Difference between revisions of "SCI/Specifications/SCI virtual machine/The Sierra PMachine"

Certain instructions (in particular, branching ones) take relative addresses as a parameter. The actual address is calculated based on the instruction after the branching instruction itself. In this example, the <tt>bnt</tt> instruction, if the branch is made, jumps over the <tt>ldi</tt> instruction.

Certain instructions (in particular, branching ones) take relative addresses as a parameter. The actual address is calculated based on the instruction after the branching instruction itself. In this example, the <tt>bnt</tt> instruction, if the branch is made, jumps over the <tt>ldi</tt> instruction.

     eq?

     eq?

     bnt +2

     bnt +2

In every call instruction, a value is included which determines the size of the parameter list, as an offset into the stack. This value discounts the list size pushed by the SCI code. For instance, consider this example from real SCI code:

In every call instruction, a value is included which determines the size of the parameter list, as an offset into the stack. This value discounts the list size pushed by the SCI code. For instance, consider this example from real SCI code:

     pushi 3 ; three parameters passed

     pushi 3 ; three parameters passed

     pushi 4 ; the screen flag

     pushi 4 ; the screen flag

pop(): sp -= 2; return *sp;

pop(): sp -= 2; return *sp;

push(x): *sp = x; sp += 2; return x;

push(x): *sp = x; sp += 2; return x;

;<nowiki>op 0x01: bnot (1 byte)</nowiki>

;<nowiki>op 0x01: bnot (1 byte)</nowiki>

:Binary not

:Binary not

acc ^= 0xffff;

acc ^= 0xffff;

</source>

</source>

;<nowiki>op 0x03: add (1 byte)</nowiki>

;<nowiki>op 0x03: add (1 byte)</nowiki>

:Addition:

:Addition:

acc += pop();

acc += pop();

</source>

</source>

;<nowiki>op 0x05: sub (1 byte)</nowiki>

;<nowiki>op 0x05: sub (1 byte)</nowiki>

:Subtraction:

:Subtraction:

acc = pop() - acc;

acc = pop() - acc;

</source>

</source>

;<nowiki>op 0x07: mul (1 byte)</nowiki>

;<nowiki>op 0x07: mul (1 byte)</nowiki>

:Multiplication:

:Multiplication:

acc *= pop();

acc *= pop();

</source>

</source>

;<nowiki>op 0x09: div (1 byte)</nowiki>

;<nowiki>op 0x09: div (1 byte)</nowiki>

:Division:

:Division:

acc = pop() / acc;

acc = pop() / acc;

</source>

</source>

;<nowiki>op 0x0b: mod (1 byte)</nowiki>

;<nowiki>op 0x0b: mod (1 byte)</nowiki>

:Modulo:

:Modulo:

acc = pop() % acc;

acc = pop() % acc;

</source>

</source>

;<nowiki>op 0x0d: shr (1 byte)</nowiki>

;<nowiki>op 0x0d: shr (1 byte)</nowiki>

:Shift Right logical:

:Shift Right logical:

acc = pop() >> acc;

acc = pop() >> acc;

</source>

</source>

;<nowiki>op 0x0f: shl (1 byte)</nowiki>

;<nowiki>op 0x0f: shl (1 byte)</nowiki>

:Shift Left logical:

:Shift Left logical:

acc = pop() << acc;

acc = pop() << acc;

</source>

</source>

;<nowiki>op 0x11: xor (1 byte)</nowiki>

;<nowiki>op 0x11: xor (1 byte)</nowiki>

:Exclusive or:

:Exclusive or:

acc ^= pop();

acc ^= pop();

</source>

</source>

;<nowiki>op 0x13: and (1 byte)</nowiki>

;<nowiki>op 0x13: and (1 byte)</nowiki>

:Logical and:

:Logical and:

acc &= pop();

acc &= pop();

</source>

</source>

;<nowiki>op 0x15: or (1 byte)</nowiki>

;<nowiki>op 0x15: or (1 byte)</nowiki>

:Logical or:

:Logical or:

acc |= pop();

acc |= pop();

</source>

</source>

;<nowiki>op 0x17: neg (1 byte)</nowiki>

;<nowiki>op 0x17: neg (1 byte)</nowiki>

:Sign negation:

:Sign negation:

acc = -acc;

acc = -acc;

</source>

</source>

;<nowiki>op 0x19: not (1 byte)</nowiki>

;<nowiki>op 0x19: not (1 byte)</nowiki>

:Boolean not:

:Boolean not:

acc = !acc;

acc = !acc;

</source>

</source>

;<nowiki>op 0x1b: eq? (1 byte)</nowiki>

;<nowiki>op 0x1b: eq? (1 byte)</nowiki>

:Equals?:

:Equals?:

prev = acc;

prev = acc;

acc = (acc == pop());

acc = (acc == pop());

;<nowiki>op 0x1d: ne? (1 byte)</nowiki>

;<nowiki>op 0x1d: ne? (1 byte)</nowiki>

:Is not equal to?

