RedBear-OS/src/header/string/mod.rs

//! `string.h` implementation.
//!
//! See <https://pubs.opengroup.org/onlinepubs/9799919799/basedefs/string.h.html>.

use core::{
    iter::{once, zip},
    mem::{self, MaybeUninit},
    ptr, slice, usize,
};

use cbitset::BitSet256;

use crate::{
    header::{errno::*, signal},
    iter::{NulTerminated, NulTerminatedInclusive, SrcDstPtrIter},
    platform::{self, types::*},
};

/// See <https://pubs.opengroup.org/onlinepubs/9799919799/functions/memccpy.html>.
#[no_mangle]
pub unsafe extern "C" fn memccpy(
    dest: *mut c_void,
    src: *const c_void,
    c: c_int,
    n: size_t,
) -> *mut c_void {
    let to = memchr(src, c, n);
    if to.is_null() {
        return to;
    }
    let dist = (to as usize) - (src as usize);
    if memcpy(dest, src, dist).is_null() {
        return ptr::null_mut();
    }
    (dest as *mut u8).add(dist + 1) as *mut c_void
}

/// See <https://pubs.opengroup.org/onlinepubs/9799919799/functions/memchr.html>.
#[no_mangle]
pub unsafe extern "C" fn memchr(
    haystack: *const c_void,
    needle: c_int,
    len: size_t,
) -> *mut c_void {
    let haystack = slice::from_raw_parts(haystack as *const u8, len as usize);

    match memchr::memchr(needle as u8, haystack) {
        Some(index) => haystack[index..].as_ptr() as *mut c_void,
        None => ptr::null_mut(),
    }
}

/// See <https://pubs.opengroup.org/onlinepubs/9799919799/functions/memcmp.html>.
#[no_mangle]
#[no_mangle]
pub unsafe extern "C" fn memcmp(s1: *const c_void, s2: *const c_void, n: usize) -> c_int {
    let (div, rem) = (n / mem::size_of::<usize>(), n % mem::size_of::<usize>());
    let mut a = s1 as *const usize;
    let mut b = s2 as *const usize;
    for _ in 0..div {
        if *a != *b {
            for i in 0..mem::size_of::<usize>() {
                let c = *(a as *const u8).add(i);
                let d = *(b as *const u8).add(i);
                if c != d {
                    return c as c_int - d as c_int;
                }
            }
            unreachable!()
        }
        a = a.offset(1);
        b = b.offset(1);
    }

    let mut a = a as *const u8;
    let mut b = b as *const u8;
    for _ in 0..rem {
        if *a != *b {
            return *a as c_int - *b as c_int;
        }
        a = a.offset(1);
        b = b.offset(1);
    }
    0
}

/// See <https://pubs.opengroup.org/onlinepubs/9799919799/functions/memcpy.html>.
///
/// # Safety
/// The caller must ensure that *either*:
/// - `n` is 0, *or*
///     - `s1` is convertible to a `&mut [MaybeUninit<u8>]` with length `n`,
///       and
///     - `s2` is convertible to a `&[MaybeUninit<u8>]` with length `n`.
#[no_mangle]
pub unsafe extern "C" fn memcpy(s1: *mut c_void, s2: *const c_void, n: size_t) -> *mut c_void {
    // Avoid creating slices for n == 0. This is because we are required to
    // avoid UB for n == 0, even if either s1 or s2 is null, to comply with the
    // expectations of Rust's core library, as well as C2y (N3322).
    // See https://doc.rust-lang.org/core/index.html for details.
    if n != 0 {
        // SAFETY: the caller is required to ensure that the provided pointers
        // are valid. The slices are required to have a length of at most
        // isize::MAX; this implicitly ensured by requiring valid pointers to
        // two nonoverlapping slices.
        let s1_slice = unsafe { slice::from_raw_parts_mut(s1.cast::<MaybeUninit<u8>>(), n) };
        let s2_slice = unsafe { slice::from_raw_parts(s2.cast::<MaybeUninit<u8>>(), n) };

