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ack/doc/em/em.i
ceriel 628b9699e8 adapted to new ip_spec.t
1988-03-15 13:17:42 +00:00

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{ This is an interpreter for EM. It serves as the official machine
definition. This interpreter must run on a machine which supports
arithmetic with words and memory offsets.
Certain aspects of the definition are over specified. In particular:
1. The representation of an address on the stack need not be the
numerical value of the memory location.
2. The state of the stack is not defined after a trap has aborted
an instruction in the middle. For example, it is officially un-
defined whether the second operand of an ADD instruction has
been popped or not if the first one is undefined ( -32768 or
unsigned 32768).
3. The memory layout is implementation dependent. Only the most
basic checks are performed whenever memory is accessed.
4. The representation of an integer or set on the stack is not fixed
in bit order.
5. The format and existence of the procedure descriptors depends on
the implementation.
6. The result of the compare operators CMI etc. are -1, 0 and 1
here, but other negative and positive values will do and they
need not be the same each time.
7. The shift count for SHL, SHR, ROL and ROR must be in the range 0
to object size in bits - 1. The effect of a count not in this
range is undefined.
}
.bp
{$i256} {$d+}
program em(tables,prog,input,output);
label 8888,9999;
const
t15 = 32768; { 2**15 }
t15m1 = 32767; { 2**15 -1 }
t16 = 65536; { 2**16 }
t16m1 = 65535; { 2**16 -1 }
t31m1 = 2147483647; { 2**31 -1 }
wsize = 2; { number of bytes in a word }
asize = 2; { number of bytes in an address }
fsize = 4; { number of bytes in a floating point number }
maxret =4; { number of words in the return value area }
signbit = t15; { the power of two indicating the sign bit }
negoff = t16; { the next power of two }
maxsint = t15m1; { the maximum signed integer }
maxuint = t16m1; { the maximum unsigned integer }
maxdbl = t31m1; { the maximum double signed integer }
maxadr = t16m1; { the maximum address }
maxoffs = t15m1; { the maximum offset from an address }
maxbitnr= 15; { the number of the highest bit }
lineadr = 0; { address of the line number }
fileadr = 4; { address of the file name }
maxcode = 8191; { highest byte in code address space }
maxdata = 8191; { highest byte in data address space }
{ format of status save area }
statd = 4; { how far is static link from lb }
dynd = 2; { how far is dynamic link from lb }
reta = 0; { how far is the return address from lb }
savsize = 4; { size of save area in bytes }
{ procedure descriptor format }
pdlocs = 0; { offset for size of local variables in bytes }
pdbase = asize; { offset for the procedure base }
pdsize = 4; { size of procedure descriptor in bytes = 2*asize }
{ header words }
NTEXT = 1;
NDATA = 2;
NPROC = 3;
ENTRY = 4;
NLINE = 5;
SZDATA = 6;
escape1 = 254; { escape to secondary opcodes }
escape2 = 255; { escape to tertiary opcodes }
undef = signbit; { the range of integers is -32767 to +32767 }
{ error codes }
EARRAY = 0; ERANGE = 1; ESET = 2; EIOVFL = 3; EFOVFL = 4;
EFUNFL = 5; EIDIVZ = 6; EFDIVZ = 7; EIUND = 8; EFUND = 9;
ECONV = 10; ESTACK = 16; EHEAP = 17; EILLINS = 18; EODDZ = 19;
ECASE = 20; EMEMFLT = 21; EBADPTR = 22; EBADPC = 23; EBADLAE = 24;
EBADMON = 25; EBADLIN = 26; EBADGTO = 27;
.ne 20
.bp
{---------------------------------------------------------------------------}
{ Declarations }
{---------------------------------------------------------------------------}
type
bitval= 0..1; { one bit }
bitnr= 0..maxbitnr; { bits in machine words are numbered 0 to 15 }
byte= 0..255; { memory is an array of bytes }
adr= {0..maxadr} long; { the range of addresses }
word= {0..maxuint} long;{ the range of unsigned integers }
offs= -maxoffs..maxoffs; { the range of signed offsets from addresses }
size= 0..maxoffs; { the range of sizes is the positive offsets }
sword= {-signbit..maxsint} long; { the range of signed integers }
full= {-maxuint..maxuint} long; { intermediate results need this range }
double={-maxdbl..maxdbl} long; { double precision range }
bftype= (andf,iorf,xorf); { tells which boolean operator needed }
insclass=(prim,second,tert); { tells which opcode table is in use }
instype=(implic,explic); { does opcode have implicit or explicit operand }
iflags= (mini,short,sbit,wbit,zbit,ibit);
ifset= set of iflags;
mnem = ( NON,
AAR, ADF, ADI, ADP, ADS, ADU,XAND, ASP, ASS, BEQ,
BGE, BGT, BLE, BLM, BLS, BLT, BNE, BRA, CAI, CAL,
CFF, CFI, CFU, CIF, CII, CIU, CMF, CMI, CMP, CMS,
CMU, COM, CSA, CSB, CUF, CUI, CUU, DCH, DEC, DEE,
DEL, DUP, DUS, DVF, DVI, DVU, EXG, FEF, FIF, FIL,
GTO, INC, INE, INL, INN, IOR, LAE, LAL, LAR, LDC,
LDE, LDF, LDL, LFR, LIL, LIM, LIN, LNI, LOC, LOE,
LOF, LOI, LOL, LOR, LOS, LPB, LPI, LXA, LXL, MLF,
MLI, MLU, MON, NGF, NGI, NOP, RCK, RET, RMI, RMU,
ROL, ROR, RTT, SAR, SBF, SBI, SBS, SBU, SDE, SDF,
SDL,XSET, SIG, SIL, SIM, SLI, SLU, SRI, SRU, STE,
STF, STI, STL, STR, STS, TEQ, TGE, TGT, TLE, TLT,
TNE, TRP, XOR, ZEQ, ZER, ZGE, ZGT, ZLE, ZLT, ZNE,
ZRE, ZRF, ZRL);
dispatch = record
iflag: ifset;
instr: mnem;
case instype of
implic: (implicit:sword);
explic: (ilength:byte);
end;
var
code: packed array[0..maxcode] of byte; { code space }
data: packed array[0..maxdata] of byte; { data space }
retarea: array[1..maxret ] of word; { return area }
pc,lb,sp,hp,pd: adr; { internal machine registers }
i: integer; { integer scratch variable }
