GOOL Interpreter

In the Crash games, the GOOL Interpreter is responsible for interpreting an object's executable bytecode. This bytecode instructs the interpreter to perform a specific sequence of operations that can conditionally or unconditionally alter specific characteristics of the object (ex. appearance, location, status, etc.), and should ultimately render the object according to its changing characteristics. As a result, the player observes a lively, animated, and interactive enemy, box, collectible item, or whatever other kind of in-game object it may be.

Interpretation

A single interpretation of an object's bytecode consists of the following steps:

1. Fetch the instruction at the object's program counter location
   • Read the instruction at the object's program counter location
   • Point the object's program counter to the location of the following instruction
2. Perform the operation specified by the fetched instruction
3. Continue repeating steps 1 and 2 until a suspending instruction is fetched

(A suspending instruction is typically either a RET, which marks the end of a block, or ANIF/ANIS, which change the object's current frame of animation.)

A single call to the GOOL interpreter routine with some desired object as its first argument results in a single interpretation of that object's bytecode. The GOOL bytecode interpreter routine expects an object that provides the following information:

• The location in its bytecode at which the interpreter shall begin its interpretation = object's program counter
• The location in its memory of a stack frame created for the interpretation = object's frame pointer
• The location in its memory at which the interpreter shall begin pushing the results of/popping the operands for interpreted instructions = object's stack pointer

Prior to an interpretation, each of these fields (program counter, frame pointer, stack pointer) is modified according to the object's current state [descriptor] and the type of interpretation.

Types of interpretation

Many separate interpretations of an object's bytecode can occur within a single frame. The GOOL interpreter routine can be called with the same object from up to 7 distinct locations in a single iteration of the game loop. Each of the 7 calls to the interpreter routine with that object, and thus the ensuing interpretations of its bytecode, occurs under a separate condition. The 7 interpretations are identified based on the conditions under which they occur, and are as follows:

• One that occurs at a specified rate, i.e. after a specific amount of time has elapsed since its previous occurrence. (Code Block interpretation)
• One that [always] occurs [for each frame]. (Trans Block interpretation)
• One that occurs whenever the object is sent an event and its current state specifies the location of an event service routine. (Event Block interpretation)
• One that occurs whenever the object is sent an event and: its current state does not specify an event service routine or its event service routine failed to return an event, and the event sent maps to an event handler. (Handles Block interpretation)
• One that occurs whenever the object changes state. (Head Block interpretation)
• One that occurs whenever the object changes state and its recent Trans Block interpretation was unsuccessful (*Trans Block interpretation)
• One that occurs when the object minimizes the distance during another object's query to 'find the nearest object', and the event sent for asynchronous handling (from the querying object) maps to an event handler. (*Handles Block interpretation)

Ignoring the details for now, the latter 2 types are just a Trans Block and Handles Block interpretation, respectively, although their calls cross-reference the interpreter routine from different locations. Thus, there are a total of 5 types. These 5 types are more simply viewed as 5 separate threads of execution of the object's bytecode. To demonstrate, here is the expanded game loop routine with only the calls to routines that have a descendant call to the interpreter routine:

 sub_80011FC4(levelid)
 { 
   ...	  
   C) sub_80011DD0 - Load entries and/or create universal game objects 
                     (HUD/display, Crash, Aku Aku, Shadows, Boxes, Fruit)
     1) sub_8001C6C8 - CreateObject() [called once for each object created]
     ...
   GAME LOOP:
   {
     1) Code for handling game pause/start button press
       A) If start pressed...
          i) If pause menu object does not exist....
             1) sub_8001C6C8 - CreateObject() [create pause menu object]
             ...
             else
             1) sub_80024040 - SendEvent() [destroy pause menu object]
             ...
     2) If Crash object does not exist: 
       A) sub_8002E98C - Create HUD and initialize level
          i) sub_8001C6C8 - CreateObject() [create HUD object]
          ii)sub_80026650 - Reinitialize Level
             1) sub_8001C6C8 - CreateObject() [create Crash object]
             ...
     3) Code for loading a new level if necessary
       A) If new level to load
          ...
          ii)sub_80011DD0 - Load entries and/or create universal game objects 
             1) sub_8001C6C8 - CreateObject() [called once for each object created]
             ...
     ...
     5) Spawn all objects in current zone [for those that have their respawn bit set]
       A) sub_80025928 - Spawn objects
          1) sub_8001BCC8 - SpawnObject() [called for each object spawned]
          ...
     ...
     9) Update all objects and create transformed primitives for them
       A) sub_8001D5EC - UpdateObjects()
          1) sub_8001DA0C - UpdateObject() [called for each existing object]
     ...
   } 
 }

