The Atari Compendium/The Atari Compendium (Toad Computers) (1994).iso/files/prgtools/editors/mutt/me2s_pl7.zoo/mu_edit2/mc2/control.c

C/C++ Source or Header | 1992-08-26 | 4.6 KB | 186 lines

/* control.c : Compile control structures like while, for next, etc.
 * Return: class
 */

/* Copyright 1990, 1991, 1992 Craig Durland
 *   Distributed under the terms of the GNU General Public License.
 *   Distributed "as is", without warranties of any kind, but comments,
 *     suggestions and bug reports are welcome.
 */

#include <os.h>
#include "mc.h"
#include "mm.h"
#include "opcode.h"

extern char token[];

extern int
    breaklabel, contlabel,        /* in mc.c */
    btv;
extern unsigned int class;        /* in mc.c */

    /* (while (test)(body))
     * Compiles down to:
     *   1: if (test) is FALSE goto 2    ; ignore if (test) ==TRUE
     *    (body)
     *    goto 1
     *   2:
     */
comp_while()
{
  int l1, ldone, savebl = breaklabel, savecl = contlabel,z;

  l1 = contlabel = genlabel(); ldone = breaklabel = genlabel();
  stufflabel(l1);
  lookahead();            /* check for TRUE or FALSE */
  if (class == BOOLEAN)
  {
    if (btv == FALSE)        /* (while FALSE (body) */
    {
      groan("while loop never executed.");
      gojmp(JMP,ldone);
    }
    get_token();
  }
  else                /* compile (test) */
    { compile(); type_check(BOOLEAN,0); gojmp(JMPFALSE,ldone); }
  compile(); z = class;        /* compile (body), save result */
  gojmp(JMP,l1);        /* jump back to (test) */
  stufflabel(ldone);        /* next address after (body) */
  breaklabel = savebl; contlabel = savecl;
      /* If we did a (push-arg) and we are compiling args for a fcn
       *   call, don't push RV.
       * Else we don't know what RV is because of possible
       *   (break)
       */
  return (z == PUSHEDARGS) ? PUSHEDARGS : UNKNOWN;
}

    /* (for (init)(test)(inc)(body)) : a glorified while
     * Compiles down to:
     *    (init)
     *   1: if (test) is FALSE goto 3
     *    (goto 2)
     *    (inc)
     *   2: (body)
     *    (goto 1)
     *   3:
     */
comp_for()
{
  int l1, l2, savebl = breaklabel, savecl = contlabel, z;

  l1 = genlabel(); contlabel = genlabel(); l2 = genlabel();
  breaklabel = genlabel();
  compile();                /* (init) */
  stufflabel(l1);            /* (test) */
  compile(); type_check(BOOLEAN,0); gojmp(JMPFALSE,breaklabel);
  gojmp(JMP,l2);            /* jmp around (inc) */
  stufflabel(contlabel); compile(); gojmp(JMP,l1);         /* (inc) */
  stufflabel(l2); compile(); z = class; gojmp(JMP,contlabel);     /* (body) */
  stufflabel(breaklabel);
  breaklabel = savebl; contlabel = savecl;
  return (z == PUSHEDARGS) ? PUSHEDARGS : UNKNOWN;    /* same as (while) */
}

    /* (if (test) (t) (f))
     * Compiles down to:
     *    if (test) is FALSE goto 1
     *    (t)
     *    goto 2        ; not used if no else clause
     *   1: (f)        ; not used if no else clause
     *   2:            ; not used if no else clause
     * Note:
     *   (if () ...) means use RV for the test.
     */
comp_if(lastclass) unsigned int lastclass;
{
  int l1, l2, z;

  l1 = genlabel();
  compile(); if (class == EMPTY) class = lastclass;
  type_check(BOOLEAN,0); gojmp(JMPFALSE,l1);
  compile(); z = class;
  lookahead();                /* check for else block */
  if (class == DELIMITER && *token == ')') stufflabel(l1);
  else
  {
    l2 = genlabel();
    gojmp(JMP,l2); stufflabel(l1);
    compile(); if (z != class) z = UNKNOWN;
    stufflabel(l2);
  }
  return z;
}

    /* (cond (test1) (body1) (test2) (body2) ...)
     * A glorified if then else if then else if then else ...
     * Compiles down to:
     *    if (test1) is FALSE goto 2
     *    (body1)
     *    goto done
     *   2: if (test2) is FALSE goto 3
     *    (body2)
     *    goto done
     *   3:
     *   done:
     */
comp_cond()
{
  int l1, ldone;

  ldone = genlabel();
  do
  {
    l1 = genlabel();
    compile(); type_check(BOOLEAN,0); gojmp(JMPFALSE,l1);
    compile(); gojmp(JMP,ldone);
    stufflabel(l1);
  }
  while (gaze_ahead(BOOLEAN,0));
  stufflabel(ldone);
  return UNKNOWN;
}

    /* (switch val  val1 (body1) val2 (body2) ... [default (dbody)])
     * A simplified if then else if then else if then else
     * Compiles down to:
     *    push val
     *    if val1 != val goto 2
     *    body1
     *    goto done
     *   2: if val2 != val goto 3
     *    body2
     *    goto done
     *   3:  ...
     *    (dbody)        ; the default case
     *   done: pop val
     */
comp_switch()
{
  int l1, ldone, z;

  ldone = genlabel();
  compile(); z = class;
  checkit("switch",STRING,NUMBER,BOOLEAN,0);
  pushpush();
  do
  {
    lookahead();
    if (class == TOKEN && strcmp(token,"default") == 0)
      { get_token(); compile(); break; }
    else
    {
      l1 = genlabel();
      genop(DUP); compile();
      if (z != UNKNOWN) type_check(z,0);    /* yukk!!! */
      genop(CMP); gojmp(JMPFALSE,l1);
      compile(); gojmp(JMP,ldone);
      stufflabel(l1);
    }
  } while (gaze_ahead(TOKEN,STRING,NUMBER,BOOLEAN,0));
  stufflabel(ldone); genop(POP);
  return UNKNOWN;
}