.bp .AP "EM INTERPRETER" .nf .ft CW .lg 0 .nr x \w' ' .ta \nxu +\nxu +\nxu +\nxu +\nxu +\nxu +\nxu +\nxu +\nxu +\nxu { 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 instruction number } 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=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 s0 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 (a0) then trap(ESTACK); sp:=a end; procedure newlb(a:adr); begin if (a0) 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) else 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= 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 (i0 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 tmaxsint 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 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+wsize))) then trap(ERANGE); 2: if (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. .ft P .lg 1 .fi