s,t :word; { scratch variables }
sz:size; { scratch variables }
ss,st: sword; { scratch variables }
k :double; { scratch variables }
j:size; { scratch variable used as index }
a,b:adr; { scratch variable used for addresses }
dt,ds:double; { scratch variables for double precision }
rt,rs,x,y:real; { scratch variables for real }
found:boolean; { scratch }
opcode: byte; { holds the opcode during execution }
iclass: insclass; { true for escaped opcodes }
dispat: array[insclass,byte] of dispatch;
retsize:size; { holds size of last LFR }
insr: mnem; { holds the instructionnumber }
halted: boolean; { normally false }
exitstatus:word; { parameter of MON 1 }
ignmask:word; { ignore mask for traps }
uerrorproc:adr; { number of user defined error procedure }
intrap:boolean; { Set when executing trap(), to catch recursive calls}
trapval:byte; { Set to number of last trap }
header: array[1..8] of adr;
tables: text; { description of EM instructions }
prog: file of byte; { program and initialized data }
.ne 20
.sp 2
{---------------------------------------------------------------------------}
{ Various check routines }
{---------------------------------------------------------------------------}
{ Only the most basic checks are performed. These routines are inherently
implementation dependent. }
procedure trap(n:byte); forward;
procedure memadr(a:adr);
begin if (a>maxdata) or ((a<sp) and (a>=hp)) then trap(EMEMFLT) end;
procedure wordadr(a:adr);
begin memadr(a); if (a mod wsize<>0) then trap(EBADPTR) end;
procedure chkadr(a:adr; s:size);
begin memadr(a); memadr(a+s-1); { assumption: size is ok }
if s<wsize
then begin if a mod s<>0 then trap(EBADPTR) end
else if a mod wsize<>0 then trap(EBADPTR)
end;
procedure newpc(a:double);
begin if (a<0) or (a>maxcode) then trap(EBADPC); pc:=a end;
procedure newsp(a:adr);
begin if (a>lb) or (a<hp) or (a mod wsize<>0) then trap(ESTACK); sp:=a end;
procedure newlb(a:adr);
begin if (a<sp) or (a mod wsize<>0) then trap(ESTACK); lb:=a end;
procedure newhp(a:adr);
begin if (a>sp) or (a>maxdata+1) or (a mod wsize<>0)
then trap(EHEAP); hp:=a
end;
function argc(a:double):sword;
begin if (a<-signbit) or (a>maxsint) then trap(EILLINS); argc:=a end;
function argd(a:double):double;
begin if (a<-maxdbl) or (a>maxdbl) then trap(EILLINS); argd:=a end;
function argl(a:double):offs;
begin if (a<-maxoffs) or (a>maxoffs) then trap(EILLINS); argl:=a end;
function argg(k:double):adr;
begin if (k<0) or (k>maxadr) then trap(EILLINS); argg:=k end;
function argf(a:double):offs;
begin if (a<-maxoffs) or (a>maxoffs) then trap(EILLINS); argf:=a end;
function argn(a:double):word;
begin if (a<0) or (a>maxuint) then trap(EILLINS); argn:=a end;
function args(a:double):size;
begin if (a<=0) or (a>maxoffs)
then trap(EODDZ)
else if (a mod wsize)<>0 then trap(EODDZ);
args:=a ;
end;
function argz(a:double):size;
begin if (a<0) or (a>maxoffs)
then trap(EODDZ)
else if (a mod wsize)<>0 then trap(EODDZ);
argz:=a ;
end;
function argo(a:double):size;
begin if (a<=0) or (a>maxoffs)
then trap(EODDZ)
else if (a mod wsize<>0) and (wsize mod a<>0) then trap(EODDZ);
argo:=a ;
end;
function argw(a:double):size;
begin if (a<=0) or (a>maxoffs) or (a>maxuint)
then trap(EODDZ)
else if (a mod wsize)<>0 then trap(EODDZ);
argw:=a ;
end;
function argp(a:double):size;
begin if (a<0) or (a>=header[NPROC]) then trap(EILLINS); argp:=a end;
function argr(a:double):word;
begin if (a<0) or (a>2) then trap(EILLINS); argr:=a end;
procedure argwf(s:double);
begin if argw(s)<>fsize then trap(EILLINS) end;
function szindex(s:double):integer;
begin s:=argw(s); if (s mod wsize <> 0) or (s>2*wsize) then trap(EILLINS);
szindex:=s div wsize
end;
function locadr(l:double):adr;
begin l:=argl(l); if l<0 then locadr:=lb+l else locadr:=lb+l+savsize end;
function signwd(w:word):sword;
begin if w = undef then trap(EIUND);
if w >= signbit then signwd:=w-negoff else signwd:=w
end;
function dosign(w:word):sword;
begin if w >= signbit then dosign:=w-negoff else dosign:=w end;
function unsign(w:sword):word;
begin if w<0 then unsign:=w+negoff else unsign:=w end;
function chopw(dw:double):word;
begin chopw:=dw mod negoff end;
function fitsw(w:full;trapno:byte):word;
{ checks whether value fits in signed word, returns unsigned representation}
begin
if (w>maxsint) or (w<-signbit) then
begin trap(trapno);
if w<0 then fitsw:=negoff- (-w)mod negoff
else fitsw:=w mod negoff;
end
else fitsw:=unsign(w)
end;
function fitd(w:full):double;
begin
if abs(w) > maxdbl then trap(ECONV);
fitd:=w
end;
.ne 20
.sp 2
{---------------------------------------------------------------------------}
{ Memory access routines }
{---------------------------------------------------------------------------}
{ memw returns a machine word as an unsigned integer
memb returns a single byte as a positive integer: 0 <= memb <= 255
mems(a,s) fetches an object smaller than a word and returns a word
store(a,v) stores the word v at machine address a
storea(a,v) stores the address v at machine address a
storeb(a,b) stores the byte b at machine address a
stores(a,s,v) stores the s least significant bytes of a word at address a
memi returns an offset from the instruction space
Note that the procedure descriptors are part of instruction space.
nextpc returns the next byte addressed by pc, incrementing pc
lino changes the line number word.
filna changes the pointer to the file name.
All routines check to make sure the address is within range and valid for
the size of the object. If an addressing error is found, a trap occurs.
