File [Pixel]<IFS>Sources>IfsBcplTricks.asm!1


; IfsBcplTricks.asm
; Copyright Xerox Corporation 1979, 1980

; Last modified February 29, 1980  7:22 PM by Taft
; - use new XMLoad instruction, make it work on non-XM Altos
; Last modified by Butterfield, October 10, 1979  8:15 PM
; - FramesCaller, make it work for extended calls - 10/10
; - swat extended calls to FrameSize, ReturnTo, and GotoLabel - 10/10
; - RetryCall, make extended call retryable - 10/9/79

; Derived from BcplTricks.asm:
; Last modified July 13, 1979  10:23 PM by Taft

callersFrame = 0
savedPC = 1
temp = 2
extraArguments = 3
XARGS = -4
XJMP = -3
XPC = -2

.dusr XJMP0 = 64034
.dusr XMLoad = 63420	; AC0 ← (@AC1 in bank AC0)
.dusr XMStore = 63421	; (@AC1 in bank AC0) ← AC3
.dusr swat = 77400

getframe = 370
return = 366

.ent FrameSize, MyFrame
.ent CallersFrame, FramesCaller
.ent CallFrame, GotoFrame
.ent CoCall, CoReturn
.ent ReturnTo, ReturnFrom
.ent GotoLabel, RetryCall

	.srel

FrameSize:	.FrameSize
MyFrame:	.MyFrame
CallersFrame:	.CallersFrame
FramesCaller:	.FramesCaller
CallFrame:	.CallFrame
GotoFrame:	.GotoFrame
CoCall:		.CoCall
CoReturn:	.CoReturn
ReturnTo:	.ReturnTo
ReturnFrom:	.ReturnFrom
GotoLabel:	.GotoLabel
RetryCall:	.RetryCall

	.nrel

; FrameSize(proc) returns the frame size required by proc.

.FrameSize:
	sta 3 savedPC,2
	mov 0 3
	lda 0 0,3
	lda 1 cMinus4
	and 1 0
	lda 1 cXJMP0
	sne 0 1
	 swat
	lda 0 2,3
	jmp Done

cMinus4: -4
cXJMP0: XJMP0

; MyFrame() returns pointer to current frame.

.MyFrame:
	mov 2 0
	jmp 1,3

; CallersFrame([f]) returns pointer to frame that calls f.
; Default f=current frame

.CallersFrame:
	sta 3 savedPC,2
	lda 1 0,3		;get number of arguments
	snz 1 1
	 mov 2 0		;use present frame
	mov 0 3
	lda 0 callersFrame,3
	jmp Done

; FramesCaller(foo) returns the address to which the caller of
; the frame foo sent control, provided that he made the call
; with a jsris or jsrii, and that there has been no monkey-business
; with the frame subsequently.
; If the call was not made with a jsris or jsrii it returns 0.
; If foo is omitted it defaults to the caller's frame.

.FramesCaller:
	sta 3 savedPC,2
	lda 1 0,3
	snz 1 1			; default the argument?
	 mov 2 0
	mov 0 3			; 3 has frame in question
	lda 3 callersFrame,3	; get frame of caller
	sta 3 temp,2		; save the frame in temp in case jsris

; figure out whether normal or extended caller
	sub 0 0			; assume normal (bank 0)
	lda 1 cXARGS
	add 3 1
	lda 3 savedPC,3
	se 1 3
	 jmp FcGetCallInst
	lda 0 XJMP-XARGS,3	; extended caller, set 0 to XJMP & 3
	lda 1 c3
	and 1 0
	lda 3 XPC-XARGS,3	; set 3 to XPC - 1
	adc 1 1
	add 1 3

; compute the address of the jsrxx instruction using ac3 for the pc
FcGetCallInst:
	sta 0 extraArguments 2	; save bank number
	adc 1 1			; backup the pc
	add 3 1
	XMLoad			; get the call instruction

; find out what the opcode is
	lda 3 opJsris
	sub 3 0
	lda 3 cLmask
	and 0 3 szr
	 jmp NotJsris
; calling instruction was jsris
	sta 3 extraArguments 2	; jsris gets indirect word from bank zero
	lda 1 temp,2		; jsris uses stack pointer for base
	jmp FcFinishUp

NotJsris: lda 3 opJsriiMinusJsris
	sub 3 0
;	lda 3 cLMask		; opJsriiMinusJsris = cLMask
	and 0 3 szr
	 jmp NotJsrii
; calling instruction was jsrii, uses instruction address for base

