src/array_list.c

/*
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS HEADER.
 *
 * Copyright 2021 Mike Becker, Olaf Wintermann All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are met:
 *
 *   1. Redistributions of source code must retain the above copyright
 *      notice, this list of conditions and the following disclaimer.
 *
 *   2. Redistributions in binary form must reproduce the above copyright
 *      notice, this list of conditions and the following disclaimer in the
 *      documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
 * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE
 * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
 * POSSIBILITY OF SUCH DAMAGE.
 */

#include "cx/array_list.h"
#include "cx/compare.h"
#include <assert.h>
#include <string.h>
#include <errno.h>

// Default array reallocator

static void *cx_array_default_realloc(
        void *array,
        size_t capacity,
        size_t elem_size,
        cx_attr_unused CxArrayReallocator *alloc
) {
    return realloc(array, capacity * elem_size);
}

CxArrayReallocator cx_array_default_reallocator_impl = {
        cx_array_default_realloc, NULL, NULL, 0, 0
};

CxArrayReallocator *cx_array_default_reallocator = &cx_array_default_reallocator_impl;

// Stack-aware array reallocator

static void *cx_array_advanced_realloc(
        void *array,
        size_t capacity,
        size_t elem_size,
        cx_attr_unused CxArrayReallocator *alloc
) {
    // retrieve the pointer to the actual allocator
    const CxAllocator *al = alloc->ptr1;

    // check if the array is still located on the stack
    void *newmem;
    if (array == alloc->ptr2) {
        newmem = cxMalloc(al, capacity * elem_size);
        if (newmem != NULL && array != NULL) {
            memcpy(newmem, array, capacity * elem_size);
        }
    } else {
        newmem = cxRealloc(al, array, capacity * elem_size);
    }
    return newmem;
}

struct cx_array_reallocator_s cx_array_reallocator(
        const struct cx_allocator_s *allocator,
        const void *stackmem
) {
    if (allocator == NULL) {
        allocator = cxDefaultAllocator;
    }
    return (struct cx_array_reallocator_s) {
            cx_array_advanced_realloc,
            (void*) allocator, (void*) stackmem,
            0, 0
    };
}

// LOW LEVEL ARRAY LIST FUNCTIONS

int cx_array_reserve(
        void **array,
        void *size,
        void *capacity,
        unsigned width,
        size_t elem_size,
        size_t elem_count,
        CxArrayReallocator *reallocator
) {
    // assert pointers
    assert(array != NULL);
    assert(size != NULL);
    assert(capacity != NULL);
    assert(reallocator != NULL);

    // determine size and capacity
    size_t oldcap;
    size_t oldsize;
    size_t max_size;
    if (width == 0 || width == CX_WORDSIZE) {
        oldcap = *(size_t*) capacity;
        oldsize = *(size_t*) size;
        max_size = SIZE_MAX;
    } else if (width == 16) {
        oldcap = *(uint16_t*) capacity;
        oldsize = *(uint16_t*) size;
        max_size = UINT16_MAX;
    } else if (width == 8) {
        oldcap = *(uint8_t*) capacity;
        oldsize = *(uint8_t*) size;
        max_size = UINT8_MAX;
    }
#if CX_WORDSIZE == 64
    else if (width == 32) {
        oldcap = *(uint32_t*) capacity;
        oldsize = *(uint32_t*) size;
        max_size = UINT32_MAX;
    }
#endif
    else {
        errno = EINVAL;
        return 1;
    }

    // assert that the array is allocated when it has capacity
    assert(*array != NULL || oldcap == 0);

    // determine new capacity
    size_t newcap = oldsize + elem_count;

    // check for overflow
    if (newcap > max_size) {
        errno = EOVERFLOW;
        return 1;
    }

    // reallocate if possible
    if (newcap > oldcap) {
        // calculate new capacity (next number divisible by 16)
        newcap = newcap - (newcap % 16) + 16;

        // perform reallocation
        void *newmem = reallocator->realloc(
                *array, newcap, elem_size, reallocator
        );
        if (newmem == NULL) {
            return 1;
        }

        // store new pointer
        *array = newmem;

