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_GETTING A HANDLE ON VIRTUAL MEMORY_
by Walter Bright
[LISTING ONE]
/* Compile with: ZTC wc -ml */
/* (Use large model so strcmp() can handle far pointers.) */
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <ctype.h>
#include <handle.h>
struct tree
{
char __handle *word;
int count;
struct tree __handle *left;
struct tree __handle *right;
};
int readword(char *w, int nbytes)
{
int c;
do {
c = getchar();
if (c == EOF)
return 0;
}
while (!isalpha(c));
do {
if (nbytes > 1)
{
*w++ = c;
nbytes--;
}
c = getchar();
}
while (isalnum(c));
*w = 0;
return 1;
}
void tree_insert(struct tree __handle * __handle *pt, char *w)
{
int cmp;
struct tree __handle *p;
while ((p = *pt) != NULL)
{
if ((cmp = strcmp(w,p->word)) == 0)
goto gotit;
pt = (cmp < 0) ? &p->left : &p->right;
}
p = (struct tree __handle *) handle_calloc(sizeof(struct tree));
if (!p || (p->word = handle_strdup(w)) == NULL)
{
printf("Out of memory\n");
exit(EXIT_FAILURE);
}
*pt = p;
gotit:
p->count++;
}
tree_print(struct tree __handle *p)
{
while (p)
{
tree_print(p->left);
printf("%5d %s\n",p->count,(char far *)p->word);
p = p->right;
}
}
tree_free(struct tree __handle *p)
{
struct tree __handle *pn;
while (p)
{
handle_free(p->word);
tree_free(p->left);
pn = p->right;
handle_free(p);
p = pn;
}
}
main()
{
struct tree __handle *root = NULL;
char word[32];
while (readword(word,sizeof(word)))
tree_insert(&root, word);
tree_print(root);
tree_free(root);
return EXIT_SUCCESS;
}
[Figure 1: Typical pointer types used in most PC implementations of C]
void *p; /* pointer type is default for the memory model */
char far *pc; /* far (segment and offset pair) pointer */
int near *p; /* near (offset only, segment is assumed) */
[Figure 2: Converting pointers from handle to far]
R 65,T 5
int __handle *h;
struct A __handle *h2;
int far *f;
int i;
extern void func(int far *pi);
f = h;
*h = i;
h[3] = *f;
i = *(h + 6);
h2->b = i;
func(h);
h = (int far *) h;
[Figure 3: Example showing that the optimizer is handle aware]
struct { int a,b; } __handle *h;
h->a = 1;
h->b = 2;
/* Converted code */
struct { int a,b; } __handle *h, far *p;
p = h;
p->a = 1;
p->b = 2;