Based on the above, consider an arbitrary frame of execution in terms of a single object. CreateObject() or SpawnObject() will not be called more than once [to create that object] in that frame; that is-the object is not created or spawned more than once, or even spawned after it is created and vice-versa. The object may not even be created/spawned in that frame because it either already exists or does not exist since the game has not requested it be created/spawned. If it is an existing object, it will also be updated only once in that frame. For a single object, the above can be reduced the following series of potential calls:

 sub_80011FC4(levelid)
 { 
   ...	  
   GAME LOOP:
   {
     ...
     CreateObject(obj,...) or SpawnObject(obj,...)
     ...
     SendEvent(src,obj,...)
     ...
     UpdateObject(obj)
   } 
 }

What the above leaves out, however, are the number of other locations at which a call to the SendEvent() routine reside. In fact, there is nothing preventing the object from being the recipient of more than one event sent (from potentially multiple sources) in a single frame. There may be an interpretation for each event sent to the object during that frame, and there is no limit on the number of events that can be sent. Thus, there may be many calls to SendEvent() [with the object as the recipient] in a single frame, but still only at most one call to CreateObject/SpawnObject() and UpdateObject(). Without getting too far off track, it is simply necessary to understand that each of these routines contains (or calls a routine that calls a routine that contains) a call to the interpreter routine:

 sub_80011FC4(levelid)
 { 
   ...	  
   GAME LOOP:
   {
     ...
     CreateObject(obj,...) or SpawnObject(obj,...)
       InitObject(obj, ...)
         ChangeObjectState(obj, ...)
           CreateObjectStackFrame(obj);
           obj->pc = obj->pchead;
           InterpretObject(obj, 3, &stateref); // # 1
         
     SendEvent(src,obj,...)
        -if there is an event service routine for the object (in its current state)
           CreateObjectStackFrame(obj);
           obj->pc = obj->pcevent;
           InterpretObject(obj, 8, &stateref); // # 2
        -if there is not an event service routine for the object (in its current state)
         or the event service routine failed to return an event
          -if the event maps to an event handler in the event->state/handler map
           CreateObjectStackFrame(obj);
           obj->pc = handlerlocation;
           InterpretObject(obj, 3, &stateref); // # 3
          -else
           ChangeObjectState(obj,state,...); *

     UpdateObject(obj)
      -if the object is able to animate
        -if there is a trans block to interpret for the object (in its current state)
           CreateObjectStackFrame(obj);
           obj->pc = obj->pctrans;
           InterpretObject(obj, 3, &stateref); // # 4
        -if at least n ticks have elapsed, where n is given by the 'wait' operand of the 
         most recently suspending animation type instruction of the object's code block 
           InterpretObject(obj, 4, &stateref); // # 5

   } 
 }

UNFINISHED Thus, a potential sequence of instruction reads as a result of multiple calls to the interpret 

routine for the same object in one iteration of the main game loop could be: 

Offset/address | Instruction

---------------|-------------

headBlock: 0x0 |      N

           0x4 |      N

           0x8 |      N

           0xC |      S

.....          |     

eventBlock:0x34|      N

           0x38|      N

           0x3C|      S

.....          |

transBlock:0x50|      N

           0x54|      N

           0x58|      N

           0x5C|      N

           0x60|      N

           0x64|      N

           0x68|      S

.....          |

codeBlock: 0x70|      N

           0x74|      N

           0x78|      N

           0x7C|      N

           0x80|      S

Where the offsets/addresses of the interpreted instructions from the object's instantiating 

executable entries' bytecode item are indicated in the left column along with labels at the offsets 

that are pointed to in their respective object fields of the same name, and whether the instructions 

either did not suspend execution-causing the next instruction in sequence to be read/interpreted 

(indicated by an N)-or did suspend execution-causing the interpreter routine to return to the callee 

(indicated by an S). 