FcFinishUp:
; ac0 now has just the address field -- the opcode is zero.
; the next three instructions extend the sign of the address field, now in 0
	lda 3 c200
	andzl 0 3
	sub 3 0
; now add in the base (PC or frame) specified by the opcode
	add 0 1			; address of indirect word
	lda 0 extraArguments 2	; bank number
	XMLoad			; get the indirect word
	mov 0 3			; ac0 now has address of static
	lda 0 0,3		; get contents of static
	jmp Done

NotJsrii: mkzero 0 0	; return zero if can't recognize opcode
	jmp Done

c3:		3
c200:		200
opJsriiMinusJsris:	; (jsrii .)-(jsris 0) -- assembler chokes on this
cLmask:		177400
cRmask:		377
opJsris:	jsris 0


; CallFrame(destframe[, arg 1[, arg 2]])
; Sends control to the specified frame and links it back to this one.

.CallFrame:
	sta 3 savedPC,2
	mov 0 3
	sta 2 callersFrame,3
Callf1:	mov 1 0
	lda 1 extraArguments,2
Callf2:	mov 3 2
Done:
	lda 3 savedPC,2
	jmp 1,3

; GotoFrame(destframe[, arg 1[, arg 2]])
; Just like CallFrame, but doesn't plant the return link.
; This is like Mesa's transfer.

.GotoFrame:
	sta 3 savedPC,2
	mov 0 3
	jmp Callf1


; CoCall(a, b) = CallFrame(MyFrame()>>F.callersFrame, a, b)

.CoCall:
	sta 3 savedPC,2
	lda 3 callersFrame,2
	sta 2 callersFrame,3
	jmp Callf2

; CoReturn(a, b)
; Just like CoCall, but doesn't plant the return link

.CoReturn:
	sta 3 savedPC,2
	lda 2 callersFrame,2
	jmp Done

; ReturnTo(label)
; Does a return to the specified label

.ReturnTo:
	lda 2 callersFrame,2
	mov 0 3
	jmp 0,3

; GotoLabel(frame, label, v)
; Sends control to the specified label in the specified frame,
; and passes v in AC0

.GotoLabel:
	mov 0 3
	lda 0 extraArguments,2
	mov 3 2
	mov 1 3
	jsr 0,3	;in case proc head, must find #args in @ac3
	 1

; RetryCall(p1, p2)
; Repeats the call which appears to have given control to the caller
; of RetryCall with p1 and p2 as the first two arguments, and the other
; arguments unchanged

.RetryCall:
	nop
	lda 2 callersFrame,2
	lda 3 savedPC,2
	sta 0 temp,2
	lda 0 cXARGS
	add 2 0
	sne 3 0
	 jmp RetryXCall
	lda 0 temp,2
	jmp -1,3

RetryXCall:
	dsz XPC,2
	dsz XPC,2
	lda 0 temp,2
	jmp XJMP,2

cXARGS:	XARGS

; ReturnFrom(fnOrFrame, v)
; Looks for a frame f which is either equal to fnOrFrame,
; or has FramesCaller(f) equal to fnOrFrame.  It then cuts back
; the stack to f and simulates a return from f with v as the value.
; If it runs into trouble it returns 0

; local variables for this routine
fnOrFrame = 4
v = 5
nextFrame = 6
count = 7

.ReturnFrom:
	sta 3 savedPC,2
	jsr @getframe
	 count+1
	 nop
	lda 0 cRmask
	sta 0 count,2
	mov 2 3

; the frame we just looked at is in 3
RfLoop:	lda 0 callersFrame,3

; if we've looked at too many frames, give up
	dsz count 2

; if the next frame is 0, give up
	snz 0 0
	 jmp RfFailed

; if the next frame is equal to the last one, give up
	sne 0 3
	 jmp RfFailed
	sta 0 nextFrame,2

; is the next frame equal to fnOrFrame?
	lda 1 fnOrFrame,2
	sne 0 1
	 jmp FoundFrame

; is its caller equal to fnOrFrame?
	jsr .FramesCaller
	 1
	lda 1 fnOrFrame,2
	sne 0 1
	 jmp FoundFrame

; it's not the one we want; charge on
	lda 3 nextFrame,2
	jmp RfLoop

FoundFrame: lda 0 v,2
	lda 2 nextFrame,2
	lda 2 callersFrame,2	;get his caller (return FROM him)
	jmp Done

RfFailed: mkzero 0 0
	jsr @return

	.end