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digitalmars.D.learn - BitArray Slicing

reply Ezneh <petitv.isat gmail.com> writes:
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.
Dec 21 2016
next sibling parent reply Eugene Wissner <belka caraus.de> writes:
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.
Dec 21 2016
parent Ezneh <petitv.isat gmail.com> writes:
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.
Dec 21 2016
prev sibling parent reply Ilya Yaroshenko <ilyayaroshenko gmail.com> writes:
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
}
------
Dec 21 2016
parent reply Ezneh <petitv.isat gmail.com> writes:
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
Dec 21 2016
parent Ilya Yaroshenko <ilyayaroshenko gmail.com> writes:
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).
Dec 21 2016