alloc.c

#define ALLOCSIZE 100

static char allocbuf[ALLOCSIZE];
static char *allocp = &allocbuf[0];

static void movemem(char *start);
char *smartalloc(int n, char *begin);

/**
 * n - lenght of asking memory
 * *begin - pointer to beginning interest blocks
 */
char *smartalloc(int n, char *begin)
{
    /* if first calling, begin set to buffer-begin */
    begin = (begin == 0) ? allocbuf : begin; // begin == 0 eq begin == NULL
    if (allocbuf + ALLOCSIZE - allocp >= n) {
        allocp += n;
        return allocp - n;
    }
    else {  /* buffer full */
        movemem(begin);
        if (allocbuf + ALLOCSIZE - allocp >= n) {
            allocp += n;
            return allocp - n;
        }
        else
            return 0; /* movemem does not solve problem */
    }
}

/**
 * move important memory blocks (it start from *start) to buffer-begin
 */
static void movemem(char *begin)
{
    if (begin > allocbuf && begin < allocp) {
        char *p = &allocbuf[0];
        while (begin < allocp)
            *p++ = *begin++;
        allocp = p;
    }
}