{File name LispStkScan.mc
Description:  DandeLion InterLisp Emulator StkScan
Author: Charnley
Last modified: Charnley             2-May-84 12:09:41
Created:  2-May-84 11:42:53
}


{- - - - - - - - - - - - - - - - - - - - - - - - - -
 57      STKSCAN     0        0                  \STKSCAN

	TOS is VAR.
	NO! -- If TOS is not litatom, punt.
	Returns 24 bit pointer to cell where VAR is bound.

	NO! -- Note: must check VAR=NIL, and return pointer to NIL's
	value cell. (Free variable lookup algorithm fails if
	given NIL, at least on Dorado.)

	If variable was bound on stack, the value returned will
	be a pointer into stack space.
	If variable is not bound, value will be pointer to top
	level value cell.

- - - - - - - - - - - - - - - - - - - - - - - - - -}

@STKSCAN:	opcode[57'b],
	{free var lookup on tos, which is an atom}
{	look up variable in current frame; fill in binding pointer
	(chaining not implemented)

This code assumes that NAMETABLE is contiguous in real memory {either it is on the stack, or within a code header which is non-page crossing}

on Entry:	c1
uTOS	restored to TOS if fault
uTOSH	restored to TOSH if fault
PV	current frame (point to PV region)
Q	{uChain}  (odd) stack pointer to variable to be looked up (Pv + ib + 1)
rhTT, TT	virtual address of name table (usually function header)
L3	caller's return link at[L3, 10, fvCaller] also used with fvfixup after fault

uses during subroutine:
rhRx, Rx	real address of name table
PV	frame extension pointers (point to PV region)(travel up alinks)
uPV	save local PV
TOS	used
uChain	TOSH{chain}
rhTOSH	nRhS {set once at odd time; must be left}{*} used with TOSH{chain}
uName	TOSH{name} _ [UvCL + T/2 {- UvCL.nlocals} + UvCL.fvaroffset]
ntSize, offset, L0, L1

on Return:	c1
	preserves S, PV, PC, L2, uTOS, uTOSH
	smashes TOS, TOSH {but preserved in uTOS, uTOSH}
rhTT, TT	virtual address of free value
@(chain)	filled in binding pointer
L1	binding type{fvStack, fvGlobal} Dispatch pending

on Fault:	TOS _ uTOS, TOSH _ uTOSH, PV _ uPV
}
{	INITIALIZE:
		uTOS  _  TOS
		uTOSH  _ TOSH
		TOSH  _  name {from TOS}
		uChain  _  0
		uPV  _  PV
		L3  _  L3.StkScan
	enter at newFrame:   c1

}

	uPV _ PV, L3 _ L3.StkScan,	c1;
	uTOSH _ TOSH,	c2;
	uTOS _ TOSH _ TOS,	c3;

	uChain _ 0,	c1;
	,	c2;
	CALL[newFrame],	c3;

	Q _ rhTT, CANCELBR[$, 0F],	c1, at[L3.StkScan, 10, fvCaller];
	TOSH _ Q,	c2;
	TOS _ TT, GOTO[evalEND],	c3;

	PV _ uPV, GOTO[NoFixes],	c3, at[L3.StkScan, 10, fvfixup];

	{ E N D }