}
function memw(a:adr):word;
var b:word; i:integer;
begin wordadr(a); b:=0;
for i:=wsize-1 downto 0 do b:=256*b + data[a+i] ;
memw:=b
end;
function memd(a:adr):double; { Always signed }
var b:double; i:integer;
begin wordadr(a); b:=data[a+2*wsize-1];
if b>=128 then b:=b-256;
for i:=2*wsize-2 downto 0 do b:=256*b + data[a+i] ;
memd:=b
end;
function mema(a:adr):adr;
var b:adr; i:integer;
begin wordadr(a); b:=0;
for i:=asize-1 downto 0 do b:=256*b + data[a+i] ;
mema:=b
end;
function mems(a:adr;s:size):word;
var i:integer; b:word;
begin chkadr(a,s); b:=0; for i:=1 to s do b:=b*256+data[a+s-i]; mems:=b end;
function memb(a:adr):byte;
begin memadr(a); memb:=data[a] end;
procedure store(a:adr; x:word);
var i:integer;
begin wordadr(a);
for i:=0 to wsize-1 do
begin data[a+i]:=x mod 256; x:=x div 256 end
end;
procedure storea(a:adr; x:adr);
var i:integer;
begin wordadr(a);
for i:=0 to asize-1 do
begin data[a+i]:=x mod 256; x:=x div 256 end
end;
procedure stores(a:adr;s:size;v:word);
var i:integer;
begin chkadr(a,s);
for i:=0 to s-1 do begin data[a+i]:=v mod 256; v:=v div 256 end;
end;
procedure storeb(a:adr; b:byte);
begin memadr(a); data[a]:=b end;
function memi(a:adr):adr;
var b:adr; i:integer;
begin if (a mod wsize<>0) or (a+asize-1>maxcode) then trap(EBADPTR); b:=0;
for i:=asize-1 downto 0 do b:=256*b + code[a+i] ;
memi:=b
end;
function nextpc:byte;
begin if pc>=pd then trap(EBADPC); nextpc:=code[pc]; newpc(pc+1) end;
procedure lino(w:word);
begin store(lineadr,w) end;
procedure filna(a:adr);
begin storea(fileadr,a) end;
.ne 20
.sp 2
{---------------------------------------------------------------------------}
{ Stack Manipulation Routines }
{---------------------------------------------------------------------------}
{ push puts a word on the stack
pushsw takes a signed one word integer and pushes it on the stack
pop removes a machine word from the stack and delivers it as a word
popsw removes a machine word from the stack and delivers a signed integer
pusha pushes an address on the stack
popa removes a machine word from the stack and delivers it as an address
pushd pushes a double precision number on the stack
popd removes two machine words and returns a double precision integer
pushr pushes a float (floating point) number on the stack
popr removes several machine words and returns a float number
pushx puts an object of arbitrary size on the stack
popx removes an object of arbitrary size
}
procedure push(x:word);
begin newsp(sp-wsize); store(sp,x) end;
procedure pushsw(x:sword);
begin newsp(sp-wsize); store(sp,unsign(x)) end;
function pop:word;
begin pop:=memw(sp); newsp(sp+wsize) end;
function popsw:sword;
begin popsw:=signwd(pop) end;
procedure pusha(x:adr);
begin newsp(sp-asize); storea(sp,x) end;
function popa:adr;
begin popa:=mema(sp); newsp(sp+asize) end;
procedure pushd(y:double);
begin { push double integer onto the stack } newsp(sp-2*wsize) end;
function popd:double;
begin { pop double integer from the stack } newsp(sp+2*wsize); popd:=0 end;
procedure pushr(z:real);
begin { Push a float onto the stack } newsp(sp-fsize) end;
function popr:real;
begin { pop float from the stack } newsp(sp+fsize); popr:=0.0 end;
procedure pushx(objsize:size; a:adr);
var i:integer;
begin
if objsize<wsize
then push(mems(a,objsize))
else for i:=1 to objsize div wsize do push(memw(a+objsize-wsize*i))
end;
procedure popx(objsize:size; a:adr);
var i:integer;
begin
if objsize<wsize
then stores(a,objsize,pop)
else for i:=1 to objsize div wsize do store(a-wsize+wsize*i,pop)
end;
.ne 20
.sp 2
{---------------------------------------------------------------------------}
{ Bit manipulation routines (extract, shift, rotate) }
{---------------------------------------------------------------------------}
procedure sleft(var w:sword); { 1 bit left shift }
begin w:= dosign(fitsw(2*w,EIOVFL)) end;
procedure suleft(var w:word); { 1 bit left shift }
begin w := chopw(2*w) end;
procedure sdleft(var d:double); { 1 bit left shift }
begin { shift two word signed integer } end;
procedure sright(var w:sword); { 1 bit right shift with sign extension }
begin if w >= 0 then w := w div 2 else w := (w-1) div 2 end;
procedure suright(var w:word); { 1 bit right shift without sign extension }
begin w := w div 2 end;
procedure sdright(var d:double); { 1 bit right shift }
begin { shift two word signed integer } end;
procedure rleft(var w:word); { 1 bit left rotate }
begin if w >= t15
then w:=(w-t15)*2 + 1
else w:=w*2
end;
procedure rright(var w:word); { 1 bit right rotate }
begin if w mod 2 = 1
then w:=w div 2 + t15
else w:=w div 2
end;
function sextend(w:word;s:size):word;
var i:size;
begin
for i:=1 to (wsize-s)*8 do rleft(w);
for i:=1 to (wsize-s)*8 do sright(w);
sextend:=w;
end;
function bit(b:bitnr; w:word):bitval; { return bit b of the word w }
var i:bitnr;
begin for i:= 1 to b do rright(w); bit:= w mod 2 end;
function bf(ty:bftype; w1,w2:word):word; { return boolean fcn of 2 words }
var i:bitnr; j:word;
begin j:=0;
for i:= maxbitnr downto 0 do
begin j := 2*j;
case ty of
andf: if bit(i,w1)+bit(i,w2) = 2 then j:=j+1;
iorf: if bit(i,w1)+bit(i,w2) > 0 then j:=j+1;
xorf: if bit(i,w1)+bit(i,w2) = 1 then j:=j+1
end
end;
bf:=j
end;
{---------------------------------------------------------------------------}
{ Array indexing
{---------------------------------------------------------------------------}
function arraycalc(c:adr):adr; { subscript calculation }
var j:full; objsize:size; a:adr;
begin j:= popsw - signwd(memw(c));
if (j<0) or (j>memw(c+wsize)) then trap(EARRAY);
objsize := argo(memw(c+wsize+wsize));
a := j*objsize+popa; chkadr(a,objsize);
arraycalc:=a
end;
.ne 20
.sp 2
{---------------------------------------------------------------------------}
{ Double and Real Arithmetic }
{---------------------------------------------------------------------------}
{ All routines for doubles and floats are dummy routines, since the format of
doubles and floats is not defined in EM.
}
function doadi(ds,dt:double):double;
begin { add two doubles } doadi:=0 end;
function dosbi(ds,dt:double):double;
begin { subtract two doubles } dosbi:=0 end;
function domli(ds,dt:double):double;
begin { multiply two doubles } domli:=0 end;
function dodvi(ds,dt:double):double;
begin { divide two doubles } dodvi:=0 end;
function dormi(ds,dt:double):double;
begin { modulo of two doubles } dormi:=0 end;
function dongi(ds:double):double;
begin { negative of a double } dongi:=0 end;
function doadf(x,y:real):real;
begin { add two floats } doadf:=0.0 end;
function dosbf(x,y:real):real;
begin { subtract two floats } dosbf:=0.0 end;
function domlf(x,y:real):real;
begin { multiply two floats } domlf:=0.0 end;
function dodvf(x,y:real):real;
begin { divide two floats } dodvf:=0.0 end;
function dongf(x:real):real;
begin { negate a float } dongf:=0.0 end;
procedure dofif(x,y:real;var intpart,fraction:real);
begin { dismember x*y into integer and fractional parts }
intpart:=0.0; { integer part of x*y, same sign as x*y }
fraction:=0.0;
{ fractional part of x*y, 0<=abs(fraction)<1 and same sign as x*y }
end;
procedure dofef(x:real;var mantissa:real;var exponent:sword);
begin { dismember x into mantissa and exponent parts }
mantissa:=0.0; { mantissa of x , >= 1/2 and <1 }
exponent:=0; { base 2 exponent of x }
end;
.bp
{---------------------------------------------------------------------------}
{ Trap and Call }
{---------------------------------------------------------------------------}
procedure call(p:adr); { Perform the call }
begin
pusha(lb);pusha(pc);
newlb(sp);newsp(sp - memi(pd + pdsize*p + pdlocs));
newpc(memi(pd + pdsize*p+ pdbase))
end;
procedure dotrap(n:byte);
var i:size;
begin
if (uerrorproc=0) or intrap then
begin
if intrap then
writeln('Recursive trap, first trap number was ', trapval:1);
writeln('Error ', n:1);
writeln('With',ord(insr):4,' arg ',k:1);
goto 9999
end;
{ Deposit all interpreter variables that need to be saved on
the stack. This includes all scratch variables that can
be in use at the moment and ( not possible in this interpreter )
the internal address of the interpreter where the error occurred.
This would make it possible to execute an RTT instruction totally
transparent to the user program.
It can, for example, occur within an ADD instruction that both
operands are undefined and that the result overflows.
Although this will generate 3 error traps it must be possible
to ignore them all.
