Re: Multidimensional Packed Bit Array
- From: "colin" <colin.rowe1@xxxxxxxxxxxxxxxxxx>
- Date: Sat, 29 Dec 2007 12:25:41 GMT
Ive not used it myself but I assume you would just have a BitArray
with enough bits in it to hold all the bits in the entire array.
the amount of memory is just all the dimensions multiplied together.
the offset and multiplier for each dimension is simply the total size of the
lower order dimension.
so for an array a[3,3,3]
would be 27 bits big, a[x,y,z] -> BitArrayStore[x*9+y*3+z]
Colin =^.^=
"Thomas Bruckner" <tbrstore_at_gmail_dot_com> wrote in message
news:%23YPqWwfSIHA.2376@xxxxxxxxxxxxxxxxxxxxxxx
Hello,
I've looked online for an implementation of a multidimensional packed bit
array (like BitArray but with more than one dimension), and could not find
any, so I'm trying to create my own. However with limited success sofar.
I'm having troubles with calculating the required size of the storage and
also with the bit shifts... my brain is turning in circles trying to
figure this out ;-)
Anyone want to help with this?
Thomas Bruckner
using System;
using System.Collections.Generic;
using System.Text;
namespace ConsoleApplication1
{
class Program
{
static void Main(string[] args)
{
// new array 4 dimensions each with 2, 2, 4 and 4 elements
MultiBitArray mba = new MultiBitArray(new int[] { 2, 2, 4,
4 });
for (int i = 0; i <= 3; i++)
{
for (int j = 0; j <= 3; j++)
{
for (int k = 0; k < 15; k++)
{
for (int l = 0; l < 15; l++)
{
int[] coord = new int[] { i, j, k, l};
// make sure it is initially false
System.Diagnostics.Debug.Assert(mba.GetValue(coord) == false);
// set to true, and check
mba.SetValue(coord, true);
System.Diagnostics.Debug.Assert(mba.GetValue(coord) == true);
Console.WriteLine(
mba.GetLocation(coord).ToString());
}
}
}
}
Console.ReadKey();
}
}
public class MultiBitArray
{
/// <summary>
/// Number of dimensions.
/// </summary>
private int dimCount;
/// <summary>
/// bite size of each dimension (may be different)
/// </summary>
private int[] bitSize;
/// <summary>
/// storage for bits
/// </summary>
internal byte[] storage;
public MultiBitArray(int[] bitSize)
{
this.dimCount = bitSize.Length;
this.bitSize = bitSize;
AllocStorage();
}
/// <summary>
/// Allocates storage space for bits.
/// </summary>
private void AllocStorage()
{
long storageSize = 1;
for (int i = 0; i < this.dimCount; i++)
{
storageSize *= (this.bitSize[i] * dimCount);
}
// i can't even figure out how to determine the
// amount of memory... so I set it very large for testing
//storageSize *= 4;
this.storage = new byte[storageSize];
}
/// <summary>
/// Gets the location of a bit according to dimension indexes
/// </summary>
internal int GetLocation(int[] coord)
{
int location = 0;
int bitcount = 0;
for (int i = 0; i < dimCount; i++)
{
location = (location << bitcount) | coord[i];
bitcount = this.bitSize[i];
}
return location;
}
/// <summary>
/// Read a bit.
/// </summary>
public bool GetValue(int[] coord)
{
int location = GetLocation(coord);
return (this.storage[location / 8] & (byte)(1 << (location %
8))) != 0;
}
/// <summary>
/// Set a bit.
/// </summary>
public void SetValue(int[] coord, bool value)
{
int location = GetLocation(coord);
this.storage[location / 8] |= (byte)(1 << (location % 8));
}
}
}
.
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