:Is not equal to?

prev = acc;

prev = acc;

acc = !(acc == pop());

acc = !(acc == pop());

;<nowiki>op 0x1f: gt? (1 byte)</nowiki>

;<nowiki>op 0x1f: gt? (1 byte)</nowiki>

:Greater than?

:Greater than?

prev = acc;

prev = acc;

acc = (pop() > acc);

acc = (pop() > acc);

;<nowiki>op 0x21: ge? (1 byte)</nowiki>

;<nowiki>op 0x21: ge? (1 byte)</nowiki>

:Greater than or equal to?

:Greater than or equal to?

prev = acc;

prev = acc;

acc = (pop() >= acc);

acc = (pop() >= acc);

;<nowiki>op 0x23: lt? (1 byte)</nowiki>

;<nowiki>op 0x23: lt? (1 byte)</nowiki>

:Less than?

:Less than?

prev = acc;

prev = acc;

acc = (pop() < acc);

acc = (pop() < acc);

;<nowiki>op 0x25: le? (1 byte)</nowiki>

;<nowiki>op 0x25: le? (1 byte)</nowiki>

:Less than or equal to?

:Less than or equal to?

prev = acc;

prev = acc;

acc = (pop() <= acc);

acc = (pop() <= acc);

;<nowiki>op 0x27: ugt? (1 byte)</nowiki>

;<nowiki>op 0x27: ugt? (1 byte)</nowiki>

:Unsigned: Greater than?

:Unsigned: Greater than?

acc = (pop() > acc);

acc = (pop() > acc);

</source>

</source>

;<nowiki>op 0x29: uge? (1 byte)</nowiki>

;<nowiki>op 0x29: uge? (1 byte)</nowiki>

:Unsigned: Greather than or equal to?

:Unsigned: Greather than or equal to?

acc = (pop() >= acc);

acc = (pop() >= acc);

</source>

</source>

;<nowiki>op 0x2b: ult? (1 byte)</nowiki>

;<nowiki>op 0x2b: ult? (1 byte)</nowiki>

:Unsigned: Less than?

:Unsigned: Less than?

acc = (pop() < acc);

acc = (pop() < acc);

</source>

</source>

;<nowiki>op 0x2d: ule? (1 byte)</nowiki>

;<nowiki>op 0x2d: ule? (1 byte)</nowiki>

:Unsigned: Less than or equal to?

:Unsigned: Less than or equal to?

acc = (pop() >= acc);

acc = (pop() >= acc);

</source>

</source>

;<nowiki>op 0x2f: bt B relpos (2 bytes)</nowiki>

;<nowiki>op 0x2f: bt B relpos (2 bytes)</nowiki>

:Branch relative if true

:Branch relative if true

if (acc) pc += relpos;

if (acc) pc += relpos;

</source>

</source>

;<nowiki>op 0x31: bnt B relpos (2 bytes)</nowiki>

;<nowiki>op 0x31: bnt B relpos (2 bytes)</nowiki>

:Branch relative if not true

:Branch relative if not true

if (!acc) pc += relpos;

if (!acc) pc += relpos;

</source>

</source>

;<nowiki>op 0x33: jmp B relpos (2 bytes)</nowiki>

;<nowiki>op 0x33: jmp B relpos (2 bytes)</nowiki>

:Jump

:Jump

pc += relpos;

pc += relpos;

</source>

</source>

;<nowiki>op 0x35: ldi B data (2 bytes)</nowiki>

;<nowiki>op 0x35: ldi B data (2 bytes)</nowiki>

:Load data immediate

:Load data immediate

acc = data;

acc = data;

</source>

</source>

;<nowiki>op 0x37: push (1 byte)</nowiki>

;<nowiki>op 0x37: push (1 byte)</nowiki>

:Push to stack

:Push to stack

push(acc)

push(acc)

</source>

</source>

;<nowiki>op 0x39: pushi B data (2 bytes)</nowiki>

;<nowiki>op 0x39: pushi B data (2 bytes)</nowiki>

:Push immediate

:Push immediate

push(data)

push(data)

</source>

</source>

;<nowiki>op 0x3b: toss (1 byte)</nowiki>

;<nowiki>op 0x3b: toss (1 byte)</nowiki>

:TOS subtract

:TOS subtract

pop();

pop();

</source>

</source>

;<nowiki>op 0x3d: dup (1 byte)</nowiki>

;<nowiki>op 0x3d: dup (1 byte)</nowiki>

:Duplicate TOS element

:Duplicate TOS element

push(*TOS);

push(*TOS);

</source>

</source>

;<nowiki>op 0x3e: link W size (3 bytes)</nowiki>

;<nowiki>op 0x3e: link W size (3 bytes)</nowiki>

;<nowiki>op 0x3f: link B size (2 bytes)</nowiki>

;<nowiki>op 0x3f: link B size (2 bytes)</nowiki>

sp += (size * 2);

sp += (size * 2);

</source>

</source>

:Call inside script.

