File:  [gforth] / gforth / kernel / cond.fs
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Mon Jan 20 17:07:41 2003 UTC (19 years, 10 months ago) by anton
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undid changes to copyright notices

    1: \ Structural Conditionals                              12dec92py
    2: 
    3: \ Copyright (C) 1995,1996,1997,2000 Free Software Foundation, Inc.
    4: 
    5: \ This file is part of Gforth.
    6: 
    7: \ Gforth is free software; you can redistribute it and/or
    8: \ modify it under the terms of the GNU General Public License
    9: \ as published by the Free Software Foundation; either version 2
   10: \ of the License, or (at your option) any later version.
   11: 
   12: \ This program is distributed in the hope that it will be useful,
   13: \ but WITHOUT ANY WARRANTY; without even the implied warranty of
   14: \ MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   15: \ GNU General Public License for more details.
   16: 
   17: \ You should have received a copy of the GNU General Public License
   18: \ along with this program; if not, write to the Free Software
   19: \ Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111, USA.
   20: 
   21: here 0 , \ just a dummy, the real value of locals-list is patched into it in glocals.fs
   22: AConstant locals-list \ acts like a variable that contains
   23: 		      \ a linear list of locals names
   24: 
   25: 
   26: variable dead-code \ true if normal code at "here" would be dead
   27: variable backedge-locals
   28:     \ contains the locals list that BEGIN will assume to be live on
   29:     \ the back edge if the BEGIN is unreachable from above. Set by
   30:     \ ASSUME-LIVE, reset by UNREACHABLE.
   31: 
   32: : UNREACHABLE ( -- ) \ gforth
   33:     \ declares the current point of execution as unreachable
   34:     dead-code on
   35:     0 backedge-locals ! ; immediate
   36: 
   37: : ASSUME-LIVE ( orig -- orig ) \ gforth
   38:     \ used immediatly before a BEGIN that is not reachable from
   39:     \ above.  causes the BEGIN to assume that the same locals are live
   40:     \ as at the orig point
   41:     dup orig?
   42:     2 pick backedge-locals ! ; immediate
   43:     
   44: \ Control Flow Stack
   45: \ orig, etc. have the following structure:
   46: \ type ( defstart, live-orig, dead-orig, dest, do-dest, scopestart) ( TOS )
   47: \ address (of the branch or the instruction to be branched to) (second)
   48: \ locals-list (valid at address) (third)
   49: 
   50: \ types
   51: [IFUNDEF] defstart 
   52: 0 constant defstart	\ usally defined in comp.fs
   53: [THEN]
   54: 1 constant live-orig
   55: 2 constant dead-orig
   56: 3 constant dest \ the loopback branch is always assumed live
   57: 4 constant do-dest
   58: 5 constant scopestart
   59: 
   60: : def? ( n -- )
   61:     defstart <> abort" unstructured " ;
   62: 
   63: : orig? ( n -- )
   64:  dup live-orig <> swap dead-orig <> and abort" expected orig " ;
   65: 
   66: : dest? ( n -- )
   67:  dest <> abort" expected dest " ;
   68: 
   69: : do-dest? ( n -- )
   70:  do-dest <> abort" expected do-dest " ;
   71: 
   72: : scope? ( n -- )
   73:  scopestart <> abort" expected scope " ;
   74: 
   75: : non-orig? ( n -- )
   76:  dest scopestart 1+ within 0= abort" expected dest, do-dest or scope" ;
   77: 
   78: : cs-item? ( n -- )
   79:  live-orig scopestart 1+ within 0= abort" expected control flow stack item" ;
   80: 
   81: 3 constant cs-item-size
   82: 
   83: : CS-PICK ( ... u -- ... destu ) \ tools-ext c-s-pick
   84:  1+ cs-item-size * 1- >r
   85:  r@ pick  r@ pick  r@ pick
   86:  rdrop
   87:  dup non-orig? ;
   88: 
   89: : CS-ROLL ( destu/origu .. dest0/orig0 u -- .. dest0/orig0 destu/origu ) \ tools-ext c-s-roll
   90:  1+ cs-item-size * 1- >r
   91:  r@ roll r@ roll r@ roll
   92:  rdrop
   93:  dup cs-item? ; 
   94: 
   95: : cs-push-part ( -- list addr )
   96:  locals-list @ here ;
   97: 
   98: : cs-push-orig ( -- orig )
   99:  cs-push-part dead-code @
  100:  if
  101:    dead-orig
  102:  else
  103:    live-orig
  104:  then ;   
  105: 
  106: \ Structural Conditionals                              12dec92py
  107: 
  108: : ?struc      ( flag -- )       abort" unstructured " ;
  109: : sys?        ( sys -- )        dup 0= ?struc ;
  110: : >mark ( -- orig )
  111:  cs-push-orig 0 , ;
  112: : >resolve    ( addr -- )
  113:     here swap !