}
intrap:=true; trapval:=n;
for i:=retsize div wsize downto 1 do push(retarea[i]);
push(retsize); { saved return area }
pusha(mema(fileadr)); { saved current file name pointer }
push(memw(lineadr)); { saved line number }
push(n); { push error number }
a:=argp(uerrorproc);
uerrorproc:=0; { reset signal }
call(a); { call the routine }
intrap:=false; { Don't catch recursive traps anymore }
goto 8888; { reenter main loop }
end;
procedure trap;
{ This routine is invoked for overflow, and other run time errors.
For non-fatal errors, trap returns to the calling routine
}
begin
if n>=16 then dotrap(n) else if bit(n,ignmask)=0 then dotrap(n);
end;
procedure dortt;
{ The restoration of file address and line number is not essential.
The restoration of the return save area is.
}
var i:size;
n:word;
begin
newsp(lb); lb:=maxdata+1 ; { to circumvent ESTACK for the popa + pop }
newpc(popa); newlb(popa); { So far a plain RET 0 }
n:=pop; if (n>=16) and (n<64) then goto 9999 ;
lino(pop); filna(popa); retsize:=pop;
for i:=1 to retsize div wsize do retarea[i]:=pop ;
end;
.sp 2
{---------------------------------------------------------------------------}
{ monitor calls }
{---------------------------------------------------------------------------}
procedure domon(entry:word);
var index: 1..63;
dummy: double;
count,rwptr: adr;
token: byte;
i: integer;
begin
if (entry<=0) or (entry>63) then entry:=63 ;
index:=entry;
case index of
1: begin { exit } exitstatus:=pop; halted:=true end;
3: begin { read } dummy:=pop; { All input is from stdin }
rwptr:=popa; count:=popa;
i:=0 ;
while (not eof(input)) and (i<count) do
begin
if eoln(input) then begin storeb(rwptr,10) ; count:=i end
else storeb(rwptr,ord(input^)) ;
get(input); rwptr:=rwptr+1 ; i:=i+1 ;
end;
pusha(i); push(0)
end;
4: begin { write } dummy:=pop; { All output is to stdout }
rwptr:=popa; count:=popa;
for i:=1 to count do
begin token:=memb(rwptr); rwptr:=rwptr+1 ;
if token=10 then writeln else write(chr(token))
end ;
pusha(count);
push(0)
end;
54: begin { ioctl, faked } dummy:=popa;dummy:=popa;dummy:=pop;push(0) end ;
2, 5, 6, 7, 8, 9, 10,
11, 12, 13, 14, 15, 16, 17, 18, 19, 20,
21, 22, 23, 24, 25, 26, 27, 28, 29, 30,
31, 32, 33, 34, 35, 36, 37, 38, 39, 40,
41, 42, 43, 44, 45, 46, 47, 48, 49, 50,
51, 52, 53, 55, 56, 57, 58, 59, 60,
61, 62:
begin push(22); push(22) end;
63: { exists only for the trap }
trap(EBADMON)
end
end;
.bp
{---------------------------------------------------------------------------}
{ Initialization and debugging }
{---------------------------------------------------------------------------}
procedure doident; { print line number and file name }
var a:adr; i,c:integer; found:boolean;
begin
write('at line ',memw(lineadr):1,' ');
a:=mema(fileadr); if a<>0 then
begin i:=20; found:=false;
while (i<>0) and not found do
begin c:=memb(a); a:=a+1; found:=true; i:=i-1;
if (c>=48) and (c<=57) then
begin found:=false; write(chr(ord('0')+c-48)) end;
if (c>=65) and (c<=90) then
begin found:=false; write(chr(ord('A')+c-65)) end;
if (c>=97) and (c<=122) then
begin found:=false; write(chr(ord('a')+c-97)) end;
end;
end;
writeln;
end;
procedure initialize; { start the ball rolling }
{ This is not part of the machine definition }
var cset:set of char;
f:ifset;
iclass:insclass;
insno:byte;
nops:integer;
opcode:byte;
i,j,n:integer;
wtemp:sword;
count:integer;
repc:adr;
nexta,firsta:adr;
elem:byte;
amount,ofst:size;
c:char;
function readb(n:integer):double;
var b:byte;
begin read(prog,b); if n>1 then readb:=readb(n-1)*256+b else readb:=b end;
function readbyte:byte;
begin readbyte:=readb(1) end;
function readword:word;
begin readword:=readb(wsize) end;
function readadr:adr;
begin readadr:=readb(asize) end;
function ifind(ordinal:byte):mnem;
var loopvar:mnem;
found:boolean;
begin ifind:=NON;
loopvar:=insr; found:=false;
repeat
if ordinal=ord(loopvar) then
begin found:=true; ifind:=loopvar end;
if loopvar<>ZRL then loopvar:=succ(loopvar) else loopvar:=NON;
until found or (loopvar=insr) ;
end;
procedure readhdr;
type hdrw=0..32767 ; { 16 bit header words }
var hdr: hdrw;
i: integer;
begin
for i:=0 to 7 do
begin hdr:=readb(2);
case i of
0: if hdr<>3757 then { 07255 }
begin writeln('Not an em load file'); halt end;
2: if hdr<>0 then
begin writeln('Unsolved references'); halt end;
3: if hdr<>3 then
begin writeln('Incorrect load file version'); halt end;
4: if hdr<>wsize then
begin writeln('Incorrect word size'); halt end;
5: if hdr<>asize then
begin writeln('Incorrect pointer size'); halt end;
1,6,7:;
end
end
end;
procedure noinit;
begin writeln('Illegal initialization'); halt end;
procedure readint(a:adr;s:size);
var i:size;
begin { construct integer out of byte sequence }
for i:=1 to s do { construct the value and initialize at a }
begin storeb(a,readbyte); a:=a+1 end
end;
procedure readuns(a:adr;s:size);
begin { construct unsigned out of byte sequence }
readint(a,s) { identical to readint }
end;
procedure readfloat(a:adr;s:size);
var i:size; b:byte;
begin { construct float out of string}
if (s<>4) and (s<>8) then noinit; i:=0;
repeat { eat the bytes, construct the value and intialize at a }
b:=readbyte; i:=i+1;
until b=0 ;
end;
begin
halted:=false;
exitstatus:=undef;
uerrorproc:=0; intrap:=false;
{ initialize tables }
for i:=0 to maxcode do code[i]:=0;
for i:=0 to maxdata do data[i]:=0;
for iclass:=prim to tert do
for i:=0 to 255 do
with dispat[iclass][i] do
begin instr:=NON; iflag:=[zbit] end;
{ read instruction table file. see appendix B }
{ The table read here is a simple transformation of the table on page xx }
{ - instruction names were transformed to numbers }
{ - the '-' flag was transformed to an 'i' flag for 'w' type instructions }
{ - the 'S' flag was added for instructions having signed operands }
reset(tables);
insr:=NON;
repeat
read(tables,insno) ; cset:=[]; f:=[];
insr:=ifind(insno);
if insr=NON then begin writeln('Incorrect table'); halt end;
repeat read(tables,c) until c<>' ' ;
repeat
cset:=cset+[c];
read(tables,c)
until c=' ' ;
if 'm' in cset then f:=f+[mini];
if 's' in cset then f:=f+[short];
if '-' in cset then f:=f+[zbit];
if 'i' in cset then f:=f+[ibit];
if 'S' in cset then f:=f+[sbit];
if 'w' in cset then f:=f+[wbit];
if (mini in f) or (short in f) then read(tables,nops) else nops:=1 ;