        // At this point, it may seem tempting to use
        // s1_slice.copy_from_slice(s2_slice) here, but memcpy is one of the
        // handful of symbols whose existence is assumed by Rust's core
        // library, and thus we need to be careful here not to rely on any
        // function that calls memcpy internally.
        // See https://doc.rust-lang.org/core/index.html for details.
        //
        // Instead, we check the alignment of the two slices and try to
        // identify the largest Rust primitive type that is well-aligned for
        // copying in chunks. s1_slice and s2_slice will be divided into
        // (prefix, middle, suffix), where only the "middle" part is copyable
        // using the larger primitive type.
        let s1_addr = s1.addr();
        let s2_addr = s2.addr();
        // Find the number of similar trailing bits in the two addresses to let
        // us find the largest possible chunk size
        let equal_trailing_bits_count = (s1_addr ^ s2_addr).trailing_zeros();
        let chunk_size = match equal_trailing_bits_count {
            0 => 1,
            1 => 2,
            2 => 4,
            3 => 8,
            _ => 16, // use u128 chunks for any higher alignments
        };
        let chunk_align_offset = s1.align_offset(chunk_size);
        let prefix_len = chunk_align_offset.min(n);

        // Copy "prefix" bytes
        for (s1_elem, s2_elem) in zip(&mut s1_slice[..prefix_len], &s2_slice[..prefix_len]) {
            *s1_elem = *s2_elem;
        }

        if chunk_align_offset < n {
            fn copy_chunks_and_remainder<const N: usize, T: Copy>(
                dst: &mut [MaybeUninit<u8>],
                src: &[MaybeUninit<u8>],
            ) {
                // Check sanity
                assert_eq!(N, mem::size_of::<T>());
                assert_eq!(0, N % mem::align_of::<T>());
                assert!(dst.as_mut_ptr().is_aligned_to(N));
                assert!(src.as_ptr().is_aligned_to(N));

                // Split into "middle" and "suffix"
                let (dst_chunks, dst_remainder) = dst.as_chunks_mut::<N>();
                let (src_chunks, src_remainder) = src.as_chunks::<N>();

                // Copy "middle"
                for (dst_chunk, src_chunk) in zip(dst_chunks, src_chunks) {
                    // SAFETY: the chunks are safely subsliced from s1 and
                    // s2. Alignment is ensured through the use of
                    // "align_offset", while the size of the chunks is
                    // explicitly taken to match the primitive size.
                    let dst_chunk_primitive: &mut MaybeUninit<T> =
                        unsafe { &mut *dst_chunk.as_mut_ptr().cast() };
                    let src_chunk_primitive: &MaybeUninit<T> =
                        unsafe { &*src_chunk.as_ptr().cast() };
                    *dst_chunk_primitive = *src_chunk_primitive;
                }

                // Copy "suffix"
                for (dst_elem, src_elem) in zip(dst_remainder, src_remainder) {
                    *dst_elem = *src_elem;
                }
            }

            // Copy "middle" bytes (if length is sufficient) and any remaining
            // "suffix" bytes.
            let s1_middle_and_suffix = &mut s1_slice[prefix_len..];
            let s2_middle_and_suffix = &s2_slice[prefix_len..];
            match chunk_size {
                1 => {
                    for (s1_elem, s2_elem) in zip(s1_middle_and_suffix, s2_middle_and_suffix) {
                        *s1_elem = *s2_elem;
                    }
                }
                2 => {
                    copy_chunks_and_remainder::<2, u16>(s1_middle_and_suffix, s2_middle_and_suffix)
                }
                4 => {
                    copy_chunks_and_remainder::<4, u32>(s1_middle_and_suffix, s2_middle_and_suffix)
                }
                8 => {
                    copy_chunks_and_remainder::<8, u64>(s1_middle_and_suffix, s2_middle_and_suffix)
                }
                16 => copy_chunks_and_remainder::<16, u128>(
                    s1_middle_and_suffix,
                    s2_middle_and_suffix,
                ),
                _ => unreachable!(),
            }
        }
    }

    s1
}

/// See <https://pubs.opengroup.org/onlinepubs/9799919799/functions/memmem.html>.
///
/// # Safety
/// The caller must ensure that:
/// - `haystack` is convertible to a `&[u8]` with length `haystacklen`, and
/// - `needle` is convertible to a `&[u8]` with length `needlelen`.
#[no_mangle]
pub unsafe extern "C" fn memmem(
    haystack: *const c_void,
    haystacklen: size_t,
    needle: *const c_void,
    needlelen: size_t,
) -> *mut c_void {
    match needlelen {
        // Required to satisfy spec (would otherwise cause .windows() to panic)
        0 => haystack,
        _ => {
            // SAFETY: the caller is required to ensure that the provided
            // pointers are valid.
            let haystack_slice =
                unsafe { slice::from_raw_parts(haystack.cast::<u8>(), haystacklen) };
            let needle_slice = unsafe { slice::from_raw_parts(needle.cast::<u8>(), needlelen) };