These object fields/pointers (headBlock, eventBlock, transBlock, codeBlock) define, for some object, 

the absolute locations of 'blocks' in the object's code that the object's program counter will be 

changed to point at, prior to each respective type of interpretation [during the iteration of the 

game loop in which the object is created]. Equivalently, they define the respective entry points for 

4 separate -threads- of execution for an object-a head thread, an event thread, a trans thread, and 

a code thread. 3 of these object fields/pointers change whenever the object 'changes state', which 

is accomplished with the 'changeState()' routine. 

Opcode	Name	Encoding/Format	Explicit GOOL ops in	Explicit IMM. ops in	Implicit STACK ops in	Operation	Implicit STACK out	Explicit GOOL ops out	Description
0/0x00	ADD	00000000RRRRRRRRRRRRLLLLLLLLLLLL	L,R			O = L + R	O		add
1/0x01	SUB	00000001RRRRRRRRRRRRLLLLLLLLLLLL	L,R			O = L - R	O		subtract
2/0x02	MUL	00000010RRRRRRRRRRRRLLLLLLLLLLLL	L,R			O = L * R	O		multiply
3/0x03	DIV	00000011RRRRRRRRRRRRLLLLLLLLLLLL	L,R			O = L / R	O		divide
4/0X04	CEQ	00000100RRRRRRRRRRRRLLLLLLLLLLLL	L,R			O = (L == R), O = ((L ^ R) == 0)	O		check if equal
5/0x05	ANDL	00000101RRRRRRRRRRRRLLLLLLLLLLLL	L,R			O = (L && R), O = (L ? (R > 0) : 0)	O		logical and
6/0x06	ORL	00000110RRRRRRRRRRRRLLLLLLLLLLLL	L,R			O = (L || R)	O		logical or
7/0x07	ANDB	00000111RRRRRRRRRRRRLLLLLLLLLLLL	L,R			O = L & R	O		bitwise and
8/0x08	ORB	00001000RRRRRRRRRRRRLLLLLLLLLLLL	L,R			O = L | R	O		bitwise or
9/0x09	SLT	00001001RRRRRRRRRRRRLLLLLLLLLLLL	L,R			O = L < R	O		set less than
10/0x0A	SLE	00001010RRRRRRRRRRRRLLLLLLLLLLLL	L,R			O = (L <= R)	O		set less than or equal
11/0x0B	SGT	00001011RRRRRRRRRRRRLLLLLLLLLLLL	L,R			O = L > R	O		set greater than
12/0x0C	SGE	00001100RRRRRRRRRRRRLLLLLLLLLLLL	L,R			O = (L >= R)	O		set greater than or equal
13/0x0D	MOD	00001101RRRRRRRRRRRRLLLLLLLLLLLL	L,R			O = L % R	O		modulo
14/0x0E	XOR	00001110RRRRRRRRRRRRLLLLLLLLLLLL	L,R			O = L ^ R	O		exclusive or
15/0x0F	TST	00001111RRRRRRRRRRRRLLLLLLLLLLLL	L,R			O = (((L & R) ^ R) == 0)	O		test bit
16/0x10	RND	00010000AAAAAAAAAAAABBBBBBBBBBBB	A,B			O = B+(rand() % (A - B))	O		random
17/0x11	MOVE	00010001SSSSSSSSSSSSDDDDDDDDDDDD	S			D = S		[D]	move data
18/0x12	NOTL	00010010SSSSSSSSSSSSDDDDDDDDDDDD	S			D = (S == 0)		D	logical not
19/0x13	PATH	00010011AAAAAAAAAAAABBBBBBBBBBBB	(A),B	R = 0x100	[R,A]	varies	P	B	path progress
20/0x14	LEA	00010100SSSSSSSSSSSSDDDDDDDDDDDD	S			D = &S		D	load effective address
21/0x15	SHA	00010101RRRRRRRRRRRRLLLLLLLLLLLL	L,R			O = ((R < 0) ? (L >> -R) : (L << R))	O		arithmetic shift
22/0x16	PSHV	00010110AAAAAAAAAAAABBBBBBBBBBBB	[A,[B]]			[arg_buf = A] I = A; J = B;	[I,[J]]		push value to stack
23/0x17	NOTB	00010111SSSSSSSSSSSSDDDDDDDDDDDD				D = ~S		D	bitwise not
24/0x18	MOVC	000110000000RRRRRRIIIIIIIIIIIIII		R,C		see docs	O		move code pointer
25/0x19	ABS	00011001SSSSSSSSSSSSDDDDDDDDDDDD	S			D = (S < 0) ? -S: S		D	absolute value
26/0x1A	PAD	00011010000TDDDDSSPPBBBBBBBBBBBB		B,P,S,D,T		O = testctrls(instr,0)	O		test controller buttons
27/0x1B	SPD	00011011VVVVVVVVVVVVBBBBBBBBBBBB	V,B			S = B + ((V*gvel) >> 10)	S		calculate speed
