Miscellaneous capabilities of the 32-bit architecture.

§1. Summary. The 32-bit architecture is currently the default targeted by Inform, and is used both for programs compiled via Inform 6 to the Glulx virtual machine, and also for programs compiled via C.

§2. Header layout. The VM is expected to contain certain special constants and variables at fixed position in its "header"; the addresses of these are given below. 

Constant HDR_MAGICNUMBER      = $00;     long word
Constant HDR_GLULXVERSION     = $04;     long word
Constant HDR_RAMSTART         = $08;     long word
Constant HDR_EXTSTART         = $0C;     long word
Constant HDR_ENDMEM           = $10;     long word
Constant HDR_STACKSIZE        = $14;     long word
Constant HDR_STARTFUNC        = $18;     long word
Constant HDR_DECODINGTBL      = $1C;     long word
Constant HDR_CHECKSUM         = $20;     long word
Constant ROM_INFO             = $24;     four ASCII characters
Constant ROM_MEMORYLAYOUT     = $28;     long word
Constant ROM_INFORMVERSION    = $2C;     four ASCII characters
Constant ROM_COMPVERSION      = $30;     four ASCII characters
Constant ROM_GAMERELEASE      = $34;     short word
Constant ROM_GAMESERIAL       = $36;     six ASCII characters

§3. Release Number. Our programs will have both a release number and a serial code, which are in each case stored in the header memory of the virtual machine.

VM_Describe_Release() has been removed and replaced with functions returning the release number, a non-negative integer, and the serial code, a byte array expected to be 6 digit characters wide. 

[ VM_ReleaseNumber r;
    @aloads ROM_GAMERELEASE 0 r;
    return r;
];

[ VM_SerialNumber;
    return ROM_GAMESERIAL;
];

§4. Random Number Generator. No routine is needed for extracting a random number, since I6's built-in random function does that, but it's useful to abstract the process of seeding the RNG so that it produces a repeatable sequence of "random" numbers from here on: the necessary opcodes are different for the two VMs. 

[ VM_Seed_RNG n;
    @setrandom n;
];

§5. Memory Allocation. This is dynamic memory allocation: something which is never practicable in the Z-machine, because the whole address range is already claimed, but which is viable on recent revisions of Glulx. 

[ VM_AllocateMemory amount i;
    @gestalt 7 0 i;
    if (i == 0) return i;
    @malloc amount i;
    return i;
];

[ VM_FreeMemory address i;
    @gestalt 7 0 i;
    if (i == 0) return;
    @mfree address;
];

§6. Memcpy. This is equivalent to C's memcpy function, in good ways and bad. 

[ Memcpy to_addr from_addr size;
    @mcopy size from_addr to_addr;
];

§7. And this can be used to copy exactly words words from one word array to another: 

[ VM_CopyWords words from to  i;
    for (i=0: i<words: i++)
        to-->i = from-->i;
];

§8. Audiovisual Resources. The Z-machine only barely supports figures and sound effects, so Glulx is the preferred VM to choose if they are wanted. Properly speaking, it's not Glulx which supports these, but its I/O layer Glk, and implementations of Glk are free to support them or not as they please: "cheapglk", a dumb terminal version, does not, for instance. We therefore have to investigate the "gestalt" to find out. 

[ VM_Picture resource_ID;
    if (glk_gestalt(gestalt_Graphics, 0)) {
        glk_image_draw(gg_mainwin, resource_ID, imagealign_InlineCenter, 0);
    } else {
        print "[Picture number ", resource_ID, " here.]^";
    }
];

[ VM_SoundEffect resource_ID;
    if (glk_gestalt(gestalt_Sound, 0)) {
        glk_schannel_play(gg_foregroundchan, resource_ID);
    } else {
        print "[Sound effect number ", resource_ID, " here.]^";
    }
];

§9. Typography. Glk makes an attempt to present typographic styles as being a matter of semantic markup rather than controlling the actual appearance of text: the idea is that the story file should want to print something in a heading kind of way, and then the interpreter — guided by the player's reading preferences — might set that in bold, or larger type, or red ink, or any combination of the three, or with other effects entirely. (This is not the place to discuss whether that was a wise decision for Glk to take.) 

[ VM_Style sty;
    switch (sty) {
        NORMAL_VMSTY:     glk_set_style(style_Normal);
        HEADER_VMSTY:     glk_set_style(style_Header);
        SUBHEADER_VMSTY:  glk_set_style(style_Subheader);
        NOTE_VMSTY:       glk_set_style(style_Note);
        ALERT_VMSTY:      glk_set_style(style_Alert);
        BLOCKQUOTE_VMSTY: glk_set_style(style_BlockQuote);
        INPUT_VMSTY:      glk_set_style(style_Input);
    }
];