ibniz

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Original Source: http://pelulamu.net/ibniz/

Compilation in Unix-like systems that have GCC and SDL installed: make

This documentation represents IBNIZ version 1.1 released on 2011-12-27. The distribution licence is the "zlib/libpng licence" (see licence.txt).

=== OVERVIEW ===

IBNIZ is a virtual machine designed for extremely compact low-level audiovisual programs. The leading design goal is usefulness as a platform for demoscene productions, glitch art and similar projects. Mainsteam software engineering aspects are considered totally irrelevant.

IBNIZ stands for Ideally Bare Numeric Impression giZmo. The name also refers to Gottfried Leibniz, the 17th-century polymath who, among all, invented binary arithmetic, built the first four-operation calculating machine, and believed that the world was designed with the principle that a minimal set of rules should yield a maximal diversity.

The IBNIZ virtual machine is basically a two-stack machine somewhat similar to Forth implementations but with the major difference that the stack is cyclical and also used as output buffer. The machine runs in an endless loop by default, with the loop counter variable(s) pushed on top of the stack on every loop cycle.

Each instruction is one character long, with the exception of 'loadimm' which consists of a string of hexadecimal digits. This also gives IBNIZ some flavor of an esoteric programming language.

NOTE: IBNIZ has not been fully defined or implemented yet! Anything mentioned in this document may change (although major changes are unlikely).

=== QUICK TUTORIAL ===

The primary implementation of IBNIZ is interactive. You can edit the code like in a normal text editor, start/pause it with f1 and restart it with f2.

The simplest example program is the empty program; it uses the loop variables directly as pixel values and audio data.

A slightly longer example program would be:

    ^xp

Which consists of three operations: ^ (xor), x (exchange) and p (pop).

In the default video context mode ("TYX-video"), the machine pushes the variables T, Y and X on top of the main stack on every loop cycle.

The first opcode (xor) replaces the two topmost values on the stack (Y and X) with their exclusive OR (Y XOR X).

The next opcode is (exchange) corresponds to Forth's SWAP. It swaps the topmost values on the stack. So, after this operation, T is on top of the stack and Y XOR X is under it.

The last opcode, 'pop' ('p') corresponds to Forth's DROP and moves the stack pointer so that the value on top of the stack gets 'popped off'. So, after the execution of the three instructions '^xp', the values T Y X have been transformed into Y XOR X.

Whatever data remains in the stack is interpreted as pixel colors in the YUV colorspace (bit format VVUU.YYYY; thus, the integer part roughly corresponds to hue and the fraction part to intensity). As the range of X and Y is between -1.0 and +1.0 (FFFF.0000 .. 0000.FFFF), the picture resulting from X XOR Y will have a full intensity range but the only hues are 0000 (pure gray) and FFFF (nearly pure gray). The unit for T, by the way, is 1/60 seconds.

The video stack is two video pages long. The visible page is flipped every time the stack pointer passes a page boundary.

An audio example:

    d3r15&*

In the audio context, only one value (T) is pushed on top of stack on each loop cycle. The first opcode 'd' duplicates it, 3r rotates the duplicate right by three bits, 15& ands it with hex number 15 (decimal 21) and * multiplies the result with the original T.

In the audio context, T has the same rate as in video mode; the integer part increments 60 times per seconds. However, the fraction part is also used (resulting in a theoretical maximum sample rate of nearly 4 MHz). Of the values left on stack, only the fraction part is used. It is interpreted as a 16-bit unsigned linear PCM value. Regardless of the actual sampling rate of the implementation, the audio stack is one second long.

IBNIZ always tries to execute programs simultaneously in video and audio contexts. There are two different modes for the video context: the previously-mentioned TYX-video (which pushes T Y X on every loop as three separate numbers) and T-video (which combines these variables in a single value). IBNIZ automatically detects the correct mode by stack usage.

It is possible to separate video and audio calculation using the 'mediaswitch' opcode ('M'). The execution of these separate program portions is scheduled by VM-level logic: in normal cases, the video context loop is run 64 times per audio context loop cycle.