readln(tables,opcode);
if ('4' in cset) or ('8' in cset) then
begin iclass:=tert end
else if 'e' in cset then
begin iclass:=second end
else iclass:=prim;
for i:=0 to nops-1 do
begin
with dispat[iclass,opcode+i] do
begin
iflag:=f; instr:=insr;
if '2' in cset then ilength:=2
else if 'u' in cset then ilength:=2
else if '4' in cset then ilength:=4
else if '8' in cset then ilength:=8
else if (mini in f) or (short in f) then
begin
if 'N' in cset then wtemp:=-1-i else wtemp:=i ;
if 'o' in cset then wtemp:=wtemp+1 ;
if short in f then wtemp:=wtemp*256 ;
implicit:=wtemp
end
end
end
until eof(tables);
{ read in program text, data and procedure descriptors }
reset(prog);
readhdr; { verify first header }
for i:=1 to 8 do header[i]:=readadr; { read second header }
hp:=maxdata+1; sp:=maxdata+1; lino(0);
{ read program text }
if header[NTEXT]+header[NPROC]*pdsize>maxcode then
begin writeln('Text size too large'); halt end;
if header[SZDATA]>maxdata then
begin writeln('Data size too large'); halt end;
for i:=0 to header[NTEXT]-1 do code[i]:=readbyte;
{ read data blocks }
nexta:=0;
for i:=1 to header[NDATA] do
begin
n:=readbyte;
if n<>0 then
begin
elem:=readbyte; firsta:=nexta;
case n of
1: { uninitialized words }
for j:=1 to elem do
begin store(nexta,undef); nexta:=nexta+wsize end;
2: { initialized bytes }
for j:=1 to elem do
begin storeb(nexta,readbyte); nexta:=nexta+1 end;
3: { initialized words }
for j:=1 to elem do
begin store(nexta,readword); nexta:=nexta+wsize end;
4,5: { instruction and data pointers }
for j:=1 to elem do
begin storea(nexta,readadr); nexta:=nexta+asize end;
6: { signed integers }
begin readint(nexta,elem); nexta:=nexta+elem end;
7: { unsigned integers }
begin readuns(nexta,elem); nexta:=nexta+elem end;
8: { floating point numbers }
begin readfloat(nexta,elem); nexta:=nexta+elem end;
end
end
else
begin
repc:=readadr; amount:=nexta-firsta;
for count:=1 to repc do
begin
for ofst:=0 to amount-1 do data[nexta+ofst]:=data[firsta+ofst];
nexta:=nexta+amount;
end
end
end;
if header[SZDATA]<>nexta then writeln('Data initialization error');
hp:=nexta;
{ read descriptor table }
pd:=header[NTEXT];
for i:=1 to header[NPROC]*pdsize do code[pd+i-1]:=readbyte;
{ call the entry point routine }
ignmask:=0; { catch all traps, higher numbered traps cannot be ignored}
retsize:=0;
lb:=maxdata; { illegal dynamic link }
pc:=maxcode; { illegal return address }
push(0); a:=sp; { No environment }
push(0); b:=sp; { No args }
pusha(a); { envp }
pusha(b); { argv }
push(0); { argc }
call(argp(header[ENTRY]));
end;
.bp
{---------------------------------------------------------------------------}
{ MAIN LOOP OF THE INTERPRETER }
{---------------------------------------------------------------------------}
{ It should be noted that the interpreter (microprogram) for an EM
machine can be written in two fundamentally different ways: (1) the
instruction operands are fetched in the main loop, or (2) the in-
struction operands are fetched after the 256 way branch, by the exe-
cution routines themselves. In this interpreter, method (1) is used
to simplify the description of execution routines. The dispatch
table dispat is used to determine how the operand is encoded. There
are 4 possibilities:
0. There is no operand
1. The operand and instruction are together in 1 byte (mini)
2. The operand is one byte long and follows the opcode byte(s)
3. The operand is two bytes long and follows the opcode byte(s)
4. The operand is four bytes long and follows the opcode byte(s)
In this interpreter, the main loop determines the operand type,
fetches it, and leaves it in the global variable k for the execution
routines to use. Consequently, instructions such as LOL, which use
three different formats, need only be described once in the body of
the interpreter.
However, for a production interpreter, or a hardware EM
machine, it is probably better to use method (2), i.e. to let the
execution routines themselves fetch their own operands. The reason
for this is that each opcode uniquely determines the operand format,
so no table lookup in the dispatch table is needed. The whole table
is not needed. Method (2) therefore executes much faster.
However, separate execution routines will be needed for LOL with
a one byte offset, and LOL with a two byte offset. It is to avoid
this additional clutter that method (1) is used here. In a produc-
tion interpreter, it is envisioned that the main loop will fetch the
next instruction byte, and use it as an index into a 256 word table
to find the address of the interpreter routine to jump to. The
routine jumped to will begin by fetching its operand, if any,
without any table lookup, since it knows which format to expect.
After doing the work, it returns to the main loop by jumping in-
directly to a register that contains the address of the main loop.
A slight variation on this idea is to have the register contain
the address of the branch table, rather than the address of the main
loop.
Another issue is whether the execution routines for LOL 0, LOL
2, LOL 4, etc. should all be have distinct execution routines. Doing
so provides for the maximum speed, since the operand is implicit in
the routine itself. The disadvantage is that many nearly identical
execution routines will then be needed. Another way of doing it is
to keep the instruction byte fetched from memory (LOL 0, LOL 2, LOL
4, etc.) in some register, and have all the LOL mini format instruc-
tions branch to a common routine. This routine can then determine
the operand by subtracting the code for LOL 0 from the register,
leaving the true operand in the register (as a word quantity of
course). This method makes the interpreter smaller, but is a bit
slower.
.bp
To make this important point a little clearer, consider how a
production interpreter for the PDP-11 might appear. Let us assume the
following opcodes have been assigned:
31: LOL -2 (2 bytes, i.e. next word)
32: LOL -4
33: LOL -6
34: LOL b (format with a one byte offset)
35: LOL w (format with a one word, i.e. two byte offset)
Further assume that each of the 5 opcodes will have its own execution
routine, i.e. we are making a tradeoff in favor of fast execution and
a slightly larger interpreter.
Register r5 is the em program counter.