            // At this point, .windows() will receive a nonzero `needlelen` and
            // thus not panic.
            match haystack_slice
                .windows(needlelen)
                .find(|&haystack_window| haystack_window == needle_slice)
            {
                Some(match_slice) => match_slice.as_ptr().cast(),
                None => ptr::null(),
            }
        }
    }
    .cast_mut()
}

/// See <https://pubs.opengroup.org/onlinepubs/9799919799/functions/memmove.html>.
#[no_mangle]
pub unsafe extern "C" fn memmove(s1: *mut c_void, s2: *const c_void, n: size_t) -> *mut c_void {
    if s2 < s1 as *const c_void {
        // copy from end
        let mut i = n;
        while i != 0 {
            i -= 1;
            *(s1 as *mut u8).add(i) = *(s2 as *const u8).add(i);
        }
    } else {
        // copy from beginning
        let mut i = 0;
        while i < n {
            *(s1 as *mut u8).add(i) = *(s2 as *const u8).add(i);
            i += 1;
        }
    }
    s1
}

/// Non-POSIX, see <https://www.man7.org/linux/man-pages/man3/memchr.3.html>.
#[no_mangle]
pub unsafe extern "C" fn memrchr(
    haystack: *const c_void,
    needle: c_int,
    len: size_t,
) -> *mut c_void {
    let haystack = slice::from_raw_parts(haystack as *const u8, len as usize);

    match memchr::memrchr(needle as u8, haystack) {
        Some(index) => haystack[index..].as_ptr() as *mut c_void,
        None => ptr::null_mut(),
    }
}

/// See <https://pubs.opengroup.org/onlinepubs/9799919799/functions/memset.html>.
#[no_mangle]
pub unsafe extern "C" fn memset(s: *mut c_void, c: c_int, n: size_t) -> *mut c_void {
    for i in 0..n {
        *(s as *mut u8).add(i) = c as u8;
    }
    s
}

/// See <https://pubs.opengroup.org/onlinepubs/9799919799/functions/strcpy.html>.
#[no_mangle]
pub unsafe extern "C" fn stpcpy(mut s1: *mut c_char, mut s2: *const c_char) -> *mut c_char {
    loop {
        *s1 = *s2;

        if *s1 == 0 {
            break;
        }

        s1 = s1.add(1);
        s2 = s2.add(1);
    }

    s1
}

/// See <https://pubs.opengroup.org/onlinepubs/9799919799/functions/strncpy.html>.
#[no_mangle]
pub unsafe extern "C" fn stpncpy(
    mut s1: *mut c_char,
    mut s2: *const c_char,
    mut n: size_t,
) -> *mut c_char {
    while n > 0 {
        *s1 = *s2;

        if *s1 == 0 {
            break;
        }

        n -= 1;
        s1 = s1.add(1);
        s2 = s2.add(1);
    }

    memset(s1.cast(), 0, n);

    s1
}

/// Non-POSIX, see <https://www.man7.org/linux/man-pages/man3/strstr.3.html>.
#[no_mangle]
pub unsafe extern "C" fn strcasestr(haystack: *const c_char, needle: *const c_char) -> *mut c_char {
    inner_strstr(haystack, needle, !32)
}

/// See <https://pubs.opengroup.org/onlinepubs/9799919799/functions/strcat.html>.
#[no_mangle]
pub unsafe extern "C" fn strcat(s1: *mut c_char, s2: *const c_char) -> *mut c_char {
    strncat(s1, s2, usize::MAX)
}

/// See <https://pubs.opengroup.org/onlinepubs/9799919799/functions/strchr.html>.
///
/// # Safety
/// The caller is required to ensure that `s` is a valid pointer to a buffer
/// containing at least one nul value. The pointed-to buffer must not be
/// modified for the duration of the call.
#[no_mangle]
pub unsafe extern "C" fn strchr(mut s: *const c_char, c: c_int) -> *mut c_char {
    let c_as_c_char = c as c_char;

