Miscellaneous capabilities of the 16-bit architecture.

§1. Summary. The 16-bit architecture is for very limited virtual machines, and is closely modelled on Infocom's Z-machine, originally developed between 1979 and 1986, but still sometimes used into the modern age. Its input-output model is almost entirely textual, and it has an idiosyncratic character set.

§2. Header layout. The Z-machine contains certain special constants and variables at fixed position in its "header"; the addresses of these are given below. See The Z-Machine Standards Document, version 1.0, for details. 

Constant HDR_ZCODEVERSION     = $00;     byte
Constant HDR_TERPFLAGS        = $01;     byte
Constant HDR_GAMERELEASE      = $02;     word
Constant HDR_HIGHMEMORY       = $04;     word
Constant HDR_INITIALPC        = $06;     word
Constant HDR_DICTIONARY       = $08;     word
Constant HDR_OBJECTS          = $0A;     word
Constant HDR_GLOBALS          = $0C;     word
Constant HDR_STATICMEMORY     = $0E;     word
Constant HDR_GAMEFLAGS        = $10;     word
Constant HDR_GAMESERIAL       = $12;     six ASCII characters
Constant HDR_ABBREVIATIONS    = $18;     word
Constant HDR_FILELENGTH       = $1A;     word
Constant HDR_CHECKSUM         = $1C;     word
Constant HDR_TERPNUMBER       = $1E;     byte
Constant HDR_TERPVERSION      = $1F;     byte
Constant HDR_SCREENHLINES     = $20;     byte
Constant HDR_SCREENWCHARS     = $21;     byte
Constant HDR_SCREENWUNITS     = $22;     word
Constant HDR_SCREENHUNITS     = $24;     word
Constant HDR_FONTWUNITS       = $26;     byte
Constant HDR_FONTHUNITS       = $27;     byte
Constant HDR_ROUTINEOFFSET    = $28;     word
Constant HDR_STRINGOFFSET     = $2A;     word
Constant HDR_BGCOLOUR         = $2C;     byte
Constant HDR_FGCOLOUR         = $2D;     byte
Constant HDR_TERMCHARS        = $2E;     word
Constant HDR_PIXELSTO3        = $30;     word
Constant HDR_TERPSTANDARD     = $32;     two bytes
Constant HDR_ALPHABET         = $34;     word
Constant HDR_EXTENSION        = $36;     word
Constant HDR_UNUSED           = $38;     two words
Constant HDR_INFORMVERSION    = $3C;     four 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;
    return (HDR_GAMERELEASE-->0) & $03ff;
];

[ VM_SerialNumber;
    return HDR_GAMESERIAL;
];

§4. RNG. 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;
    if (n > 0) n = -n;
    @random n -> 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;
    return 0;
];

[ VM_FreeMemory address;
];

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

[ Memcpy to_addr from_addr size  n;
    for (n = size/WORDSIZE: (n--) > 0: ) to_addr-->n = from_addr-->n;
    for (n = size: ((n--) % WORDSIZE ~= 0): ) to_addr->n = from_addr->n;
];

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

[ VM_CopyWords words from to  bytes;
    bytes = words * WORDSIZE;
    @copy_table from to bytes;
];

§8. Audiovisual Resources. The Z-machine only barely supports figures and sound effects, and only in version 6 of the Z-machine, which Inform 7 no longer supports. Sound effects have a longer pedigree and Infocom used them on some version 5 and even some version 3 works: really, though, from an Inform point of view we would prefer that anyone needing figures and sounds use Glulx instead. (Inform 6 remains available for those who really need to make audiovisual effects in these long-gone formats.) 

[ VM_Picture resource_ID;
];

[ VM_SoundEffect resource_ID;
];

§9. Typography. Relatively few typographic effects are available on the Z-machine, so that many of the semantic markups for text which would be distinguishable on Glulx are indistinguishable here. 

[ VM_Style sty;
    switch (sty) {
        NORMAL_VMSTY, NOTE_VMSTY: style roman;
        HEADER_VMSTY, SUBHEADER_VMSTY, ALERT_VMSTY: style bold;
    }
];