Register r4 is the em LB register
Register r3 is the em SP register (the stack grows toward low core)
Register r2 contains the interpreter address of the main loop
The main loop looks like this:
movb (r5)+,r0 /fetch the opcode into r0 and increment r5
asl r0 /shift r0 left 1 bit. Now: -256<=r0<=+254
jmp *table(r0) /jump to execution routine
Notice that no operand fetching has been done. The execution routines for
the 5 sample instructions given above might be as follows:
lol2: mov -2(r4),-(sp) /push local -2 onto stack
jmp (r2) /go back to main loop
lol4: mov -4(r4),-(sp) /push local -4 onto stack
jmp (r2) /go back to main loop
lol6: mov -6(r4),-(sp) /push local -6 onto stack
jmp (r2) /go back to main loop
lolb: mov $177400,r0 /prepare to fetch the 1 byte operand
bisb (r5)+,r0 /operand is now in r0
asl r0 /r0 is now offset from LB in bytes, not words
add r4,r0 /r0 is now address of the needed local
mov (r0),-(sp) /push the local onto the stack
jmp (r2)
lolw: clr r0 /prepare to fetch the 2 byte operand
bisb (r5)+,r0 /fetch high order byte first !!!
swab r0 /insert high order byte in place
bisb (r5)+,r0 /insert low order byte in place
asl r0 /convert offset to bytes, from words
add r4,r0 /r0 is now address of needed local
mov (r0),-(sp) /stack the local
jmp (r2) /done
The important thing to notice is where and how the operand fetch occurred:
lol2, lol4, and lol6, (the mini's) have implicit operands
lolb knew it had to fetch one byte, and did so without any table lookup
lolw knew it had to fetch a word, and did so, high order byte first }
.bp
.sp 4
{---------------------------------------------------------------------------}
{ Routines for the individual instructions }
{---------------------------------------------------------------------------}
procedure loadops;
var j:integer;
begin
case insr of
{ LOAD GROUP }
LDC: pushd(argd(k));
LOC: pushsw(argc(k));
LOL: push(memw(locadr(k)));
LOE: push(memw(argg(k)));
LIL: push(memw(mema(locadr(k))));
LOF: push(memw(popa+argf(k)));
LAL: pusha(locadr(k));
LAE: pusha(argg(k));
LXL: begin a:=lb; for j:=1 to argn(k) do a:=mema(a+savsize); pusha(a) end;
LXA: begin a:=lb;
for j:=1 to argn(k) do a:= mema(a+savsize);
pusha(a+savsize)
end;
LOI: pushx(argo(k),popa);
LOS: begin k:=argw(k); if k<>wsize then trap(EILLINS);
k:=pop; pushx(argo(k),popa)
end;
LDL: begin a:=locadr(k); push(memw(a+wsize)); push(memw(a)) end;
LDE: begin k:=argg(k); push(memw(k+wsize)); push(memw(k)) end;
LDF: begin k:=argf(k);
a:=popa; push(memw(a+k+wsize)); push(memw(a+k))
end;
LPI: push(argp(k))
end
end;
procedure storeops;
begin
case insr of
{ STORE GROUP }
STL: store(locadr(k),pop);
STE: store(argg(k),pop);
SIL: store(mema(locadr(k)),pop);
STF: begin a:=popa; store(a+argf(k),pop) end;
STI: popx(argo(k),popa);
STS: begin k:=argw(k); if k<>wsize then trap(EILLINS);
k:=popa; popx(argo(k),popa)
end;
SDL: begin a:=locadr(k); store(a,pop); store(a+wsize,pop) end;
SDE: begin k:=argg(k); store(k,pop); store(k+wsize,pop) end;
SDF: begin k:=argf(k); a:=popa; store(a+k,pop); store(a+k+wsize,pop) end
end
end;
procedure intarith;
var i:integer;
begin
case insr of
{ SIGNED INTEGER ARITHMETIC }
ADI: case szindex(argw(k)) of
1: begin st:=popsw; ss:=popsw; push(fitsw(ss+st,EIOVFL)) end;
2: begin dt:=popd; ds:=popd; pushd(doadi(ds,dt)) end;
end ;
SBI: case szindex(argw(k)) of
1: begin st:=popsw; ss:= popsw; push(fitsw(ss-st,EIOVFL)) end;
2: begin dt:=popd; ds:=popd; pushd(dosbi(ds,dt)) end;
end ;
MLI: case szindex(argw(k)) of
1: begin st:=popsw; ss:= popsw; push(fitsw(ss*st,EIOVFL)) end;
2: begin dt:=popd; ds:=popd; pushd(domli(ds,dt)) end;
end ;
DVI: case szindex(argw(k)) of
1: begin st:= popsw; ss:= popsw;
if st=0 then trap(EIDIVZ) else pushsw(ss div st)
end;
2: begin dt:=popd; ds:=popd; pushd(dodvi(ds,dt)) end;
end;
RMI: case szindex(argw(k)) of
1: begin st:= popsw; ss:=popsw;
if st=0 then trap(EIDIVZ) else pushsw(ss - (ss div st)*st)
end;
2: begin dt:=popd; ds:=popd; pushd(dormi(ds,dt)) end
end;
NGI: case szindex(argw(k)) of
1: begin st:=popsw; pushsw(-st) end;
2: begin ds:=popd; pushd(dongi(ds)) end
end;
SLI: begin t:=pop;
case szindex(argw(k)) of
1: begin ss:=popsw;
for i:= 1 to t do sleft(ss); pushsw(ss)
end
end
end;
SRI: begin t:=pop;
case szindex(argw(k)) of
1: begin ss:=popsw;
for i:= 1 to t do sright(ss); pushsw(ss)
end;
2: begin ds:=popd;
for i:= 1 to t do sdright(ss); pushd(ss)
end
end
end
end
end;
procedure unsarith;
var i:integer;
begin
case insr of
{ UNSIGNED INTEGER ARITHMETIC }
ADU: case szindex(argw(k)) of
1: begin t:=pop; s:= pop; push(chopw(s+t)) end;
2: trap(EILLINS);
end ;
SBU: case szindex(argw(k)) of
1: begin t:=pop; s:= pop; push(chopw(s-t)) end;
2: trap(EILLINS);
end ;
MLU: case szindex(argw(k)) of
1: begin t:=pop; s:= pop; push(chopw(s*t)) end;
2: trap(EILLINS);
end ;
DVU: case szindex(argw(k)) of
1: begin t:= pop; s:= pop;
if t=0 then trap(EIDIVZ) else push(s div t)
end;
2: trap(EILLINS);
end;
RMU: case szindex(argw(k)) of
1: begin t:= pop; s:=pop;
if t=0 then trap(EIDIVZ) else push(s - (s div t)*t)
end;
2: trap(EILLINS);
end;
SLU: case szindex(argw(k)) of
1: begin t:=pop; s:=pop;
for i:= 1 to t do suleft(s); push(s)
end;
2: trap(EILLINS);
end;
SRU: case szindex(argw(k)) of
1: begin t:=pop; s:=pop;
for i:= 1 to t do suright(s); push(s)
end;
2: trap(EILLINS);
end
end
end;
procedure fltarith;
begin
case insr of
{ FLOATING POINT ARITHMETIC }