    // We iterate over non-mut references and thus need to coerce the
    // resulting reference via a *const pointer before we can get our *mut.
    // SAFETY: the caller is required to ensure that s points to a valid
    // nul-terminated buffer.
    let ptr: *const c_char =
        match unsafe { NulTerminatedInclusive::new(s) }.find(|&&sc| sc == c_as_c_char) {
            Some(sc_ref) => sc_ref,
            None => ptr::null(),
        };
    ptr.cast_mut()
}

/// Non-POSIX, see <https://man7.org/linux/man-pages/man3/strchr.3.html>.
#[no_mangle]
pub unsafe extern "C" fn strchrnul(s: *const c_char, c: c_int) -> *mut c_char {
    let mut s = s.cast_mut();
    loop {
        if *s == c as _ {
            break;
        }
        if *s == 0 {
            break;
        }
        s = s.add(1);
    }
    s
}

/// See <https://pubs.opengroup.org/onlinepubs/9799919799/functions/strcmp.html>.
#[no_mangle]
pub unsafe extern "C" fn strcmp(s1: *const c_char, s2: *const c_char) -> c_int {
    strncmp(s1, s2, usize::MAX)
}

/// See <https://pubs.opengroup.org/onlinepubs/9799919799/functions/strcoll.html>.
#[no_mangle]
pub unsafe extern "C" fn strcoll(s1: *const c_char, s2: *const c_char) -> c_int {
    // relibc has no locale stuff (yet)
    strcmp(s1, s2)
}

// TODO: strcoll_l

/// See <https://pubs.opengroup.org/onlinepubs/9799919799/functions/strcpy.html>.
#[no_mangle]
pub unsafe extern "C" fn strcpy(dst: *mut c_char, src: *const c_char) -> *mut c_char {
    let src_iter = unsafe { NulTerminated::new(src) };
    let src_dest_iter = unsafe { SrcDstPtrIter::new(src_iter.chain(once(&0)), dst) };
    for (src_item, dst_item) in src_dest_iter {
        dst_item.write(*src_item);
    }

    dst
}

pub unsafe fn inner_strspn(s1: *const c_char, s2: *const c_char, cmp: bool) -> size_t {
    let mut s1 = s1 as *const u8;
    let mut s2 = s2 as *const u8;

    // The below logic is effectively ripped from the musl implementation. It
    // works by placing each byte as it's own bit in an array of numbers. Each
    // number can hold up to 8 * mem::size_of::<usize>() bits. We need 256 bits
    // in total, to fit one byte.

    let mut set = BitSet256::new();

    while *s2 != 0 {
        set.insert(*s2 as usize);
        s2 = s2.offset(1);
    }

    let mut i = 0;
    while *s1 != 0 {
        if set.contains(*s1 as usize) != cmp {
            break;
        }
        i += 1;
        s1 = s1.offset(1);
    }
    i
}

/// See <https://pubs.opengroup.org/onlinepubs/9799919799/functions/strcspn.html>.
#[no_mangle]
pub unsafe extern "C" fn strcspn(s1: *const c_char, s2: *const c_char) -> size_t {
    inner_strspn(s1, s2, false)
}

/// See <https://pubs.opengroup.org/onlinepubs/9799919799/functions/strdup.html>.
#[no_mangle]
pub unsafe extern "C" fn strdup(s1: *const c_char) -> *mut c_char {
    strndup(s1, usize::MAX)
}

/// See <https://pubs.opengroup.org/onlinepubs/9799919799/functions/strerror.html>.
#[no_mangle]
pub unsafe extern "C" fn strerror(errnum: c_int) -> *mut c_char {
    use core::fmt::Write;

    static mut strerror_buf: [u8; 256] = [0; 256];

    let mut w = platform::StringWriter(strerror_buf.as_mut_ptr(), strerror_buf.len());

    if errnum >= 0 && errnum < STR_ERROR.len() as c_int {
        let _ = w.write_str(STR_ERROR[errnum as usize]);
    } else {
        let _ = w.write_fmt(format_args!("Unknown error {}", errnum));
    }

    strerror_buf.as_mut_ptr() as *mut c_char
}

// TODO: strerror_l

/// See <https://pubs.opengroup.org/onlinepubs/9799919799/functions/strerror.html>.
#[no_mangle]
pub unsafe extern "C" fn strerror_r(errnum: c_int, buf: *mut c_char, buflen: size_t) -> c_int {
    let msg = strerror(errnum);
    let len = strlen(msg);

    if len >= buflen {
        if buflen != 0 {
            memcpy(buf as *mut c_void, msg as *const c_void, buflen - 1);
            *buf.add(buflen - 1) = 0;
        }
        return ERANGE as c_int;
    }
    memcpy(buf as *mut c_void, msg as *const c_void, len + 1);