        // store new capacity
        if (width == 0 || width == CX_WORDSIZE) {
            *(size_t*) capacity = newcap;
        } else if (width == 16) {
            *(uint16_t*) capacity = (uint16_t) newcap;
        } else if (width == 8) {
            *(uint8_t*) capacity = (uint8_t) newcap;
        }
#if CX_WORDSIZE == 64
        else if (width == 32) {
            *(uint32_t*) capacity = (uint32_t) newcap;
        }
#endif
    }

    return 0;
}

int cx_array_copy(
        void **target,
        void *size,
        void *capacity,
        unsigned width,
        size_t index,
        const void *src,
        size_t elem_size,
        size_t elem_count,
        CxArrayReallocator *reallocator
) {
    // assert pointers
    assert(target != NULL);
    assert(size != NULL);
    assert(capacity != NULL);
    assert(src != NULL);
    assert(reallocator != NULL);

    // determine size and capacity
    size_t oldcap;
    size_t oldsize;
    size_t max_size;
    if (width == 0 || width == CX_WORDSIZE) {
        oldcap = *(size_t*) capacity;
        oldsize = *(size_t*) size;
        max_size = SIZE_MAX;
    } else if (width == 16) {
        oldcap = *(uint16_t*) capacity;
        oldsize = *(uint16_t*) size;
        max_size = UINT16_MAX;
    } else if (width == 8) {
        oldcap = *(uint8_t*) capacity;
        oldsize = *(uint8_t*) size;
        max_size = UINT8_MAX;
    }
#if CX_WORDSIZE == 64
    else if (width == 32) {
        oldcap = *(uint32_t*) capacity;
        oldsize = *(uint32_t*) size;
        max_size = UINT32_MAX;
    }
#endif
    else {
        errno = EINVAL;
        return 1;
    }

    // assert that the array is allocated when it has capacity
    assert(*target != NULL || oldcap == 0);

    // check if resize is required
    size_t minsize = index + elem_count;
    size_t newsize = oldsize < minsize ? minsize : oldsize;

    // check for overflow
    if (newsize > max_size) {
        errno = EOVERFLOW;
        return 1;
    }

    // reallocate if possible
    size_t newcap = oldcap;
    if (newsize > oldcap) {
        // check, if we need to repair the src pointer
        uintptr_t targetaddr = (uintptr_t) *target;
        uintptr_t srcaddr = (uintptr_t) src;
        bool repairsrc = targetaddr <= srcaddr
                         && srcaddr < targetaddr + oldcap * elem_size;

        // calculate new capacity (next number divisible by 16)
        newcap = newsize - (newsize % 16) + 16;
        assert(newcap > newsize);

        // perform reallocation
        void *newmem = reallocator->realloc(
                *target, newcap, elem_size, reallocator
        );
        if (newmem == NULL) {
            return 1;
        }

        // repair src pointer, if necessary
        if (repairsrc) {
            src = ((char *) newmem) + (srcaddr - targetaddr);
        }

        // store new pointer
        *target = newmem;
    }

    // determine target pointer
    char *start = *target;
    start += index * elem_size;

    // copy elements and set new size
    memmove(start, src, elem_count * elem_size);

    // if any of size or capacity changed, store them back
    if (newsize != oldsize || newcap != oldcap) {
        if (width == 0 || width == CX_WORDSIZE) {
            *(size_t*) capacity = newcap;
            *(size_t*) size = newsize;
        } else if (width == 16) {
            *(uint16_t*) capacity = (uint16_t) newcap;
            *(uint16_t*) size = (uint16_t) newsize;
        } else if (width == 8) {
            *(uint8_t*) capacity = (uint8_t) newcap;
            *(uint8_t*) size = (uint8_t) newsize;
        }
#if CX_WORDSIZE == 64
        else if (width == 32) {
            *(uint32_t*) capacity = (uint32_t) newcap;
            *(uint32_t*) size = (uint32_t) newsize;
        }
#endif
    }

    // return successfully
    return 0;
}

int cx_array_insert_sorted(
        void **target,
        size_t *size,
        size_t *capacity,
        cx_compare_func cmp_func,
        const void *sorted_data,
        size_t elem_size,
        size_t elem_count,
        CxArrayReallocator *reallocator
) {
    // assert pointers
    assert(target != NULL);
    assert(size != NULL);
    assert(capacity != NULL);
    assert(cmp_func != NULL);
    assert(sorted_data != NULL);
    assert(reallocator != NULL);

    // corner case
    if (elem_count == 0) return 0;

    // store some counts
    size_t old_size = *size;
    size_t needed_capacity = old_size + elem_count;

    // if we need more than we have, try a reallocation
    if (needed_capacity > *capacity) {
        size_t new_capacity = needed_capacity - (needed_capacity % 16) + 16;
        void *new_mem = reallocator->realloc(
                *target, new_capacity, elem_size, reallocator
        );
        if (new_mem == NULL) {
            // give it up right away, there is no contract
            // that requires us to insert as much as we can
            return 1;
        }
        *target = new_mem;
        *capacity = new_capacity;
    }