:Call inside script.

:(See description below)

:(See description below)

sp -= (framesize + 2 + &rest_modifier);

sp -= (framesize + 2 + &rest_modifier);

&rest_modifier = 0;

&rest_modifier = 0;

;<nowiki>op 0x43: callk B kfunct, B kparams (3 bytes)</nowiki>

;<nowiki>op 0x43: callk B kfunct, B kparams (3 bytes)</nowiki>

:Call kernel function (see the [[SCI/Specifications/SCI virtual machine/Kernel functions|Kernel functions]] section)

:Call kernel function (see the [[SCI/Specifications/SCI virtual machine/Kernel functions|Kernel functions]] section)

sp -= (kparams + 2 + &rest_modifier);

sp -= (kparams + 2 + &rest_modifier);

&rest_modifier = 0;

&rest_modifier = 0;

:Call base script

:Call base script

:(See description below)

:(See description below)

sp -= (framesize + 2 + &rest_modifier);

sp -= (framesize + 2 + &rest_modifier);

&rest_modifier = 0;

&rest_modifier = 0;

:Call external script

:Call external script

:(See description below)

:(See description below)

sp -= (framesize + 2 + &rest_modifier);

sp -= (framesize + 2 + &rest_modifier);

&rest_modifier = 0;

&rest_modifier = 0;

:Send looks up the supplied selector(s) in the object pointed to by the accumulator. If the selector is a variable selector, it is read (to the accumulator) if it was sent for with zero parameters. If a parameter was supplied, this selector is set to that parameter. Method selectors are called with the specified parameters.

:Send looks up the supplied selector(s) in the object pointed to by the accumulator. If the selector is a variable selector, it is read (to the accumulator) if it was sent for with zero parameters. If a parameter was supplied, this selector is set to that parameter. Method selectors are called with the specified parameters.

:The selector(s) and parameters are retreived from the stack frame. Send first looks up the selector ID at the bottom of the frame, then retreives the number of parameters, and, eventually, the parameters themselves. This algorithm is iterated until all of the stack frame has been "used up". Example:

:The selector(s) and parameters are retreived from the stack frame. Send first looks up the selector ID at the bottom of the frame, then retreives the number of parameters, and, eventually, the parameters themselves. This algorithm is iterated until all of the stack frame has been "used up". Example:

; This is an example for usage of the SCI send operation

; This is an example for usage of the SCI send operation

   pushi x      ; push the selector ID of x

   pushi x      ; push the selector ID of x

::set if the accumulator is to be used as additional index  

::set if the accumulator is to be used as additional index  

:::Because it is so hard to explain, I have made a transcription of it here:

:::Because it is so hard to explain, I have made a transcription of it here:

short *vars[4];

short *vars[4];

;<nowiki>op 0x5d: selfID (1 bytes)</nowiki>

;<nowiki>op 0x5d: selfID (1 bytes)</nowiki>

:Get 'self' identity: SCI uses heap pointers to identify objects, so this operation sets the accumulator to the address of the current object.

:Get 'self' identity: SCI uses heap pointers to identify objects, so this operation sets the accumulator to the address of the current object.

;<nowiki>op 0x61: pprev (1 bytes)</nowiki>

;<nowiki>op 0x61: pprev (1 bytes)</nowiki>

:Push prev: Pushes the value of the prev register, set by the last comparison bytecode (eq?, lt?, etc.), on the stack.

:Push prev: Pushes the value of the prev register, set by the last comparison bytecode (eq?, lt?, etc.), on the stack.

;<nowiki>op 0x73: lofsa B offset (2 bytes)</nowiki>

;<nowiki>op 0x73: lofsa B offset (2 bytes)</nowiki>

:Load Offset to Accumulator:

:Load Offset to Accumulator:

:Adds a value to the post-operation pc and stores the result in the accumulator.

:Adds a value to the post-operation pc and stores the result in the accumulator.

;<nowiki>op 0x75: lofss B offset (2 bytes)</nowiki>

;<nowiki>op 0x75: lofss B offset (2 bytes)</nowiki>

:Load Offset to Stack:

:Load Offset to Stack:

:Adds a value to the post-operation pc and pushes the result on the stack.

:Adds a value to the post-operation pc and pushes the result on the stack.

;<nowiki>op 0x77: push0 (1 bytes)</nowiki>

;<nowiki>op 0x77: push0 (1 bytes)</nowiki>

:Push 0:

:Push 0:

;<nowiki>op 0x79: push1 (1 bytes)</nowiki>

;<nowiki>op 0x79: push1 (1 bytes)</nowiki>

:Push 1:

:Push 1:

;<nowiki>op 0x7b: push2 (1 bytes)</nowiki>

;<nowiki>op 0x7b: push2 (1 bytes)</nowiki>

:Push 2:

:Push 2:

;<nowiki>op 0x7d: pushSelf (1 bytes)</nowiki>

;<nowiki>op 0x7d: pushSelf (1 bytes)</nowiki>

:Push self:

:Push self: