malloc()函数源代码

#include "types.h"
#include "stddef.h"
#include "string.h"

/* Imported functions */
extern void prom_printf (char *fmt, ...);

static char *malloc_ptr = 0;
static char *malloc_top = 0;
static char *last_alloc = 0;

void malloc_init(void *bottom, unsigned long size)
{
        malloc_ptr = bottom;
        malloc_top = bottom + size;
}

void malloc_dispose(void)
{
        malloc_ptr = 0;
        last_alloc = 0;
}

void *malloc (unsigned int size)
{
    char *caddr;

    if (!malloc_ptr)
        return NULL;
    if ((malloc_ptr + size + sizeof(int)) > malloc_top) {
        prom_printf("malloc failed\n");
        return NULL;
    }
    *(int *)malloc_ptr = size;
    caddr = malloc_ptr + sizeof(int);
    malloc_ptr += size + sizeof(int);
    last_alloc = caddr;
    malloc_ptr = (char *) ((((unsigned int) malloc_ptr) + 3) & (~3));
    return caddr;
}

void *realloc(void *ptr, unsigned int size)
{
    char *caddr, *oaddr = ptr;

    if (!malloc_ptr)
        return NULL;
    if (oaddr == last_alloc) {
        if (oaddr + size > malloc_top) {
                prom_printf("realloc failed\n");
                return NULL;
        }
        *(int *)(oaddr - sizeof(int)) = size;
        malloc_ptr = oaddr + size;
        return oaddr;
    }
    caddr = malloc(size);
    if (caddr != 0 && oaddr != 0)
        memcpy(caddr, oaddr, *(int *)(oaddr - sizeof(int)));
    return caddr;
}

void free (void *m)
{
    if (!malloc_ptr)
        return;
    if (m == last_alloc)
        malloc_ptr = (char *) last_alloc - sizeof(int);
}

void mark (void **ptr)
{
    if (!malloc_ptr)
        return;
    *ptr = (void *) malloc_ptr;
}

void release (void *ptr)
{
    if (!malloc_ptr)
        return;
    malloc_ptr = (char *) ptr;
}

char *strdup(char const *str)
{
    char *p = malloc(strlen(str) + 1);
    if (p)
         strcpy(p, str);
    return p;
}