    // now we have guaranteed that we can insert everything
    size_t new_size = old_size + elem_count;
    *size = new_size;

    // declare the source and destination indices/pointers
    size_t si = 0, di = 0;
    const char *src = sorted_data;
    char *dest = *target;

    // find the first insertion point
    di = cx_array_binary_search_sup(dest, old_size, elem_size, src, cmp_func);
    dest += di * elem_size;

    // move the remaining elements in the array completely to the right
    // we will call it the "buffer" for parked elements
    size_t buf_size = old_size - di;
    size_t bi = new_size - buf_size;
    char *bptr = ((char *) *target) + bi * elem_size;
    memmove(bptr, dest, buf_size * elem_size);

    // while there are both source and buffered elements left,
    // copy them interleaving
    while (si < elem_count && bi < new_size) {
        // determine how many source elements can be inserted
        size_t copy_len, bytes_copied;
        copy_len = cx_array_binary_search_sup(
                src,
                elem_count - si,
                elem_size,
                bptr,
                cmp_func
        );

        // copy the source elements
        bytes_copied = copy_len * elem_size;
        memcpy(dest, src, bytes_copied);
        dest += bytes_copied;
        src += bytes_copied;
        si += copy_len;

        // when all source elements are in place, we are done
        if (si >= elem_count) break;

        // determine how many buffered elements need to be restored
        copy_len = cx_array_binary_search_sup(
                bptr,
                new_size - bi,
                elem_size,
                src,
                cmp_func
        );

        // restore the buffered elements
        bytes_copied = copy_len * elem_size;
        memmove(dest, bptr, bytes_copied);
        dest += bytes_copied;
        bptr += bytes_copied;
        bi += copy_len;
    }

    // still source elements left? simply append them
    if (si < elem_count) {
        memcpy(dest, src, elem_size * (elem_count - si));
    }

    // still buffer elements left?
    // don't worry, we already moved them to the correct place

    return 0;
}

size_t cx_array_binary_search_inf(
        const void *arr,
        size_t size,
        size_t elem_size,
        const void *elem,
        cx_compare_func cmp_func
) {
    // special case: empty array
    if (size == 0) return 0;

    // declare a variable that will contain the compare results
    int result;

    // cast the array pointer to something we can use offsets with
    const char *array = arr;

    // check the first array element
    result = cmp_func(elem, array);
    if (result < 0) {
        return size;
    } else if (result == 0) {
        return 0;
    }

    // check the last array element
    result = cmp_func(elem, array + elem_size * (size - 1));
    if (result >= 0) {
        return size - 1;
    }

    // the element is now guaranteed to be somewhere in the list
    // so start the binary search
    size_t left_index = 1;
    size_t right_index = size - 1;
    size_t pivot_index;

    while (left_index <= right_index) {
        pivot_index = left_index + (right_index - left_index) / 2;
        const char *arr_elem = array + pivot_index * elem_size;
        result = cmp_func(elem, arr_elem);
        if (result == 0) {
            // found it!
            return pivot_index;
        } else if (result < 0) {
            // element is smaller than pivot, continue search left
            right_index = pivot_index - 1;
        } else {
            // element is larger than pivot, continue search right
            left_index = pivot_index + 1;
        }
    }

    // report the largest upper bound
    return result < 0 ? (pivot_index - 1) : pivot_index;
}

size_t cx_array_binary_search(
        const void *arr,
        size_t size,
        size_t elem_size,
        const void *elem,
        cx_compare_func cmp_func
) {
    size_t index = cx_array_binary_search_inf(
            arr, size, elem_size, elem, cmp_func
    );
    if (index < size &&
            cmp_func(((const char *) arr) + index * elem_size, elem) == 0) {
        return index;
    } else {
        return size;
    }
}

size_t cx_array_binary_search_sup(
        const void *arr,
        size_t size,
        size_t elem_size,
        const void *elem,
        cx_compare_func cmp_func
) {
    size_t inf = cx_array_binary_search_inf(
            arr, size, elem_size, elem, cmp_func
    );
    if (inf == size) {
        // no infimum means, first element is supremum
        return 0;
    } else if (cmp_func(((const char *) arr) + inf * elem_size, elem) == 0) {
        return inf;
    } else {
        return inf + 1;
    }
}

