apfl/src/resizable.c

#include <assert.h>
#include <stdlib.h>
#include <stddef.h>
#include <stdbool.h>
#include <string.h>

#include "alloc.h"
#include "resizable.h"

void
apfl_resizable_init(void **mem, size_t *len, size_t *cap)
{
    *mem = NULL;
    *len = 0;
    *cap = 0;
}

bool
apfl_resizable_resize(
    struct apfl_allocator allocator,
    size_t elem_size,
    void **mem,
    size_t *len,
    size_t *cap,
    size_t newlen
) {
    // TODO: We're wasteful here by never actually shrinking the memory.
    if (newlen <= *len || newlen < *cap) {
        *len = newlen;
        return true;
    }

    assert(newlen >= *cap);

    if (!apfl_resizable_ensure_cap(allocator, elem_size, mem, cap, newlen)) {
        return false;
    }

    *len = newlen;
    return true;
}

bool
apfl_resizable_ensure_cap(
    struct apfl_allocator allocator,
    size_t elem_size,
    void **mem,
    size_t *cap,
    size_t want_cap
) {
    if (want_cap <= *cap) {
        return true;
    }

    // TODO: We currently simply grow the memory to have space for exactly
    //       want_cap elements. It would probably be smarter to grow the memory
    //       a bit larger to reduce calls to realloc.
    void *newmem = REALLOC_BYTES(allocator, *mem, *cap * elem_size, want_cap * elem_size);
    if (newmem == NULL) {
        return false;
    }

    *mem = newmem;
    *cap = want_cap;
    return true;
}

bool
apfl_resizable_ensure_cap_for_more_elements(
    struct apfl_allocator allocator,
    size_t elem_size,
    void **mem,
    size_t len,
    size_t *cap,
    size_t more_elements
) {
    return apfl_resizable_ensure_cap(allocator, elem_size, mem, cap, len + more_elements); // TODO: What if len + more_elements overflows?
}

bool
apfl_resizable_check_cut_args(size_t len, size_t cut_start, size_t cut_len)
{
    return !(cut_start > len || cut_start + cut_len > len);
}

static void
move_elems_for_cut(
    size_t elem_size,
    void **mem,
    size_t len,
    size_t cut_start,
    size_t cut_len,
    size_t other_len
) {
    size_t src_off = cut_start + cut_len;
    size_t dst_off = cut_start + other_len;

    memmove(
        ((char *)(*mem)) + (dst_off * elem_size),
        ((char *)(*mem)) + (src_off * elem_size),
        (len - cut_start - cut_len) * elem_size
    );
}

bool
apfl_resizable_cut_without_resize(
    size_t elem_size,
    void **mem,
    size_t *len,
    size_t cut_start,
    size_t cut_len
) {
    if (!apfl_resizable_check_cut_args(*len, cut_start, cut_len)) {
        return false;
    }

    move_elems_for_cut(elem_size, mem, *len, cut_start, cut_len, 0);
    *len -= cut_len;

    return true;
}

bool
apfl_resizable_splice(
    struct apfl_allocator allocator,
    size_t elem_size,
    void **mem,
    size_t *len,
    size_t *cap,
    size_t cut_start,
    size_t cut_len,
    const void *other_mem,
    size_t other_len
) {
    if (!apfl_resizable_check_cut_args(*len, cut_start, cut_len)) {
        return false;
    }

    if (other_len > cut_len) {
        if (!apfl_resizable_ensure_cap_for_more_elements(
            allocator,
            elem_size,
            mem,
            *len,
            cap,
            other_len - cut_len
        )) {
            return false;
        }
    }

    move_elems_for_cut(elem_size, mem, *len, cut_start, cut_len, other_len);

    if (other_len > 0 && other_mem != NULL) {
        memcpy(
            ((char *)(*mem)) + cut_start * elem_size,
            other_mem,
            other_len * elem_size
        );
    }

    *len += other_len - cut_len;

    return true;
}

bool
apfl_resizable_append(struct apfl_allocator allocator, size_t elem_size, void **mem, size_t *len, size_t *cap, const void *other_mem, size_t other_len)
{
    return apfl_resizable_splice(
        allocator,
        elem_size,
        mem,
        len,
        cap,
        *len,
        0,
        other_mem,
        other_len
    );
}