  114:     basic-block-end ;
  115: : <resolve    ( addr -- )        , ;
  116: 
  117: : BUT
  118:     1 cs-roll ;                      immediate restrict
  119: : YET
  120:     0 cs-pick ;                       immediate restrict
  121: 
  122: \ Structural Conditionals                              12dec92py
  123: 
  124: : AHEAD ( compilation -- orig ; run-time -- ) \ tools-ext
  125:     POSTPONE branch  >mark  POSTPONE unreachable ; immediate restrict
  126: 
  127: : IF ( compilation -- orig ; run-time f -- ) \ core
  128:  POSTPONE ?branch >mark ; immediate restrict
  129: 
  130: : ?DUP-IF ( compilation -- orig ; run-time n -- n| ) \ gforth	question-dupe-if
  131: \G This is the preferred alternative to the idiom "@code{?DUP IF}", since it can be
  132: \G better handled by tools like stack checkers. Besides, it's faster.
  133:     POSTPONE ?dup-?branch >mark ;       immediate restrict
  134: 
  135: : ?DUP-0=-IF ( compilation -- orig ; run-time n -- n| ) \ gforth	question-dupe-zero-equals-if
  136:     POSTPONE ?dup-0=-?branch >mark ;       immediate restrict
  137: 
  138: Defer then-like ( orig -- )
  139: : cs>addr ( orig/dest -- )  drop >resolve drop ;
  140: ' cs>addr IS then-like
  141: 
  142: : THEN ( compilation orig -- ; run-time -- ) \ core
  143:     dup orig?  then-like ; immediate restrict
  144: 
  145: ' THEN alias ENDIF ( compilation orig -- ; run-time -- ) \ gforth
  146: immediate restrict
  147: \ Same as "THEN". This is what you use if your program will be seen by
  148: \ people who have not been brought up with Forth (or who have been
  149: \ brought up with fig-Forth).
  150: 
  151: : ELSE ( compilation orig1 -- orig2 ; run-time f -- ) \ core
  152:     POSTPONE ahead
  153:     1 cs-roll
  154:     POSTPONE then ; immediate restrict
  155: 
  156: Defer begin-like ( -- )
  157: ' noop IS begin-like
  158: 
  159: : BEGIN ( compilation -- dest ; run-time -- ) \ core
  160:     begin-like cs-push-part dest
  161:     basic-block-end ; immediate restrict
  162: 
  163: Defer again-like ( dest -- addr )
  164: ' nip IS again-like
  165: 
  166: : AGAIN ( compilation dest -- ; run-time -- ) \ core-ext
  167:     dest? again-like  POSTPONE branch  <resolve ; immediate restrict
  168: 
  169: Defer until-like ( list addr xt1 xt2 -- )
  170: :noname ( list addr xt1 xt2 -- )
  171:     drop compile, <resolve drop ;
  172: IS until-like
  173: 
  174: : UNTIL ( compilation dest -- ; run-time f -- ) \ core
  175:     dest? ['] ?branch ['] ?branch-lp+!# until-like ; immediate restrict
  176: 
  177: : WHILE ( compilation dest -- orig dest ; run-time f -- ) \ core
  178:     POSTPONE if
  179:     1 cs-roll ; immediate restrict
  180: 
  181: : REPEAT ( compilation orig dest -- ; run-time -- ) \ core
  182:     POSTPONE again
  183:     POSTPONE then ; immediate restrict
  184: 
  185: \ counted loops
  186: 
  187: \ leave poses a little problem here
  188: \ we have to store more than just the address of the branch, so the
  189: \ traditional linked list approach is no longer viable.
  190: \ This is solved by storing the information about the leavings in a
  191: \ special stack.
  192: 
  193: \ !! remove the fixed size limit. 'Tis not hard.
  194: 20 constant leave-stack-size
  195: create leave-stack  60 cells allot
  196: Avariable leave-sp  leave-stack 3 cells + leave-sp !