#ifndef CX_ARRAY_SWAP_SBO_SIZE
#define CX_ARRAY_SWAP_SBO_SIZE 128
#endif
const unsigned cx_array_swap_sbo_size = CX_ARRAY_SWAP_SBO_SIZE;

void cx_array_swap(
        void *arr,
        size_t elem_size,
        size_t idx1,
        size_t idx2
) {
    assert(arr != NULL);

    // short circuit
    if (idx1 == idx2) return;

    char sbo_mem[CX_ARRAY_SWAP_SBO_SIZE];
    void *tmp;

    // decide if we can use the local buffer
    if (elem_size > CX_ARRAY_SWAP_SBO_SIZE) {
        tmp = malloc(elem_size);
        // we don't want to enforce error handling
        if (tmp == NULL) abort();
    } else {
        tmp = sbo_mem;
    }

    // calculate memory locations
    char *left = arr, *right = arr;
    left += idx1 * elem_size;
    right += idx2 * elem_size;

    // three-way swap
    memcpy(tmp, left, elem_size);
    memcpy(left, right, elem_size);
    memcpy(right, tmp, elem_size);

    // free dynamic memory, if it was needed
    if (tmp != sbo_mem) {
        free(tmp);
    }
}

// HIGH LEVEL ARRAY LIST FUNCTIONS

typedef struct {
    struct cx_list_s base;
    void *data;
    size_t capacity;
    CxArrayReallocator reallocator;
} cx_array_list;

static void cx_arl_destructor(struct cx_list_s *list) {
    cx_array_list *arl = (cx_array_list *) list;

    char *ptr = arl->data;

    if (list->collection.simple_destructor) {
        for (size_t i = 0; i < list->collection.size; i++) {
            cx_invoke_simple_destructor(list, ptr);
            ptr += list->collection.elem_size;
        }
    }
    if (list->collection.advanced_destructor) {
        for (size_t i = 0; i < list->collection.size; i++) {
            cx_invoke_advanced_destructor(list, ptr);
            ptr += list->collection.elem_size;
        }
    }

    cxFree(list->collection.allocator, arl->data);
    cxFree(list->collection.allocator, list);
}

static size_t cx_arl_insert_array(
        struct cx_list_s *list,
        size_t index,
        const void *array,
        size_t n
) {
    // out of bounds and special case check
    if (index > list->collection.size || n == 0) return 0;

    // get a correctly typed pointer to the list
    cx_array_list *arl = (cx_array_list *) list;

    // do we need to move some elements?
    if (index < list->collection.size) {
        const char *first_to_move = (const char *) arl->data;
        first_to_move += index * list->collection.elem_size;
        size_t elems_to_move = list->collection.size - index;
        size_t start_of_moved = index + n;

        if (cx_array_copy(
                &arl->data,
                &list->collection.size,
                &arl->capacity,
                0,
                start_of_moved,
                first_to_move,
                list->collection.elem_size,
                elems_to_move,
                &arl->reallocator
        )) {
            // if moving existing elems is unsuccessful, abort
            return 0;
        }
    }

    // note that if we had to move the elements, the following operation
    // is guaranteed to succeed, because we have the memory already allocated
    // therefore, it is impossible to leave this function with an invalid array

    // place the new elements
    if (cx_array_copy(
            &arl->data,
            &list->collection.size,
            &arl->capacity,
            0,
            index,
            array,
            list->collection.elem_size,
            n,
            &arl->reallocator
    )) {
        // array list implementation is "all or nothing"
        return 0;
    } else {
        return n;
    }
}

static size_t cx_arl_insert_sorted(
        struct cx_list_s *list,
        const void *sorted_data,
        size_t n
) {
    // get a correctly typed pointer to the list
    cx_array_list *arl = (cx_array_list *) list;

    if (cx_array_insert_sorted(
            &arl->data,
            &list->collection.size,
            &arl->capacity,
            list->collection.cmpfunc,
            sorted_data,
            list->collection.elem_size,
            n,
            &arl->reallocator
    )) {
        // array list implementation is "all or nothing"
        return 0;
    } else {
        return n;
    }
}

static int cx_arl_insert_element(
        struct cx_list_s *list,
        size_t index,
        const void *element
) {
    return 1 != cx_arl_insert_array(list, index, element, 1);
}

