mesh-loader 0.1.13

Fast parser for 3D-model-formats.
Documentation 
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#[cfg(feature = "obj")]
use std::{borrow::Cow, ffi::OsStr, path::Path, str};

// This is the same as s.starts_with(needle), but faster if the length of the
// needle is known at compile time.
#[inline(always)] // Ensure the code getting the length of the needle is inlined.
pub(crate) fn starts_with(mut s: &[u8], mut needle: &'static [u8]) -> bool {
    if s.len() < needle.len() {
        return false;
    }
    if needle.len() < 4 {
        return s.starts_with(needle);
    }
    if needle.len() < 8 {
        // u32 (4 bytes) + 0-3 bytes
        return u32::from_ne_bytes(needle[..4].try_into().unwrap())
            == u32::from_ne_bytes(s[..4].try_into().unwrap())
            && s[4..].starts_with(&needle[4..]);
    }
    if needle.len() < 12 {
        // u64 (8 bytes) + 0-3 bytes
        return u64::from_ne_bytes(needle[..8].try_into().unwrap())
            == u64::from_ne_bytes(s[..8].try_into().unwrap())
            && s[8..].starts_with(&needle[8..]);
    }
    if needle.len() < 16 {
        // u64 (8 bytes) + u32 (4 bytes) + 0-3 bytes
        return u64::from_ne_bytes(needle[..8].try_into().unwrap())
            == u64::from_ne_bytes(s[..8].try_into().unwrap())
            && u32::from_ne_bytes(needle[8..12].try_into().unwrap())
                == u32::from_ne_bytes(s[8..12].try_into().unwrap())
            && s[12..].starts_with(&needle[12..]);
    }
    // u64 (8 bytes) + u64 (8 bytes) + N bytes
    while needle.len() >= 8 {
        if u64::from_ne_bytes(needle[..8].try_into().unwrap())
            != u64::from_ne_bytes(s[..8].try_into().unwrap())
        {
            return false;
        }
        needle = &needle[8..];
        s = &s[8..];
    }
    s.starts_with(needle)
}

#[cfg(any(feature = "collada", feature = "obj"))]
#[inline]
pub(crate) const fn memchr_naive(needle: u8, mut s: &[u8]) -> Option<usize> {
    let start = s;
    while let Some((&b, s_next)) = s.split_first() {
        if b == needle {
            return Some(start.len() - s.len());
        }
        s = s_next;
    }
    None
}

#[cfg(any(feature = "obj", feature = "stl"))]
#[inline]
pub(crate) const fn memchr_naive_table(
    needle_mask: u8,
    table: &[u8; 256],
    mut s: &[u8],
) -> Option<usize> {
    let start = s;
    while let Some((&b, s_next)) = s.split_first() {
        if table[b as usize] & needle_mask != 0 {
            return Some(start.len() - s.len());
        }
        s = s_next;
    }
    None
}

#[cfg(any(feature = "obj", feature = "stl"))]
#[inline]
pub(crate) const fn memrchr_naive(needle: u8, mut s: &[u8]) -> Option<usize> {
    let start = s;
    while let Some((&b, s_next)) = s.split_last() {
        if b == needle {
            return Some(start.len() - s.len());
        }
        s = s_next;
    }
    None
}

#[cfg(any(feature = "obj", feature = "stl"))]
#[inline]
pub(crate) const fn bytecount_naive(needle: u8, mut s: &[u8]) -> usize {
    let mut n = 0;
    while let Some((&b, s_next)) = s.split_first() {
        n += (b == needle) as usize;
        s = s_next;
    }
    n
}

#[cfg(feature = "obj")]
#[allow(clippy::unnecessary_wraps)] // clippy bug: this lint doesn't consider cfg attribute
pub(crate) fn os_str_from_bytes(bytes: &[u8]) -> Result<&OsStr, std::str::Utf8Error> {
    #[cfg(any(unix, target_os = "wasi"))]
    {
        #[cfg(unix)]
        use std::os::unix::ffi::OsStrExt as _;
        #[cfg(target_os = "wasi")]
        use std::os::wasi::ffi::OsStrExt as _;
        Ok(OsStr::from_bytes(bytes))
    }
    #[cfg(not(any(unix, target_os = "wasi")))]
    {
        std::str::from_utf8(bytes).map(OsStr::new)
    }
}
#[cfg(feature = "obj")]
pub(crate) fn path_from_bytes(bytes: &[u8]) -> Result<&Path, std::str::Utf8Error> {
    os_str_from_bytes(bytes).map(Path::new)
}

// Ideally, we want to use Utf8Chunks here, but it is unstable.
#[cfg(feature = "obj")]
#[inline]
pub(crate) fn from_utf8_lossy(mut bytes: &[u8]) -> Cow<'_, str> {
    let mut base = String::new();
    loop {
        match str::from_utf8(bytes) {
            Ok(s) => {
                if base.is_empty() {
                    return s.into();
                }
                base.push_str(s);
                return base.into();
            }
            Err(e) => {
                let valid_up_to = e.valid_up_to();
                let s = str::from_utf8(&bytes[..valid_up_to]).unwrap();
                base.push_str(s);
                base.push(char::REPLACEMENT_CHARACTER);
                if let Some(error_len) = e.error_len() {
                    bytes = &bytes[valid_up_to + error_len..];
                } else {
                    return base.into();
                }
            }
        }
    }
}