28/0x1C	MSC	00011100PPPPSSSSSLLLXXXXXXXXXXXX	X	P,S,L		various; see docs	***	***	multi-purpose
29/0x1D	PRS	00011101PPPPPPPPPPPPDDDDDDDDDDDD	P,D			large calc; see docs	O		driven sine wave
30/0x1E	SSAW	00011110DDDDDDDDDDDDPPPPPPPPPPPP	M,P			O = (M + frameCount) % P	O		synchronized saw wave
31/0x1F	RGL	00011111000000000000IIIIIIIIIIII	I			O = globals[I >> 8]	O		read global variable
32/0x20	WGL	00100000SSSSSSSSSSSSIIIIIIIIIIII	I,S			globals[I << 8] = *S			write global variable
33/0x21	ANGD	00100001RRRRRRRRRRRRLLLLLLLLLLLL	L,R			O = angdist(L,R)			angle between
34/0x22	APCH	00100010RRRRRRRRRRRRLLLLLLLLLLLL	L,(R)	S = 0x100	[R,S]	O = approach(L,R,S)	O		approach a value
35/0x23	CVMR	00100011000IIIIIILLL000000000000		I,L		O = obj.link[L].colors[I]			color vector or matrix read
36/0x24	CVMW	00100011000IIIIIILLLCCCCCCCCCCCC	C	I,L		obj.link[L].colors[I] = C			color vector or matrix write
37/0x25	ROT	00100101RRRRRRRRRRRRLLLLLLLLLLLL	L,(R)		[R,S]	O = rotate(L,R,S,0)	O		approach an angle
38/0x26	PSHP	001001100AAAAAAAAAAABBBBBBBBBBBB	[A,[B]]			I = &A; J = &B;		[I,[J]]	push pointer to stack
39/0X27	ANID	00100111FFFFFFFFFFFFDDDDDDDDDDDD	F			D=&obj.global.anim[F>>5]		D	set animation
128/0x80	DBG	10000000RRRRRRRRRRRRLLLLLLLLLLLL	L,R						debug print ops (beta only)
129/0x81	NOP	10000001000000000000000000000000							no operation
130/0x82	CFL	10000010TTCCRRRRRRIIIIIIIIIIIIII		T,C,R,I					general control flow
	BRA	100000100000RRRRRRVVVVIIIIIIIIII		R,V,I					branch
	BNEZ	100000100001RRRRRRVVVVIIIIIIIIII		R,V,I					branch not equal zero
	BEQZ	100000100010RRRRRRVVVVIIIIIIIIII		R,V,I					branch equal zero
	CST	100000100100RRRRRRSSSSSSSSSSSSSS		R,S					change state
	CSNZ	100000100101RRRRRRSSSSSSSSSSSSSS		R,S					change state not zero
	CSEZ	100000100110RRRRRRSSSSSSSSSSSSSS		R,S					change state equal zero
	RET	100000101000RRRRRRIIIIIIIIIIIIII		R,I					return
131/0x83	ANIS	10000011HHTTTTTTSSSSSSSSSFFFFFFF		F,S,T,H			W		change animation sequence
132/0x84	ANIF	10000100HHTTTTTTFFFFFFFFFFFFFFFF	F	T,H			W		change animation frame
133/0x85	VECA	10000101CCCTTTBBBAAAVVVVVVVVVVVV	V	T,A,B,C			*	**	multi-purpose vector calcs
134/0x86	JAL	10000110VVVV000000IIIIIIIIIIIIII		I,V					jump and link
135/0x87	EVNT	10000111LLLAAARRRRRREEEEEEEEEEEE	E	L,A,R					send an event
136/0x88	RSTT	10001000TTCCRRRRRR**************		R,C,T,*	**				state return guard = true variant
137/0x89	RSTF	10001001TTCCRRRRRR**************		R,C,T,*	**				state return guard = false variant
138/0x8A	CHLD	10001010AAAATTTTTTTTSSSSSSCCCCCC		C,T,S,A	[C], arg[0 to A]				spawn children objects
139/0x8B	NTRY	10001011TTTTTTTTTTTTEEEEEEEEEEEE		T,E					multi-purpose page operation
140/0x8C	SNDA	10001100AAAAAAAAAAAABBBBBBBBBBBB	A,B						adjust audio levels
141/0x8D	SNDB	10001101VVVVRRRRRRSSSSSSSSSSSSS							play sound effect
142/0x8E	VECB	10001110CCCTTTBBBAAAVVVVVVVVVVVV	V	T,A,B,C					multi-purpose vector calcs
143/0x8F	EVNB	10001111LLLAAARRRRRREEEEEEEEEEEE	E	L,A,R					broadcast an event
144/0x90	EVNU	10010000LLLAAARRRRRREEEEEEEEEEEE	E	L,A,R					send event unknown variant
145/0x91	CHLF	10100000AAAATTTTTTTTSSSSSSCCCCCC		C,T,S,A	[C], arg[0 to A]				spawn children objects; no replacement if obj pool full