static int cx_arl_insert_iter(
        struct cx_iterator_s *iter,
        const void *elem,
        int prepend
) {
    struct cx_list_s *list = iter->src_handle.m;
    if (iter->index < list->collection.size) {
        int result = cx_arl_insert_element(
                list,
                iter->index + 1 - prepend,
                elem
        );
        if (result == 0) {
            iter->elem_count++;
            if (prepend != 0) {
                iter->index++;
                iter->elem_handle = ((char *) iter->elem_handle) + list->collection.elem_size;
            }
        }
        return result;
    } else {
        int result = cx_arl_insert_element(list, list->collection.size, elem);
        if (result == 0) {
            iter->elem_count++;
            iter->index = list->collection.size;
        }
        return result;
    }
}

static size_t cx_arl_remove(
        struct cx_list_s *list,
        size_t index,
        size_t num,
        void *targetbuf
) {
    cx_array_list *arl = (cx_array_list *) list;

    // out-of-bounds check
    size_t remove;
    if (index >= list->collection.size) {
        remove = 0;
    } else if (index + num > list->collection.size) {
        remove = list->collection.size - index;
    } else {
        remove = num;
    }

    // easy exit
    if (remove == 0) return 0;

    // destroy or copy contents
    if (targetbuf == NULL) {
        for (size_t idx = index; idx < index + remove; idx++) {
            cx_invoke_destructor(
                    list,
                    ((char *) arl->data) + idx * list->collection.elem_size
            );
        }
    } else {
        memcpy(
                targetbuf,
                ((char *) arl->data) + index * list->collection.elem_size,
                remove * list->collection.elem_size
        );
    }

    // short-circuit removal of last elements
    if (index + remove == list->collection.size) {
        list->collection.size -= remove;
        return remove;
    }

    // just move the elements to the left
    int result = cx_array_copy(
            &arl->data,
            &list->collection.size,
            &arl->capacity,
            0,
            index,
            ((char *) arl->data) + (index + remove) * list->collection.elem_size,
            list->collection.elem_size,
            list->collection.size - index - remove,
            &arl->reallocator
    );

    // cx_array_copy cannot fail, array cannot grow
    assert(result == 0);

    // decrease the size
    list->collection.size -= remove;

    return remove;
}

static void cx_arl_clear(struct cx_list_s *list) {
    if (list->collection.size == 0) return;

    cx_array_list *arl = (cx_array_list *) list;
    char *ptr = arl->data;

    if (list->collection.simple_destructor) {
        for (size_t i = 0; i < list->collection.size; i++) {
            cx_invoke_simple_destructor(list, ptr);
            ptr += list->collection.elem_size;
        }
    }
    if (list->collection.advanced_destructor) {
        for (size_t i = 0; i < list->collection.size; i++) {
            cx_invoke_advanced_destructor(list, ptr);
            ptr += list->collection.elem_size;
        }
    }

    memset(arl->data, 0, list->collection.size * list->collection.elem_size);
    list->collection.size = 0;
}

static int cx_arl_swap(
        struct cx_list_s *list,
        size_t i,
        size_t j
) {
    if (i >= list->collection.size || j >= list->collection.size) return 1;
    cx_array_list *arl = (cx_array_list *) list;
    cx_array_swap(arl->data, list->collection.elem_size, i, j);
    return 0;
}

static void *cx_arl_at(
        const struct cx_list_s *list,
        size_t index
) {
    if (index < list->collection.size) {
        const cx_array_list *arl = (const cx_array_list *) list;
        char *space = arl->data;
        return space + index * list->collection.elem_size;
    } else {
        return NULL;
    }
}

static ssize_t cx_arl_find_remove(
        struct cx_list_s *list,
        const void *elem,
        bool remove
) {
    assert(list->collection.cmpfunc != NULL);
    assert(list->collection.size < SIZE_MAX / 2);
    char *cur = ((const cx_array_list *) list)->data;

    for (ssize_t i = 0; i < (ssize_t) list->collection.size; i++) {
        if (0 == list->collection.cmpfunc(elem, cur)) {
            if (remove) {
                if (1 == cx_arl_remove(list, i, 1, NULL)) {
                    return i;
                } else {
                    return -1;
                }
            } else {
                return i;
            }
        }
        cur += list->collection.elem_size;
    }

    return -1;
}

static void cx_arl_sort(struct cx_list_s *list) {
    assert(list->collection.cmpfunc != NULL);
    qsort(((cx_array_list *) list)->data,
          list->collection.size,
          list->collection.elem_size,
          list->collection.cmpfunc
    );
}