    *x~FF&* M d3r15&*

IBNIZ is a universal programming language, not just an expression evaluator. The secondary stack (return stack or "rstack") makes it possible to implement advanced program control features such as loops, subroutines and recursion. It is also possible to ignore the exterior loop altogether and write to the buffers like to any random access memory as well as to read user input and to have a separate data segment for any arbitrary data.

=== TECHNICAL NUMBERS** ===

Technical specs of the default configuration:

Word width: 32 bits (arithmetic in 16.16 fixed-point) Address space: 2^20 words (4 megabytes, ~3 of which free user RAM) Video output: 256x256 pixels at 60 Hz, 32 bits per pixel (VVUU.YYYY) Audio output: 61440 Hz mono (30720 Hz stereo), 16 bits per sample Computation speed: not defined yet (fully depends on underlying hardware)

=== FULL INSTRUCTION SET ===

Everything is case-sensitive here!

NUMBERS

    symbol  name    stack
    ------  ----    -----
    0-F.    loadimm (-- val)

    The basic numeric type is the 32-bit fixed-point number, divided
    into 16 bits of integer and 16 bits of fraction.

    The number format in the source code is upper-case hexadecimal using
    the digits 0-9 and A-F. The separator '.' can be used to separate
    the fraction part from the integer part.

    Several immediate numbers can be separated with a blank or comma
    (',').

ARITHMETIC

    symbol  name    stack
    ------  ----    -----
    +       add     (a b -- a+b)
    -       sub     (a b -- a-b)
    *       mul     (a b -- a*b)
    /       div     (a b -- a/b, 0 if b==0)
    %       mod     (a b -- a MOD b, 0 if b==0)
    q       sqrt    (a -- square root of a; 0 if a<0)

    &       and     (a b -- a AND b)
    |       or      (a b -- a OR b)
    ^       xor     (a b -- a XOR b)
    r       right   (a b -- a ROR b)
    l       left    (a b -- a << b)
    ~       neg     (a -- NOT a)

    s       sin     (a -- sin(a*2PI))
    a       atan    (a b -- atan2(a,b)/2PI)

    <       isneg   (a -- a if a<0, else 0)
    >       ispos   (a -- a if a>0, else 0)
    =       iszero  (a -- 1 if a==0, else 0)

    All numbers used in arithmetic are interpreted as signed 16+16-bit
    fixed-point values (negative numbers in two's complement).

    The modulus (%) uses fractions.

STACK MANIPULATION

    symbol  name            stack            description
    ------  ----            -----            ----------
    d       dup             (a -- a a)
    p       pop             (a --)           same as Forth's DROP
    x       exchange        (a b -- b a)     same as Forth's SWAP
    v       trirot          (a b c -- b c a) same as Forth's ROT
    )       pick            (i -- val)       load value from STACK[top-1-i]
    (       bury            (val i --)       store value to STACK[top-2-i]

    The operations 'pick' and 'bury' and 'movesp' are always wrapped
    within the stack range.

    The symbol 'v' was chosen because it resembles a triangle.

EXTERIOR LOOP

    symbol  name            description
    ------  ----            -----------
    M       mediaswitch     switches between audio and video context
    w       whereami        pushes exterior loop variable(s) on stack
    T       terminate       stops program execution

    The execution starts in the video context. When the execution wraps
    from the end of the program to the beginning, the VM implicitly
    executes 'mediaswitch' and 'whereami'.

    The loop variables pushed by 'whereami' depend on the stack pointer
    and internal video/audio frame counters. The exact operation,
    depending on context and mode, is as follows:

    context  mode  pushes on stack
    -------  ----  ---------------
    video    TYX   TTTT.0000, YYYY.YYYY, XXXX.XXXX
                   where
                   - YYYY.YYYY and XXXX.XXXX are between -1 and +1
                     (FFFF.0000 and 0000.FFFF)
                   - TTTT is the frame counter (time in 60ths of second)

    video    T     TTTT.YYXX
                   where
                   - TTTT is the frame counter
                   - YY and XX range from 00 to FF (directly from SP)

    audio    T     TTTT.TTTT
                   where
                   - the integer is the frame counter (same as in video)
                   - the fraction is, well, the 65536th part thereof

    The current implementation changes the video context mode
    automatically based on stack balance and how many times 'whereami'
    is called.

MEMORY MANIPULATION

    symbol  name    stack
    ------  ----    -----
    @       load    (addr -- val)
    !       store   (val addr --)

    All the memory is addressed in 32-bit-wide chunks. There is no
    byte-level operation.

    The fractional part of the memory address is interpreted as the high
    part of the logical address. (e.g. 1234.FFFF refers to the address
    FFFF1234).

    In the default configuration, the top 12 bits of the address are
    ignored (thus, the actual address in the previous example is F1234). 
    The total address space is therefore 1 megaword == 4 megabytes. It
    is divided as follows:

    00000 - BFFFF   free for user data
    C0000 - C7FFF   reserved for internal registers, code, etc.
    C8000 - CBFFF   return stack for audio context
    CC000 - CFFFF   return stack for video context
    D0000 - DFFFF   audio stack
    E0000 - EFFFF   video stack page 0
    F0000 - FFFFF   video stack page 1

PROGRAM CONTROL

Conditional execution

    symbol  name    description
    ------  ----    -----------
    ?       if      (cond --) ; if cond==0, skip until 'else' or 'endif'
    :       else    skip until after next 'endif'
    ;       endif   nop; marks end of conditional block when skipping

    End of code is also regarded as a skip terminator in all cases.

Loops

    symbol  name    description
    ------  ----    -----------
    X       times   (i0 --) loop i0 times (push i0 and insptr on rstack)
    L       loop            decrement RSTACK[top-1], jump back if non-0
    i       index	(-- i)  load value from RSTACK[top-1]
    j       outdex	(-- j)  load value from RSTACK[top-3]
    [       do              begin loop (push insptr on rstack)
    ]       while (cond --) jump back if cond!=0
    J       jump    (v --)  set instruction pointer to value v

    Examples of loop constructs:

    100X 3i@L       stores the number '3' to addresses 1..100
    [1r dA0-<]      shifts number right until it is below A0

    The jump instruction (like all ops that manipulate instruction
    pointer directly) wraps around the code length (it is not possible
    to jump outside the program space). As the internal encoding of
    programs has not been defined yet, the exact addresses of the
    instructions are implementation-dependent.

    The times-loop counters (i and j) are regarded as 32-bit unsigned
    integers in the same way as memory addresses (.0001 = 10000). Thus,
    times-loops with more than 65535 steps are possible.

Subroutines

    symbol  name    stack   description
    ------  ----    -----   -----------
    {       defsub  (i --)  define subroutine (store pointer to MEM[i])
    }       return          end of subroutine; pop insptr from rstack
    V       visit   (i --)  visit subroutine pointed to by MEM[i]

    The return stack is used for storing the return addresses when
    visiting subroutines.

    Defsub ('{') stores the address of the next instruction to the
    memory address given by the value on top of stack and then skips
    instructions until '}' or end-of-code is reached.

Return stack manipulation

    symbol	name    stack      rstack       description
    ------	----    -----      ------       -----------
    R       retaddr (-- val)   (val --)     moves from stack to rstack
    P       pushtors (val --)  (-- val)     moves from rstack to stack

    The return stack is cyclical just like the main stack.

INPUT

    symbol  name    stack           description
    ------  ----    -----           ------------
    U       userin  (-- inword)     get data from input device

    The 'userin' instruction polls data from the input device.
    It returns a word in the format MMKK.YYXX where:
    - YYXX indicates the last known position, in unsigned coordinates,
      of the pointing device (mouse, touch, lightpen, etc.)
    - KK indicates the unicode number of the last character entered on
      keyboard, or 0 if no character is entered. If the unicode number
      is above FF, it is wrapped to between 00 and FF. The value is
      cleared to zero (or the next character in the buffer) whenever 'U'
      is used.
    - MM is a bit structure indicating the state of click/state and a
      couple of keyboard keys. Bits from top to bottom:
      80: click state (1 when a screen position is being clicked/touched)
      40: ctrl key (1 = down)
      20: alt/meta key
      10: shift key
      08: cursor up key
      04: cursor down key
      02: cursor left key
      01: cursor right key

DATA SEGMENT

    symbol  name            description
    ------  ----            -----------
    G       getdata         (numbits -- data)
    $       startdata       end code segment, start data segment

    A "data segment" containing arbitrary binary data can be defined
    after the program code. Startdata ($) ends the code segment and
    starts the data segment.

