3.5.1 code.c

3.5.1 code.c

#include "hoc.h"

#include "y.tab.h"

#define NSTACK 256

static Datum stack[NSTACK]; /* the stack */

static Datum *stackp; /* next free spot on stack */

#define NPROG 2000

Inst prog[NPROG]; /* the machine */

Inst *progp; /* next free spot for code generation */

Inst *pc; /* program counter during execution */

initcode() /* initialize for code generation */

{

 stackp = stack;

 progp = prog;

}

push(d) /* push d onto stack */

 Datum d;

{

 if (stackp >= &stack[NSTACK])

  execerror("stack overflow", (char*)0);

 *stackp++ = d;

}

Datum pop() /* pop and return top elem from stack */

{

 if (stackp <= stack)

  execerror("stack underflow", (char*)0);

 return *--stackp;

}

constpush() /* push constant onto stack */

{

 Datum d;

 d.val = ((Symbol*)*pc++)->u.val;

 push(d);

}

varpush() /* push variable onto stack */

{

 Datum d;

 d.sym = (Symbol*)(*pc++);

 push(d);

}

bltin() /* evaluate built-in on top of stack */

{

 Datum d;

 d = pop();

 d.val = (*(double(*)())(*pc++))(d.val);

 push(d);

}

eval() /* evaluate variable on stack */

{

 Datum d;

 d = pop() ;

 if (d.sym->type == UNDEF)

  execerror("undefined variable", d.sym->name);

 d.val = d.sym->u.val;

 push(d);

}

add() /* add top two elems on stack */

{

 Datum d1, d2;

 d2 = pop();

 d1 = pop();

 d1.val += d2.val;

 push(d1);

}

sub() /* subtract top of stack from next */

{

 Datum d1, d2;

 d2 = pop();

 d1 = pop();

 d1.val -= d2.val;

 push(d1);

}

mul() {

 Datum d1, d2;

 d2 = pop();

 d1 = pop();

 d1.val *= d2.val;

 push(d1);

}

div() {

 Datum d1, d2;

 d2 = pop();

 if (d2.val == 0.0)

  execerror("division by zero", (char*)0);

 d1 = pop();

 d1.val /= d2.val;

 push(d1);

}

negate() {

 Datum d;

 d = pop();

 d.val = -d.val;

 push(d);

}

power() {

 Datum d1, d2;

 extern double Pow();

 d2 = pop();

 d1 = pop();

 d1.val = Pow(d1.val, d2.val);

 push(d1);

}

assign() /* assign top value to next value */

{

 Datum d1, d2;

 d1= pop();

 d2 = pop();

 if (d1.sym->type != VAR && d1.sym->type != UNDEF)

  execerror("assignment to non-variable", d1.sym->name);

 d1.sym->u.val = d2.val;

 d1.sym->type = VAR;

 push(d2);

}

print() /* pop top value from stack, print it */

{

 Datum d;

 d = pop();

 printf(" %8g ", d.val);

}

Inst *code(f) /* install one instruction or operand */

 Inst f;

{

 Inst *oprogp = progp;

 if (progp >= &eprog[NPROG])

  execerror("program too big", (char*)0);

 *progp++ = f;

 return oprogp;

}

execute(p) /* run the machine */

 Inst *p;

{

 for (pc = p; *pc != STOP; )

  (*(*pc++))();

}