
>
> void main()
> {
>     auto arr = new size_t[3];
>     auto sl = BitMap(arr.ptr).sliced(size_t.sizeof * 8 * arr.length);
>
>     sl[4] = true;
>     sl[100] = true;
>     sl.popFrontN(3);
>     assert(sl[1]);
>     assert(sl[97]);
>
>     auto sl2 = sl[1...3]; // slicing
> }
> ------

Thanks, I'll check that solution to see if it fits my needs.

As an off-topic question, is there any plan in Mir to implement the Tiny Mersenne Twister[1] algorithm (or a wrapper for it) ?

[1] http://www.math.sci.hiroshima-u.ac.jp/~m-mat/MT/TINYMT/index.html

On Wednesday, 21 December 2016 at 12:00:57 UTC, Ezneh wrote:
> On Wednesday, 21 December 2016 at 11:49:06 UTC, Ilya Yaroshenko wrote:
>> [...]
>
> Thanks, I'll check that solution to see if it fits my needs.
>
> As an off-topic question, is there any plan in Mir to implement the Tiny Mersenne Twister[1] algorithm (or a wrapper for it) ?
>
> [1] http://www.math.sci.hiroshima-u.ac.jp/~m-mat/MT/TINYMT/index.html

You are the first who is interested TINYMT, feel free to open a PR in Mir Random

https://github.com/libmir/mir-random

TINYMT should not be big, only Engine itself is required (without floating point stuff and arrays generators).