ADF: begin argwf(k); rt:=popr; rs:=popr; pushr(doadf(rs,rt)) end;
SBF: begin argwf(k); rt:=popr; rs:=popr; pushr(dosbf(rs,rt)) end;
MLF: begin argwf(k); rt:=popr; rs:=popr; pushr(domlf(rs,rt)) end;
DVF: begin argwf(k); rt:=popr; rs:=popr; pushr(dodvf(rs,rt)) end;
NGF: begin argwf(k); rt:=popr; pushr(dongf(rt)) end;
FIF: begin argwf(k); rt:=popr; rs:=popr;
dofif(rt,rs,x,y); pushr(y); pushr(x)
end;
FEF: begin argwf(k); rt:=popr; dofef(rt,x,ss); pushr(x); pushsw(ss) end
end
end;
procedure ptrarith;
begin
case insr of
{ POINTER ARITHMETIC }
ADP: pusha(popa+argf(k));
ADS: case szindex(argw(k)) of
1: begin st:=popsw; pusha(popa+st) end;
2: begin dt:=popd; pusha(popa+dt) end;
end;
SBS: begin
a:=popa; b:=popa;
case szindex(argw(k)) of
1: push(fitsw(b-a,EIOVFL));
2: pushd(b-a)
end
end
end
end;
procedure incops;
var j:integer;
begin
case insr of
{ INCREMENT/DECREMENT/ZERO }
INC: push(fitsw(popsw+1,EIOVFL));
INL: begin a:=locadr(k); store(a,fitsw(signwd(memw(a))+1,EIOVFL)) end;
INE: begin a:=argg(k); store(a,fitsw(signwd(memw(a))+1,EIOVFL)) end;
DEC: push(fitsw(popsw-1,EIOVFL));
DEL: begin a:=locadr(k); store(a,fitsw(signwd(memw(a))-1,EIOVFL)) end;
DEE: begin a:=argg(k); store(a,fitsw(signwd(memw(a))-1,EIOVFL)) end;
ZRL: store(locadr(k),0);
ZRE: store(argg(k),0);
ZER: for j:=1 to argw(k) div wsize do push(0);
ZRF: pushr(0);
end
end;
procedure convops;
begin
case insr of
{ CONVERT GROUP }
CII: begin s:=pop; t:=pop;
if t<wsize then begin push(sextend(pop,t)); t:=wsize end;
case szindex(argw(t)) of
1: if szindex(argw(s))=2 then pushd(popsw);
2: if szindex(argw(s))=1 then push(fitsw(popd,ECONV))
end
end;
CIU: case szindex(argw(pop)) of
1: if szindex(argw(pop))=2 then push(unsign(popd mod negoff));
2: trap(EILLINS);
end;
CIF: begin argwf(pop);
case szindex(argw(pop)) of 1:pushr(popsw); 2:pushr(popd) end
end;
CUI: case szindex(argw(pop)) of
1: case szindex(argw(pop)) of
1: begin s:=pop; if s>maxsint then trap(ECONV); push(s) end;
2: trap(EILLINS);
end;
2: case szindex(argw(pop)) of
1: pushd(pop);
2: trap(EILLINS);
end;
end;
CUU: case szindex(argw(pop)) of
1: if szindex(argw(pop))=2 then trap(EILLINS);
2: trap(EILLINS);
end;
CUF: begin argwf(pop);
if szindex(argw(pop))=1 then pushr(pop) else trap(EILLINS)
end;
CFI: begin sz:=argw(pop); argwf(pop); rt:=popr;
case szindex(sz) of
1: push(fitsw(trunc(rt),ECONV));
2: pushd(fitd(trunc(rt)));
end
end;
CFU: begin sz:=argw(pop); argwf(pop); rt:=popr;
case szindex(sz) of
1: push( chopw(trunc(abs(rt)-0.5)) );
2: trap(EILLINS);
end
end;
CFF: begin argwf(pop); argwf(pop) end
end
end;
procedure logops;
var i,j:integer;
begin
case insr of
{ LOGICAL GROUP }
XAND:
begin k:=argw(k);
for j:= 1 to k div wsize do
begin a:=sp+k; t:=pop; store(a,bf(andf,memw(a),t)) end;
end;
IOR:
begin k:=argw(k);
for j:= 1 to k div wsize do
begin a:=sp+k; t:=pop; store(a,bf(iorf,memw(a),t)) end;
end;
XOR:
begin k:=argw(k);
for j:= 1 to k div wsize do
begin a:=sp+k; t:=pop; store(a,bf(xorf,memw(a),t)) end;
end;
COM:
begin k:=argw(k);
for j:= 1 to k div wsize do
begin
store(sp+k-wsize*j, bf(xorf,memw(sp+k-wsize*j), negoff-1))
end
end;
ROL: begin k:=argw(k); if k<>wsize then trap(EILLINS);
t:=pop; s:=pop; for i:= 1 to t do rleft(s); push(s)
end;
ROR: begin k:=argw(k); if k<>wsize then trap(EILLINS);
t:=pop; s:=pop; for i:= 1 to t do rright(s); push(s)
end
end
end;
procedure setops;
var i,j:integer;
begin
case insr of
{ SET GROUP }
INN:
begin k:=argw(k);
t:=pop;
i:= t mod 8; t:= t div 8;
if t>=k then
begin trap(ESET); s:=0 end
else
begin s:=memb(sp+t) end;
newsp(sp+k); push(bit(i,s));
end;
XSET:
begin k:=argw(k);
t:=pop;
i:= t mod 8; t:= t div 8;
for j:= 1 to k div wsize do push(0);
if t>=k then
trap(ESET)
else
begin s:=1; for j:= 1 to i do rleft(s); storeb(sp+t,s) end
end
end
end;
procedure arrops;
begin
case insr of
{ ARRAY GROUP }
LAR:
begin k:=argw(k); if k<>wsize then trap(EILLINS); a:=popa;
pushx(argo(memw(a+2*k)),arraycalc(a))
end;
SAR:
begin k:=argw(k); if k<>wsize then trap(EILLINS); a:=popa;
popx(argo(memw(a+2*k)),arraycalc(a))
end;
AAR:
begin k:=argw(k); if k<>wsize then trap(EILLINS); a:=popa;
push(arraycalc(a))
end
end
end;
procedure cmpops;
begin
case insr of
{ COMPARE GROUP }
CMI: case szindex(argw(k)) of
1: begin st:=popsw; ss:=popsw;
if ss<st then pushsw(-1) else if ss=st then push(0) else push(1)
end;
2: begin dt:=popd; ds:=popd;
if ds<dt then pushsw(-1) else if ds=dt then push(0) else push(1)
end;
end;
CMU: case szindex(argw(k)) of
1: begin t:=pop; s:=pop;
if s<t then pushsw(-1) else if s=t then push(0) else push(1)
end;
2: trap(EILLINS);
end;
CMP: begin a:=popa; b:=popa;
if b<a then pushsw(-1) else if b=a then push(0) else push(1)
end;
CMF: begin argwf(k); rt:=popr; rs:=popr;
if rs<rt then pushsw(-1) else if rs=rt then push(0) else push(1)
end;
CMS: begin k:=argw(k);
t:= 0; j:= 0;
while (j < k) and (t=0) do
begin if memw(sp+j) <> memw(sp+k+j) then t:=1;
j:=j+wsize
end;
newsp(sp+wsize*k); push(t);
end;
TLT: if popsw < 0 then push(1) else push(0);
TLE: if popsw <= 0 then push(1) else push(0);
TEQ: if pop = 0 then push(1) else push(0);
TNE: if pop <> 0 then push(1) else push(0);
TGE: if popsw >= 0 then push(1) else push(0);
TGT: if popsw > 0 then push(1) else push(0);
end
end;
procedure branchops;
begin
case insr of
{ BRANCH GROUP }
BRA: newpc(pc+k);
BLT: begin st:=popsw; if popsw < st then newpc(pc+k) end;
