path: root/realloc.c

#include "malloc.h"
#include <assert.h>
#include <string.h>

void*
__realloc_impl(heap_cache_t *cache, void *ptr, size_t w)
{
    if(w == 0) {
        DBGPRINT("realloc: called with w == 0, freeing %p\n", ptr);
        __free_impl(cache, ptr);
        return NULL;
    }
    if(ptr == NULL) {
        DBGPRINT("realloc: called with NULL ptr, alloc %i\n", w);
        return __malloc_impl(cache, w);
    }

    w = REALW(w);
    bucket_obj_t *obj = OBJ_FROM_PTR(ptr);

    assert(OBJ_VALID(obj));
    size_t objw = OBJ_WIDTH(obj);
    if(objw > w) return ptr;

    size_t wdiff = w - objw;
    DBGPRINT("realloc: ptr %p needs %i new bytes\n", ptr, wdiff);

    bucket_obj_t *after = OBJ_AFTER(obj);
    size_t afterw = 0;
    bucket_t *bucket = __bucket_from_obj(cache, obj);
    void *newptr = NULL;

    if(bucket == NULL)
        goto resize_fail;

    if((uintptr_t)after > bucket->limit) goto resize_fail;
    assert(OBJ_VALID(after));
    afterw = OBJ_WIDTH(after);

    if(OBJ_TAKEN(after))
        goto resize_fail;
    
    DBGPRINT("realloc: obj %p after obj %p is free (w %i)\n", after, obj, afterw);
    if(objw + sizeof(bucket_obj_t) + afterw < w)
        goto resize_fail;

    obj->size_taken = w | 1;
    if(bucket->firstfree == after)
        bucket->firstfree = OBJ_AFTER(obj);

    after = OBJ_AFTER(obj);
    *after = (bucket_obj_t){
        .checksum = OBJ_CHECKSUM,
        .size_taken = afterw - wdiff
    };
    DBGPRINT("realloc: moved obj %p (%i) to resize obj %p (%i)\n", 
            after, after->size_taken, obj, obj->size_taken);
    return ptr;

resize_fail:
    DBGPRINT("realloc: could not resize existing object, calling malloc\n");
    newptr = __malloc_impl(cache, w);
    memcpy(newptr, ptr, obj->size_taken & ~1);
    __free_impl(cache, ptr);
    return newptr;
}