    0
}

/// See <https://pubs.opengroup.org/onlinepubs/9799919799/functions/strlcat.html>.
#[no_mangle]
pub unsafe extern "C" fn strlcat(dst: *mut c_char, src: *const c_char, n: size_t) -> size_t {
    let len = strlen(dst) as isize;
    let d = dst.offset(len);

    strlcpy(d, src, n)
}

#[no_mangle]
pub unsafe extern "C" fn strsep(str_: *mut *mut c_char, sep: *const c_char) -> *mut c_char {
    let s = *str_;
    if s.is_null() {
        return ptr::null_mut();
    }
    let mut end = s.add(strcspn(s, sep));
    if *end != 0 {
        *end = 0;
        end = end.add(1);
    } else {
        end = ptr::null_mut();
    }
    *str_ = end;
    s
}

/// See <https://pubs.opengroup.org/onlinepubs/9799919799/functions/strlcat.html>.
#[no_mangle]
pub unsafe extern "C" fn strlcpy(dst: *mut c_char, src: *const c_char, n: size_t) -> size_t {
    let mut i = 0;

    while *src.add(i) != 0 && i < n {
        *dst.add(i) = *src.add(i);
        i += 1;
    }

    *dst.add(i) = 0;

    i as size_t
}

/// See <https://pubs.opengroup.org/onlinepubs/9799919799/functions/strlen.html>.
#[no_mangle]
pub unsafe extern "C" fn strlen(s: *const c_char) -> size_t {
    unsafe { NulTerminated::new(s) }.count()
}

/// See <https://pubs.opengroup.org/onlinepubs/9799919799/functions/strncat.html>.
#[no_mangle]
pub unsafe extern "C" fn strncat(s1: *mut c_char, s2: *const c_char, n: size_t) -> *mut c_char {
    let len = strlen(s1.cast());
    let mut i = 0;
    while i < n {
        let b = *s2.add(i);
        if b == 0 {
            break;
        }

        *s1.add(len + i) = b;
        i += 1;
    }
    *s1.add(len + i) = 0;

    s1
}

/// See <https://pubs.opengroup.org/onlinepubs/9799919799/functions/strncmp.html>.
#[no_mangle]
pub unsafe extern "C" fn strncmp(s1: *const c_char, s2: *const c_char, n: size_t) -> c_int {
    let s1 = slice::from_raw_parts(s1 as *const c_uchar, n);
    let s2 = slice::from_raw_parts(s2 as *const c_uchar, n);

    for (&a, &b) in s1.iter().zip(s2.iter()) {
        let val = (a as c_int) - (b as c_int);
        if a != b || a == 0 {
            return val;
        }
    }

    0
}

/// See <https://pubs.opengroup.org/onlinepubs/9799919799/functions/strncpy.html>.
#[no_mangle]
pub unsafe extern "C" fn strncpy(s1: *mut c_char, s2: *const c_char, n: size_t) -> *mut c_char {
    stpncpy(s1, s2, n);
    s1
}

/// See <https://pubs.opengroup.org/onlinepubs/9799919799/functions/strdup.html>.
#[no_mangle]
pub unsafe extern "C" fn strndup(s1: *const c_char, size: size_t) -> *mut c_char {
    let len = strnlen(s1, size);

    // the "+ 1" is to account for the NUL byte
    let buffer = platform::alloc(len + 1) as *mut c_char;
    if buffer.is_null() {
        platform::ERRNO.set(ENOMEM as c_int);
    } else {
        //memcpy(buffer, s1, len)
        for i in 0..len {
            *buffer.add(i) = *s1.add(i);
        }
        *buffer.add(len) = 0;
    }

    buffer
}

/// See <https://pubs.opengroup.org/onlinepubs/9799919799/functions/strlen.html>.
#[no_mangle]
pub unsafe extern "C" fn strnlen(s: *const c_char, size: size_t) -> size_t {
    unsafe { NulTerminated::new(s) }.take(size).count()
}

/// Non-POSIX, see <https://en.cppreference.com/w/c/string/byte/strlen>.
#[no_mangle]
pub unsafe extern "C" fn strnlen_s(s: *const c_char, size: size_t) -> size_t {
    if s.is_null() {
        0
    } else {
        strnlen(s, size)
    }
}

