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    // Original implementation taken from rust-memchr.
    // Copyright 2015 Andrew Gallant, bluss and Nicolas Koch

    pub fn memchr(needle: u8, haystack: &[u8]) -> Option<usize> {
        let p = unsafe {
            libc::memchr(
                haystack.as_ptr() as *const libc::c_void,
                needle as libc::c_int,
                haystack.len(),
            )
        };
        if p.is_null() { None } else { Some(p as usize - (haystack.as_ptr() as usize)) }
    }

    pub fn memrchr(needle: u8, haystack: &[u8]) -> Option<usize> {
        #[cfg(target_os = "linux")]
        fn memrchr_specific(needle: u8, haystack: &[u8]) -> Option<usize> {
            // GNU's memrchr() will - unlike memchr() - error if haystack is empty.
            if haystack.is_empty() {
                return None;
            }
            let p = unsafe {
                libc::memrchr(
                    haystack.as_ptr() as *const libc::c_void,
                    needle as libc::c_int,
                    haystack.len(),
                )
            };
            if p.is_null() { None } else { Some(p as usize - (haystack.as_ptr() as usize)) }
        }

        #[cfg(not(target_os = "linux"))]
        fn memrchr_specific(needle: u8, haystack: &[u8]) -> Option<usize> {
            core::slice::memchr::memrchr(needle, haystack)
        }

        memrchr_specific(needle, haystack)
    }