/*      $OpenBSD: alloc.c,v 1.19 2018/01/16 22:52:32 jca Exp $  */

/* Public domain, like most of the rest of ksh */

/*
 * area-based allocation built on malloc/free
 */

#include <stdint.h>
#include <stdlib.h>

#include "sh.h"

struct link {
        struct link *prev;
        struct link *next;
};

Area *
ainit(Area *ap)
{
        ap->freelist = NULL;
        return ap;
}

void
afreeall(Area *ap)
{
        struct link *l, *l2;

        for (l = ap->freelist; l != NULL; l = l2) {
                l2 = l->next;
                free(l);
        }
        ap->freelist = NULL;
}

#define L2P(l)  ( (void *)(((char *)(l)) + sizeof(struct link)) )
#define P2L(p)  ( (struct link *)(((char *)(p)) - sizeof(struct link)) )

void *
alloc(size_t size, Area *ap)
{
        struct link *l;

        /* ensure that we don't overflow by allocating space for link */
        if (size > SIZE_MAX - sizeof(struct link))
                internal_errorf("unable to allocate memory");

        l = malloc(sizeof(struct link) + size);
        if (l == NULL)
                internal_errorf("unable to allocate memory");
        l->next = ap->freelist;
        l->prev = NULL;
        if (ap->freelist)
                ap->freelist->prev = l;
        ap->freelist = l;

        return L2P(l);
}

/*
 * Copied from calloc().
 *
 * This is sqrt(SIZE_MAX+1), as s1*s2 <= SIZE_MAX
 * if both s1 < MUL_NO_OVERFLOW and s2 < MUL_NO_OVERFLOW
 */
#define MUL_NO_OVERFLOW (1UL << (sizeof(size_t) * 4))

void *
areallocarray(void *ptr, size_t nmemb, size_t size, Area *ap)
{
        /* condition logic cloned from calloc() */
        if ((nmemb >= MUL_NO_OVERFLOW || size >= MUL_NO_OVERFLOW) &&
            nmemb > 0 && SIZE_MAX / nmemb < size) {
                internal_errorf("unable to allocate memory");
        }

        return aresize(ptr, nmemb * size, ap);
}

void *
aresize(void *ptr, size_t size, Area *ap)
{
        struct link *l, *l2, *lprev, *lnext;

        if (ptr == NULL)
                return alloc(size, ap);

        /* ensure that we don't overflow by allocating space for link */
        if (size > SIZE_MAX - sizeof(struct link))
                internal_errorf("unable to allocate memory");

        l = P2L(ptr);
        lprev = l->prev;
        lnext = l->next;

        l2 = realloc(l, sizeof(struct link) + size);
        if (l2 == NULL)
                internal_errorf("unable to allocate memory");
        if (lprev)
                lprev->next = l2;
        else
                ap->freelist = l2;
        if (lnext)
                lnext->prev = l2;

        return L2P(l2);
}

void
afree(void *ptr, Area *ap)
{
        struct link *l;

        if (!ptr)
                return;

        l = P2L(ptr);
        if (l->prev)
                l->prev->next = l->next;
        else
                ap->freelist = l->next;
        if (l->next)
                l->next->prev = l->prev;

        free(l);
}