/// See <https://pubs.opengroup.org/onlinepubs/9799919799/functions/strpbrk.html>.
#[no_mangle]
pub unsafe extern "C" fn strpbrk(s1: *const c_char, s2: *const c_char) -> *mut c_char {
    let p = s1.add(strcspn(s1, s2));
    if *p != 0 {
        p as *mut c_char
    } else {
        ptr::null_mut()
    }
}

/// See <https://pubs.opengroup.org/onlinepubs/9799919799/functions/strrchr.html>.
#[no_mangle]
pub unsafe extern "C" fn strrchr(s: *const c_char, c: c_int) -> *mut c_char {
    let len = strlen(s) as isize;
    let c = c as i8;
    let mut i = len - 1;
    while i >= 0 {
        if *s.offset(i) == c {
            return s.offset(i) as *mut c_char;
        }
        i -= 1;
    }
    ptr::null_mut()
}

/// See <https://pubs.opengroup.org/onlinepubs/9799919799/functions/strsignal.html>.
#[no_mangle]
pub unsafe extern "C" fn strsignal(sig: c_int) -> *mut c_char {
    signal::SIGNAL_STRINGS
        .get(sig as usize)
        .unwrap_or(&signal::SIGNAL_STRINGS[0]) // Unknown signal message
        .as_ptr() as *mut c_char
}

/// See <https://pubs.opengroup.org/onlinepubs/9799919799/functions/strspn.html>.
#[no_mangle]
pub unsafe extern "C" fn strspn(s1: *const c_char, s2: *const c_char) -> size_t {
    inner_strspn(s1, s2, true)
}

unsafe fn inner_strstr(
    mut haystack: *const c_char,
    needle: *const c_char,
    mask: c_char,
) -> *mut c_char {
    while *haystack != 0 {
        let mut i = 0;
        loop {
            if *needle.offset(i) == 0 {
                // We reached the end of the needle, everything matches this far
                return haystack as *mut c_char;
            }
            if *haystack.offset(i) & mask != *needle.offset(i) & mask {
                break;
            }

            i += 1;
        }

        haystack = haystack.offset(1);
    }
    ptr::null_mut()
}

/// See <https://pubs.opengroup.org/onlinepubs/9799919799/functions/strstr.html>.
#[no_mangle]
pub unsafe extern "C" fn strstr(haystack: *const c_char, needle: *const c_char) -> *mut c_char {
    inner_strstr(haystack, needle, !0)
}

/// See <https://pubs.opengroup.org/onlinepubs/9799919799/functions/strtok.html>.
#[no_mangle]
pub unsafe extern "C" fn strtok(s1: *mut c_char, delimiter: *const c_char) -> *mut c_char {
    static mut HAYSTACK: *mut c_char = ptr::null_mut();
    strtok_r(s1, delimiter, &mut HAYSTACK)
}

/// See <https://pubs.opengroup.org/onlinepubs/9799919799/functions/strtok.html>.
#[no_mangle]
pub unsafe extern "C" fn strtok_r(
    s: *mut c_char,
    delimiter: *const c_char,
    lasts: *mut *mut c_char,
) -> *mut c_char {
    // Loosely based on GLIBC implementation
    let mut haystack = s;
    if haystack.is_null() {
        if (*lasts).is_null() {
            return ptr::null_mut();
        }
        haystack = *lasts;
    }

    // Skip past any extra delimiter left over from previous call
    haystack = haystack.add(strspn(haystack, delimiter));
    if *haystack == 0 {
        *lasts = ptr::null_mut();
        return ptr::null_mut();
    }

    // Build token by injecting null byte into delimiter
    let token = haystack;
    haystack = strpbrk(token, delimiter);
    if !haystack.is_null() {
        haystack.write(0);
        haystack = haystack.add(1);
        *lasts = haystack;
    } else {
        *lasts = ptr::null_mut();
    }

    token
}

/// See <https://pubs.opengroup.org/onlinepubs/9799919799/functions/strxfrm.html>.
#[no_mangle]
pub unsafe extern "C" fn strxfrm(s1: *mut c_char, s2: *const c_char, n: size_t) -> size_t {
    // relibc has no locale stuff (yet)
    let len = strlen(s2);
    if len < n {
        strcpy(s1, s2);
    }
    len
}

// TODO: strxfrm_l