Specification Format	A	AAAAAAAAAAAA	AAAA	AAA (EVNT/EVNU/EVNB)	AAA (VECA/VECB)
Name		Value A	Argument Count	Argument Count	Vector A Index
Specification Format	B	BBBBBBBBBBBB	BBBBBBBBBBBB (PAD)	BBBBBBBBBBBB (SPD)	BBB
Name		Value B	Controller Buttons	Base Speed	Vector B Index
Specification Format	C	CCCCCCCCCCCC	CCCCCC	CCC	CC
Name		Color Value	Spawn Count	Vector C Index	Conditional Check Type
Specification Format	D	DDDDDDDDDDDD	DDDDDDDDDDDD (PRS)	DDDD
Name		Destination	Wave Phase	Directional Buttons
Specification Format	E	EEEEEEEEEEEE (NTRY)	EEEEEEEEEEEE (EVNT/EVNU/EVNB)
Name		Entry	Event
Specification Format	F	FFFFFFFFFFFFFFFF	FFFFFFFFFFFF	FFFFFFF
Name		Animation Frame	Animation Descriptor Offset	Animation Frame
Specification Format	H	HH
Name		Horizontal Flip
Specification Format	I	IIIIIIIIIIIIII	IIIIIIIIIIII	IIIIIIIIII	IIIIII
Name		Immediate Code Location	Global Variable Index	Immediate Branch Offset	Color Index
Specification Format	L	LLLLLLLLLLLL	LLL
Name		Left Operand	Object Link Index
Specification Format	P	PPPPPPPPPPPP	PPPP	PP
Name		Wave Period	Primary Operation Subtype	Primary Check Type
Specification Format	R	RRRRRRRRRRRR	RRRRRR
Name		Right Operand	Object Register Index
Specification Format	S	SSSSSSSSSSSSSS	SSSSSSSSSSSS	SSSSSSSSS	SSSSSS
Name		State	Source	Animation Sequence Index	Subtype
Specification Format		SSSSS	SS
Name		Secondary Operation Subtype	Secondary Check Type
Specification Format	T	TTTTTTTTTTTT	TTTTTTTT	TTTTTT	TTT
Name		Operation Subtype	(Object) Type	Time	Operation Subtype
Specification Format		TT	T
Name		Operation Subtype	Truth Invert Toggle
Specification Format	V	VVVVVVVVVVVV	VVVV	VVVV (SNDB)
Name		Velocity	Variable Count	Volume

