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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;