BLE: begin st:=popsw; if popsw <= st then newpc(pc+k) end;
BEQ: begin t :=pop ; if pop = t then newpc(pc+k) end;
BNE: begin t :=pop ; if pop <> t then newpc(pc+k) end;
BGE: begin st:=popsw; if popsw >= st then newpc(pc+k) end;
BGT: begin st:=popsw; if popsw > st then newpc(pc+k) end;
ZLT: if popsw < 0 then newpc(pc+k);
ZLE: if popsw <= 0 then newpc(pc+k);
ZEQ: if pop = 0 then newpc(pc+k);
ZNE: if pop <> 0 then newpc(pc+k);
ZGE: if popsw >= 0 then newpc(pc+k);
ZGT: if popsw > 0 then newpc(pc+k)
end
end;
procedure callops;
var j:integer;
begin
case insr of
{ PROCEDURE CALL GROUP }
CAL: call(argp(k));
CAI: begin call(argp(popa)) end;
RET: begin k:=argz(k); if k div wsize>maxret then trap(EILLINS);
for j:= 1 to k div wsize do retarea[j]:=pop; retsize:=k;
newsp(lb); lb:=maxdata+1; { To circumvent stack overflow error }
newpc(popa);
if pc=maxcode then
begin
halted:=true;
if retsize=wsize then exitstatus:=retarea[1]
else exitstatus:=undef
end
else
newlb(popa);
end;
LFR: begin k:=args(k); if k<>retsize then trap(EILLINS);
for j:=k div wsize downto 1 do push(retarea[j]);
end
end
end;
procedure miscops;
var i,j:integer;
begin
case insr of
{ MISCELLANEOUS GROUP }
ASP,ASS:
begin if insr=ASS then
begin k:=argw(k); if k<>wsize then trap(EILLINS); k:=popsw end;
k:=argf(k);
if k<0
then for j:= 1 to -k div wsize do push(undef)
else newsp(sp+k);
end;
BLM,BLS:
begin if insr=BLS then
begin k:=argw(k); if k<>wsize then trap(EILLINS); k:=pop end;
k:=argz(k);
b:=popa; a:=popa;
for j := 1 to k div wsize do
store(b-wsize+wsize*j,memw(a-wsize+wsize*j))
end;
CSA: begin k:=argw(k); if k<>wsize then trap(EILLINS);
a:=popa;
st:= popsw - signwd(memw(a+asize));
if (st>=0) and (st<=memw(a+wsize+asize)) then
b:=mema(a+2*wsize+asize+asize*st) else b:=mema(a);
if b=0 then trap(ECASE) else newpc(b)
end;
CSB: begin k:=argw(k); if k<>wsize then trap(EILLINS); a:=popa;
t:=pop; i:=1; found:=false;
while (i<=memw(a+asize)) and not found do
if t=memw(a+(asize+wsize)*i) then found:=true else i:=i+1;
if found then b:=memw(a+(asize+wsize)*i+wsize) else b:=memw(a);
if b=0 then trap(ECASE) else newpc(b);
end;
DCH: begin pusha(mema(popa+dynd)) end;
DUP,DUS:
begin if insr=DUS then
begin k:=argw(k); if k<>wsize then trap(EILLINS); k:=pop end;
k:=args(k);
for i:=1 to k div wsize do push(memw(sp+k-wsize));
end;
EXG: begin
k:=argw(k);
for i:=1 to k div wsize do push(memw(sp+k-wsize));
for i:=0 to k div wsize - 1 do
store(sp+k+i*wsize,memw(sp+k+k+i*wsize));
for i:=1 to k div wsize do
begin t:=pop ; store(sp+k+k-wsize,t) end;
end;
FIL: filna(argg(k));
GTO: begin k:=argg(k);
newlb(mema(k+2*asize)); newsp(mema(k+asize)); newpc(mema(k))
end;
LIM: push(ignmask);
LIN: lino(argn(k));
LNI: lino(memw(0)+1);
LOR: begin i:=argr(k);
case i of 0:pusha(lb); 1:pusha(sp); 2:pusha(hp) end;
end;
LPB: pusha(popa+statd);
MON: domon(pop);
NOP: writeln('NOP at line ',memw(0):5) ;
RCK: begin a:=popa;
case szindex(argw(k)) of
1: if (signwd(memw(sp))<signwd(memw(a))) or
(signwd(memw(sp))>signwd(memw(a+wsize))) then trap(ERANGE);
2: if (memd(sp)<memd(a)) or
(memd(sp)>memd(a+2*wsize)) then trap(ERANGE);
end
end;
RTT: dortt;
SIG: begin a:=popa; pusha(uerrorproc); uerrorproc:=a end;
SIM: ignmask:=pop;
STR: begin i:=argr(k);
case i of 0: newlb(popa); 1: newsp(popa); 2: newhp(popa) end;
end;
TRP: trap(pop)
end
end;
.bp
{---------------------------------------------------------------------------}
{ Main Loop }
{---------------------------------------------------------------------------}
begin initialize;
8888:
repeat
opcode := nextpc; { fetch the first byte of the instruction }
if opcode=escape1 then iclass:=second
else if opcode=escape2 then iclass:=tert
else iclass:=prim;
if iclass<>prim then opcode := nextpc;
with dispat[iclass][opcode] do
begin insr:=instr;
if not (zbit in iflag) then
if ibit in iflag then k:=pop else
begin
if mini in iflag then k:=implicit else
begin
if short in iflag then k:=implicit+nextpc else
begin k:=nextpc;
if (sbit in iflag) and (k>=128) then k:=k-256;
for i:=2 to ilength do k:=256*k + nextpc
end
end;
if wbit in iflag then k:=k*wsize;
end
end;
case insr of
NON: trap(EILLINS);
{ LOAD GROUP }
LDC,LOC,LOL,LOE,LIL,LOF,LAL,LAE,LXL,LXA,LOI,LOS,LDL,LDE,LDF,LPI:
loadops;
{ STORE GROUP }
STL,STE,SIL,STF,STI,STS,SDL,SDE,SDF:
storeops;
{ SIGNED INTEGER ARITHMETIC }
ADI,SBI,MLI,DVI,RMI,NGI,SLI,SRI:
intarith;
{ UNSIGNED INTEGER ARITHMETIC }
ADU,SBU,MLU,DVU,RMU,SLU,SRU:
unsarith;
{ FLOATING POINT ARITHMETIC }
ADF,SBF,MLF,DVF,NGF,FIF,FEF:
fltarith;
{ POINTER ARITHMETIC }
ADP,ADS,SBS:
ptrarith;
{ INCREMENT/DECREMENT/ZERO }
INC,INL,INE,DEC,DEL,DEE,ZRL,ZRE,ZER,ZRF:
incops;
{ CONVERT GROUP }
CII,CIU,CIF,CUI,CUU,CUF,CFI,CFU,CFF:
convops;
{ LOGICAL GROUP }
XAND,IOR,XOR,COM,ROL,ROR:
logops;
{ SET GROUP }
INN,XSET:
setops;
{ ARRAY GROUP }
LAR,SAR,AAR:
arrops;
{ COMPARE GROUP }
CMI,CMU,CMP,CMF,CMS, TLT,TLE,TEQ,TNE,TGE,TGT:
cmpops;
{ BRANCH GROUP }
BRA, BLT,BLE,BEQ,BNE,BGE,BGT, ZLT,ZLE,ZEQ,ZNE,ZGE,ZGT:
branchops;
{ PROCEDURE CALL GROUP }
CAL,CAI,RET,LFR:
callops;
{ MISCELLANEOUS GROUP }
ASP,ASS,BLM,BLS,CSA,CSB,DCH,DUP,DUS,EXG,FIL,GTO,LIM,
LIN,LNI,LOR,LPB,MON,NOP,RCK,RTT,SIG,SIM,STR,TRP:
miscops;
end; { end of case statement }
if not ( (insr=RET) or (insr=ASP) or (insr=BRA) or (insr=GTO) ) then
retsize:=0 ;
until halted;
9999:
writeln('halt with exit status: ',exitstatus:1);
doident;
end.
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