UNIX — универсальная среда программирования - Керниган Брайан Уилсон
static Symbol *symlist =0; /* symbol table: linked list */
Symbol *lookup(s) /* find s in symbol table */
char *s;
{
Symbol *sp;
for (sp = symlist; sp != (Symbol*)0; sp = sp->next)
if (strcmp(sp->name, s) == 0)
return sp;
return 0; /* 0 ==> not found */
}
Symbol *install(s, t, d) /* install s in symbol table */
char *s;
int t;
double d;
{
Symbol *sp;
char *emalloc();
sp = (Symbol*)emalloc(sizeof(Symbol));
sp->name = emalloc(strlen(s)+1); /* +1 for ' ' */
strcpy(sp->name, s);
sp->type = t;
sp->u.val = d;
sp->next = symlist; /* put at front of list */
symlist = sp;
return sp;
}
char *emalloc(n) /* check return from malloc */
unsigned n;
{
char *p, *malloc();
p = malloc(n);
if (p == 0)
execerror("out of memory", (char*)0);
return p;
}
3.5 hoc4
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();