static int cx_arl_compare(
        const struct cx_list_s *list,
        const struct cx_list_s *other
) {
    assert(list->collection.cmpfunc != NULL);
    if (list->collection.size == other->collection.size) {
        const char *left = ((const cx_array_list *) list)->data;
        const char *right = ((const cx_array_list *) other)->data;
        for (size_t i = 0; i < list->collection.size; i++) {
            int d = list->collection.cmpfunc(left, right);
            if (d != 0) {
                return d;
            }
            left += list->collection.elem_size;
            right += other->collection.elem_size;
        }
        return 0;
    } else {
        return list->collection.size < other->collection.size ? -1 : 1;
    }
}

static void cx_arl_reverse(struct cx_list_s *list) {
    if (list->collection.size < 2) return;
    void *data = ((const cx_array_list *) list)->data;
    size_t half = list->collection.size / 2;
    for (size_t i = 0; i < half; i++) {
        cx_array_swap(data, list->collection.elem_size, i, list->collection.size - 1 - i);
    }
}

static bool cx_arl_iter_valid(const void *it) {
    const struct cx_iterator_s *iter = it;
    const struct cx_list_s *list = iter->src_handle.c;
    return iter->index < list->collection.size;
}

static void *cx_arl_iter_current(const void *it) {
    const struct cx_iterator_s *iter = it;
    return iter->elem_handle;
}

static void cx_arl_iter_next(void *it) {
    struct cx_iterator_s *iter = it;
    if (iter->base.remove) {
        iter->base.remove = false;
        cx_arl_remove(iter->src_handle.m, iter->index, 1, NULL);
    } else {
        iter->index++;
        iter->elem_handle =
                ((char *) iter->elem_handle)
                + ((const struct cx_list_s *) iter->src_handle.c)->collection.elem_size;
    }
}

static void cx_arl_iter_prev(void *it) {
    struct cx_iterator_s *iter = it;
    const cx_array_list *list = iter->src_handle.c;
    if (iter->base.remove) {
        iter->base.remove = false;
        cx_arl_remove(iter->src_handle.m, iter->index, 1, NULL);
    }
    iter->index--;
    if (iter->index < list->base.collection.size) {
        iter->elem_handle = ((char *) list->data)
                            + iter->index * list->base.collection.elem_size;
    }
}


static struct cx_iterator_s cx_arl_iterator(
        const struct cx_list_s *list,
        size_t index,
        bool backwards
) {
    struct cx_iterator_s iter;

    iter.index = index;
    iter.src_handle.c = list;
    iter.elem_handle = cx_arl_at(list, index);
    iter.elem_size = list->collection.elem_size;
    iter.elem_count = list->collection.size;
    iter.base.valid = cx_arl_iter_valid;
    iter.base.current = cx_arl_iter_current;
    iter.base.next = backwards ? cx_arl_iter_prev : cx_arl_iter_next;
    iter.base.remove = false;
    iter.base.mutating = false;

    return iter;
}

static cx_list_class cx_array_list_class = {
        cx_arl_destructor,
        cx_arl_insert_element,
        cx_arl_insert_array,
        cx_arl_insert_sorted,
        cx_arl_insert_iter,
        cx_arl_remove,
        cx_arl_clear,
        cx_arl_swap,
        cx_arl_at,
        cx_arl_find_remove,
        cx_arl_sort,
        cx_arl_compare,
        cx_arl_reverse,
        cx_arl_iterator,
};

CxList *cxArrayListCreate(
        const CxAllocator *allocator,
        cx_compare_func comparator,
        size_t elem_size,
        size_t initial_capacity
) {
    if (allocator == NULL) {
        allocator = cxDefaultAllocator;
    }

    cx_array_list *list = cxCalloc(allocator, 1, sizeof(cx_array_list));
    if (list == NULL) return NULL;

    list->base.cl = &cx_array_list_class;
    list->base.collection.allocator = allocator;
    list->capacity = initial_capacity;

    if (elem_size > 0) {
        list->base.collection.elem_size = elem_size;
        list->base.collection.cmpfunc = comparator;
    } else {
        elem_size = sizeof(void *);
        list->base.collection.cmpfunc = comparator == NULL ? cx_cmp_ptr : comparator;
        cxListStorePointers((CxList *) list);
    }

    // allocate the array after the real elem_size is known
    list->data = cxCalloc(allocator, initial_capacity, elem_size);
    if (list->data == NULL) {
        cxFree(allocator, list);
        return NULL;
    }

    // configure the reallocator
    list->reallocator = cx_array_reallocator(allocator, NULL);

    return (CxList *) list;
}