    When a program is started, the memory is filled with the contents of
    the data segment without any alignment.

    Getdata ('G') can be used for reading the data segment sequentially.
    It fetches the given number of next bits from the data segment. When
    it runs out of data, it wraps back to the beginning.

    In the source code, the data is encoded as digits that represent 1-4
    bits in the memory. The following symbols are available:

    symbol	name            description
    ------	----            -----------
    0-F     data            encodes a digitful (1-4 bits) of data.
b       binary	        sets digit length to 1 bit
    q       quarternary     sets digit length to 2 bits
    o       octal           sets digit length to 3 bits
    h       hexadecimal     sets digit length to 4 bits (default)

META

    symbol  name    desc
    ------  ----    ----
    \       comment ignore characters in source code until newline
    ,       blank   nop; also whitespaces and newlines count as blank

=== PRIMARY IMPLEMENTATION ===

EDITOR COMMANDS

    Tab toggles the editor display on/off. When the editor is hidden,
    keyboard commands don't affect the editor state.

    Cursor keys etc. work as expected. Shift+cursor selects an area.

    Ctrl+up/down increments/decrements the number under cursor, with
    carry.

    Ctrl+left/right jumps to the final character of the previous or next
    "word" (i.e. blank-separated section).

    f1 runs and pauses the code.

    f2 resets the VM state (including timer and memory).

    Changes to the source code automatically recompile it but do not
    restart it. This makes it convenient to do runtime changes to
    numeric parameters etc. This functionality may change in the future.

    ESC exits the program.

    Ctrl+C/X/V/A work as copy/cut/paste/selectall.

    Ctrl+S saves the program to the file indicated by a line beginning
    with '\#file' (or if there's no such line, inserts the line
    '\#file untitled.ib' and uses untitled.ib as the filename.
    The '\#file' lines are automatically skipped when saving.

COMMAND LINE OPTIONS

   -h       Dump help on command line usage
   -v       Dump version info
   -c CODE  Execute code
   -n       No autorun of loaded code

   The following extra options were added for creating the YouTube
   video:

   -e       Dump user keystrokes to stdout
   -p       Playback dumped user keystrokes from stdin
   -M       Dump raw video to stdout and raw audio to stderr.
            30 fps, non-realtime, yuv4mpeg2 and pcm_s16.

   Some commands used in this process, for reference:

   ./ibniz -e > events

   ./ibniz -M -p < events 2>vid.pcm | ffmpeg -y -i - -r 30 vid.avi

   ffmpeg -i vid.avi -f s16le -ar 44100 -ac 1 \
   -i vid.pcm -vcodec copy vidav.avi

=== CHANGES ===

1.1:

• Cut/copy/paste implemented, with system clipboard support on X11 and W32.
• VM no longer eats up all CPU time if less is enough for 60 fps.
• Possibility to hide on-screen display (with autohide on autorun)
• Scrolling and buffer size limit check in the editor
• More examples included in the distribution package
• Help screen implemented

=== FUTURE ===

In an approximate order of priority:

• Fix problems that prevent IBNIZ from working in some systems
• Fix other known bugs
• On-screen machine status info
• Improve execution speed with static code analysis and native compilation
• Support resolution reduction etc for slow code/machines
• Remove MSVC library dependency from Win32 build
• Make it possible to limit execution speed
• Make internal registers user-accessible
• Implement IBNIZ as a website
• Native Win32 version (without MVVC library or the statically linked SDL)
• Define and implement a compact bitwise machine code
• Allow self-modifying code
• Support threading, shaders etc.
• Native version for MS-DOS, ibniz-to-c64 compiler etc.

Once we have all of these, we may call the version number 2.0.