Tiny Lua Distribution 5.1.4

Lua 5.1.4 is out so I recompiled it with Dev-C++ to make the windows version a standalone EXE. Strangely enough, it became some KB larger than 5.1.3. Anyway here is the new Tiny Lua Distribution. (contains Linux and Windows interpreters)

Big table implementation in Brainfuck

In the past I had found an efficient way of implementing tables on the Brainfuck array. There were already some table implementations which used at least 2*n Brainfuck cells for storing an n sized table. My implementation needed only n+4.

Also, all known implementations had a limit of 256 cells (Or equal to the size of a cell on the Brainfuck array. For the rest of the post I will assume that the cell size is one byte).

During my road-trip to Spain, based on my old implementation, I found a new one that can use multiple indexes to implement tables of ANY size on the Brainfuck array. Additionally the table cell size can be any multiple of the Brainfuck array's cell size.

It uses a format similar to my old implementation: a head moving through the table while decreasing the index it carries, passing table data over it, until it finds the correct position,the it does it's job (read/write) and then it returns in the same way but using a copy of the index.

For a table with n cells of size k each the form of the header is:

• k empty cells: When the head need's to move to the right, it will have to move the first k cells on it's right in these empty cells before moving itself k positions to the right (thus moving itself to the next indexed position)
• n index cells: Before starting a read or write operation you will have to store the index here. The leftmost index is the most important. For example if the maximum possible value for an index is 9 (instead of 255) and you use two indexes, to access the 15th cell you would have to use 1 for the left index and 4 for the right index (not 5 because the numbering starts from 0).
• k data cells: To write to the table you will have to put the data in these cells. If you read from the table, after the end of the read operation the read data will be here. These cells MUST be cleared before starting a read operation.
• n empty (index) cells: While the index cells are reduced, these cells are increased so that, when the seek operation finishes, they will hold a copy of the original indexes which will be used for returning the head to the beginning of the table.

After the header the table data is assumed to be laying. n*k cells in total. For example for a size 400 table with 2 bytes per cell they would have this form:
Data 1 of index 0,0
Data 2 of index 0,0
...
Data 1 of index 0,255
Data 2 of index 0,255
Data 1 of index 1,0
Data 2 of index 2,0
Data 1 of index 1,1
Data 2 of index 2,1
...
...
Data 1 of index 1,143
Data 2 of index 1,143

So you will need 2*k+2*ceil(log256(n))+n*k cells on the Brainfuck array to store a table with n, k-sized cells. (ceil(log256(n)) is the number of the indexes)

Therefore the code needed to write or read from the table depends on n and k. I actually wrote some metacode that provided with n and k produces the corresponding code. I then turned the metacode into a Lua script. It's not well written but I believe that it works. I tried the following cases:

1. Writing two values to a table with n<256 and k=1 and then reading them back.
2. Writing two values to a table with 256<n<256^2 and k=2 and then reading them back.

and everything worked fine.

If you want to try the script yourself you download it from here.

Here is some example code:

n<256 k=1
Write:
>[->>+>[-<<<<+>>>>]<[->+<]<[->+<]
<[->+<]>]>>>[-]<<[->>+<<]>[-[-<+>
]<<<<[->>>>+<<<<]>>>]<<<
Read:
>[->>+>[-<<<<+>>>>]<[->+<]<<[->+<
]>]>>>[-<<+<<+>>>>]<<<<[->>>>+<<<
<]>>>[-<[-<+>]>[-<+>]<<<<[->>>>+<
<<<]>>>]<<<

256<n<256^2 k=1
Write:
>>[->>>+>[-<<<<<<+>>>>>>]<[->+<]<
[->+<]<[->+<]<[->+<]<[->+<]>>]<[-
>>>+>>[-<<<<<<+>>>>>>]<[->+<]<[->
+<]<[->+<]<[->+<]<[->+<]>>-[->>>>
[-<<<<<<+>>>>>>]<[->+<]<[->+<]<[-
>+<]<[->+<]<[->+<]>>]<]>>>>>[-]<<
<[->>>+<<<]>>[-<[-<+>]>[-<+>]<<<<
<<[->>>>>>+<<<<<<]>>>>>]<[-[-<+>]
>[-<+>]<<<<<<[->>>>>>+<<<<<<]>>>>
>-[-<[-<+>]>[-<+>]<<<<<<[->>>>>>+
<<<<<<]>>>>>]<]<<<<
Read:
>>[->>>+>[-<<<<<<+>>>>>>]<[->+<]<
[->+<]<<[->+<]<[->+<]>>]<[->>>+>>
[-<<<<<<+>>>>>>]<[->+<]<[->+<]<<[
->+<]<[->+<]>>-[->>>>[-<<<<<<+>>>
>>>]<[->+<]<[->+<]<<[->+<]<[->+<]
>>]<]>>>>>[-<<<+<<<+>>>>>>]<<<<<<
[->>>>>>+<<<<<<]>>>>>[-<<[-<+>]>[
-<+>]>[-<+>]<<<<<<[->>>>>>+<<<<<<
]>>>>>]<[-<[-<+>]>[-<+>]>[-<+>]<<
<<<<[->>>>>>+<<<<<<]>>>>>-[-<<[-<
+>]>[-<+>]>[-<+>]<<<<<<[->>>>>>+<
<<<<<]>>>>>]<]<<<<

Windows XP and Vista running on Ubuntu

Here is a new video that I uploaded to YouTube. It's my system running Windows XP and Vista at the same time, virtualized with VirtualBox on Ubuntu. The theme I am using is Ubuntu Satanic Edition (with a different background). You can also see the Desktop Cube that Compiz offers. :-)



Still not switched to Linux? ;-) You won't miss Windows this way...

PS: The FPS aren't that slow as they seem to be on the Video. Also, some horizontal red stripes that appear while rotating the cube are a glich in the capture and don't really exist.

Windows 2.03 on a Virtual Machine

Virtual Machines can be proven very useful tools. I have been using QEmu for some time now but I recently switched to VirtualBox (commercial, but free of charge, edition) because I desperately needed the USB support. Here is a screenshot showing my four desktops while in one of them is a virtual machine running XP in fullscreen mode:


Apart from running a "useful" OS on the virtual machine (it's useful because I needed to use a 3G GPRS USB modem which doesn't work on Linux) you can also run old or rare OSes. I tried Warp but I couldn't install it just like Windows 1.0. So I tried Windows 2.03 which did install and run properly. I also made a video with a quite lengthy tour showing most of their programs. (it's five minutes long!)

Here it is:

Hanoi Towers Solver

I just made a small program that solves, step by step, the Hanoi Towers puzzle for any number of disks. I though it's worth uploading it, so here it is. As always, it's a console application with nice (for my taste) ASCII graphics. It runs on both Linux and Windows as it is written in Lua. I included two Lua interpreters (for both OSes). To run it just drag and drop the .lua file on the interpreter. (after unzipping everything, of course). Here is screenshot: (When giving the number of disks remember that the total moves for the solution are 2^(number of disks)-1. And you will have to press as many Enters as the moves.)