src/iterator.c

/*
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS HEADER.
 *
 * Copyright 2024 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/iterator.h"

#include <string.h>

static bool cx_iter_valid(void const *it) {
    struct cx_iterator_s const *iter = it;
    return iter->index < iter->elem_count;
}

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

static void cx_iter_next_fast(void *it) {
    struct cx_iterator_base_s *itbase = it;
    if (itbase->remove) {
        struct cx_mut_iterator_s *iter = it;
        itbase->remove = false;
        iter->elem_count--;
        // only move the last element when we are not currently aiming
        // at the last element already
        if (iter->index < iter->elem_count) {
            void *last = ((char *) iter->src_handle)
                         + iter->elem_count * iter->elem_size;
            memcpy(iter->elem_handle, last, iter->elem_size);
        }
    } else {
        struct cx_iterator_s *iter = it;
        iter->index++;
        iter->elem_handle = ((char *) iter->elem_handle) + iter->elem_size;
    }
}

static void cx_iter_next_slow(void *it) {
    struct cx_iterator_base_s *itbase = it;
    if (itbase->remove) {
        struct cx_mut_iterator_s *iter = it;
        itbase->remove = false;
        iter->elem_count--;

        // number of elements to move
        size_t remaining = iter->elem_count - iter->index;
        if (remaining > 0) {
            memmove(
                    iter->elem_handle,
                    ((char *) iter->elem_handle) + iter->elem_size,
                    remaining * iter->elem_size
            );
        }
    } else {
        struct cx_iterator_s *iter = it;
        iter->index++;
        iter->elem_handle = ((char *) iter->elem_handle) + iter->elem_size;
    }
}

CxMutIterator cxMutIterator(
        void *array,
        size_t elem_size,
        size_t elem_count,
        bool remove_keeps_order
) {
    CxMutIterator iter;

    iter.index = 0;
    iter.src_handle = array;
    iter.elem_handle = array;
    iter.elem_size = elem_size;
    iter.elem_count = array == NULL ? 0 : elem_count;
    iter.base.valid = cx_iter_valid;
    iter.base.current = cx_iter_current;
    iter.base.next = remove_keeps_order ? cx_iter_next_slow : cx_iter_next_fast;
    iter.base.remove = false;
    iter.base.mutating = true;

    return iter;
}

CxIterator cxIterator(
        void const *array,
        size_t elem_size,
        size_t elem_count
) {
    CxMutIterator iter = cxMutIterator((void*)array, elem_size, elem_count, false);
    iter.base.mutating = false;

    // we know the iterators share the same memory layout
    CxIterator ret;
    memcpy(&ret, &iter, sizeof(CxIterator));
    return ret;
}