State Return Instruction Table

Opcode	Name	Encoding/Format	Explicit IMM. ops in	Description
136/0x88	RSTT	10001000TTCCRRRRRR**************	R,C,T,*	state return guard = true variant
	RST	100010000100RRRRRRSSSSSSSSSSSSSS	R,S	state return guard = true
	RSNT	100010000101RRRRRRSSSSSSSSSSSSSS	R,S	state return if nonzero guard = true
	RSZT	100010000110RRRRRRSSSSSSSSSSSSSS	R,S	state return if equal zero guard = true
	RSCT	100010000111RRRRRRSSSSSSSSSSSSSS	R,S	state return eval prev cond guard = true
	RNT	100010001000RRRRRRxxxxxxxxxxxxxx	R	null return guard = true
	RNNT	100010001001RRRRRRxxxxxxxxxxxxxx	R	null return if nonzero guard = true
	RNZT	100010001010RRRRRRxxxxxxxxxxxxxx	R	null return if equal zero guard = true
	RNCT	100010001011RRRRRRxxxxxxxxxxxxxx	R	null return eval prev cond guard = true
	GDT	100010001100RRRRRRxxxxxxxxxxxxxx	R	guard = true
	GNT	100010001101RRRRRRxxxxxxxxxxxxxx	R	if nonzero guard = true
	GZT	100010001110RRRRRRxxxxxxxxxxxxxx	R	if equal zero guard = true
	GCT	100010001111RRRRRRxxxxxxxxxxxxxx	R	eval prev cond guard = true
	GBNT	100010000001RRRRRRVVVVIIIIIIIIII	R,V,I	if nonzero guard = true else branch
	GBZT	100010000010RRRRRRVVVVIIIIIIIIII	R,V,I	if equal zero guard = true else branch
137/0x89	RSTF	10001001TTCCRRRRRR**************	R,C,T,*	state return guard = false variant
	RSF	100010000100RRRRRRSSSSSSSSSSSSSS	R,S	state return guard = false
	RSNF	100010000101RRRRRRSSSSSSSSSSSSSS	R,S	state return if nonzero guard = false
	RSZF	100010000110RRRRRRSSSSSSSSSSSSSS	R,S	state return if equal zero guard = false
	RSCF	100010000111RRRRRRSSSSSSSSSSSSSS	R,S	state return eval prev cond guard = false
	RNF	100010001000RRRRRRxxxxxxxxxxxxxx	R	null return guard = false
	RNNF	100010001001RRRRRRxxxxxxxxxxxxxx	R	null return if nonzero guard = false
	RNZF	100010001010RRRRRRxxxxxxxxxxxxxx	R	null return if equal zero guard = false
	RNCF	100010001011RRRRRRxxxxxxxxxxxxxx	R	null return eval prev cond guard = false
	GDF	100010001100RRRRRRxxxxxxxxxxxxxx	R	guard = false
	GNF	100010001101RRRRRRxxxxxxxxxxxxxx	R	if nonzero guard = false
	GZF	100010001110RRRRRRxxxxxxxxxxxxxx	R	if equal zero guard = false
	GCF	100010001111RRRRRRxxxxxxxxxxxxxx	R	eval prev cond guard = false
	GBNF	100010000001RRRRRRVVVVIIIIIIIIII	R,V,I	if nonzero guard = false else branch
	GBZF	100010000010RRRRRRVVVVIIIIIIIIII	R,V,I	if equal zero guard = false else branch