  197: 
  198: : clear-leave-stack ( -- )
  199:     leave-stack leave-sp ! ;
  200: 
  201: \ : leave-empty? ( -- f )
  202: \  leave-sp @ leave-stack = ;
  203: 
  204: : >leave ( orig -- )
  205:     \ push on leave-stack
  206:     leave-sp @
  207:     dup [ leave-stack 60 cells + ] Aliteral
  208:     >= abort" leave-stack full"
  209:     tuck ! cell+
  210:     tuck ! cell+
  211:     tuck ! cell+
  212:     leave-sp ! ;
  213: 
  214: : leave> ( -- orig )
  215:     \ pop from leave-stack
  216:     leave-sp @
  217:     dup leave-stack <= IF
  218:        drop 0 0 0  EXIT  THEN
  219:     cell - dup @ swap
  220:     cell - dup @ swap
  221:     cell - dup @ swap
  222:     leave-sp ! ;
  223: 
  224: : DONE ( compilation orig -- ; run-time -- ) \ gforth
  225:     \ !! the original done had ( addr -- )
  226:     drop >r drop
  227:     begin
  228: 	leave>
  229: 	over r@ u>=
  230:     while
  231: 	POSTPONE then
  232:     repeat
  233:     >leave rdrop ; immediate restrict
  234: 
  235: : LEAVE ( compilation -- ; run-time loop-sys -- ) \ core
  236:     POSTPONE ahead
  237:     >leave ; immediate restrict
  238: 
  239: : ?LEAVE ( compilation -- ; run-time f | f loop-sys -- ) \ gforth	question-leave
  240:     POSTPONE 0= POSTPONE if
  241:     >leave ; immediate restrict
  242: 
  243: : DO ( compilation -- do-sys ; run-time w1 w2 -- loop-sys ) \ core
  244:     POSTPONE (do)
  245:     POSTPONE begin drop do-dest
  246:     ( 0 0 0 >leave ) ; immediate restrict
  247: 
  248: : ?do-like ( -- do-sys )
  249:     ( 0 0 0 >leave )
  250:     >mark >leave
  251:     POSTPONE begin drop do-dest ;
  252: 
  253: : ?DO ( compilation -- do-sys ; run-time w1 w2 -- | loop-sys )	\ core-ext	question-do
  254:     POSTPONE (?do) ?do-like ; immediate restrict
  255: 
  256: : +DO ( compilation -- do-sys ; run-time n1 n2 -- | loop-sys )	\ gforth	plus-do
  257:     POSTPONE (+do) ?do-like ; immediate restrict
  258: 
  259: : U+DO ( compilation -- do-sys ; run-time u1 u2 -- | loop-sys )	\ gforth	u-plus-do
  260:     POSTPONE (u+do) ?do-like ; immediate restrict
  261: 
  262: : -DO ( compilation -- do-sys ; run-time n1 n2 -- | loop-sys )	\ gforth	minus-do
  263:     POSTPONE (-do) ?do-like ; immediate restrict
  264: 
  265: : U-DO ( compilation -- do-sys ; run-time u1 u2 -- | loop-sys )	\ gforth	u-minus-do
  266:     POSTPONE (u-do) ?do-like ; immediate restrict
  267: 
  268: : FOR ( compilation -- do-sys ; run-time u -- loop-sys )	\ gforth
  269:     POSTPONE (for)
  270:     POSTPONE begin drop do-dest
  271:     ( 0 0 0 >leave ) ; immediate restrict
  272: 
  273: \ LOOP etc. are just like UNTIL
  274: 
  275: : loop-like ( do-sys xt1 xt2 -- )
  276:     >r >r 0 cs-pick swap cell - swap 1 cs-roll r> r> rot do-dest?
  277:     until-like  POSTPONE done  POSTPONE unloop ;
  278: 
  279: : LOOP ( compilation do-sys -- ; run-time loop-sys1 -- | loop-sys2 )	\ core
  280:  ['] (loop) ['] (loop)-lp+!# loop-like ; immediate restrict
  281: 
  282: : +LOOP ( compilation do-sys -- ; run-time loop-sys1 n -- | loop-sys2 )	\ core	plus-loop
  283:  ['] (+loop) ['] (+loop)-lp+!# loop-like ; immediate restrict
  284: 
  285: \ !! should the compiler warn about +DO..-LOOP?
  286: : -LOOP ( compilation do-sys -- ; run-time loop-sys1 u -- | loop-sys2 )	\ gforth	minus-loop
  287:  ['] (-loop) ['] (-loop)-lp+!# loop-like ; immediate restrict
  288: 
  289: \ A symmetric version of "+LOOP". I.e., "-high -low ?DO -inc S+LOOP"
  290: \ will iterate as often as "high low ?DO inc S+LOOP". For positive
  291: \ increments it behaves like "+LOOP". Use S+LOOP instead of +LOOP for
  292: \ negative increments.
  293: : S+LOOP ( compilation do-sys -- ; run-time loop-sys1 n -- | loop-sys2 )	\ gforth	s-plus-loop
  294:  ['] (s+loop) ['] (s+loop)-lp+!# loop-like ; immediate restrict
  295: 
  296: : NEXT ( compilation do-sys -- ; run-time loop-sys1 -- | loop-sys2 ) \ gforth
  297:  ['] (next) ['] (next)-lp+!# loop-like ; immediate restrict
  298: 
  299: \ Structural Conditionals                              12dec92py
  300: 
  301: Defer exit-like ( -- )
  302: ' noop IS exit-like
  303: 
  304: : EXIT ( compilation -- ; run-time nest-sys -- ) \ core
  305: \G Return to the calling definition; usually used as a way of
  306: \G forcing an early return from a definition. Before
  307: \G @code{EXIT}ing you must clean up the return stack and
  308: \G @code{UNLOOP} any outstanding @code{?DO}...@code{LOOP}s.
  309:     exit-like
  310:     POSTPONE ;s
  311:     basic-block-end
  312:     POSTPONE unreachable ; immediate restrict
  313: 
  314: : ?EXIT ( -- ) ( compilation -- ; run-time nest-sys f -- | nest-sys ) \ gforth
  315:      POSTPONE if POSTPONE exit POSTPONE then ; immediate restrict
  316: 

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