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    /*!
    This crate defines two functions, `memchr` and `memrchr`, which expose a safe interface
    to the corresponding functions in `libc`.
    */

    #![deny(missing_docs)]
    #![allow(unused_imports)]

    extern crate libc;

    use libc::c_void;
    use libc::{c_int, size_t};

    const LO_U64: u64 = 0x0101010101010101;
    const HI_U64: u64 = 0x8080808080808080;

    // use truncation
    const LO_USIZE: usize = LO_U64 as usize;
    const HI_USIZE: usize = HI_U64 as usize;

    #[cfg(target_pointer_width = "32")]
    const USIZE_BYTES: usize = 4;
    #[cfg(target_pointer_width = "64")]
    const USIZE_BYTES: usize = 8;

    /// Return `true` if `x` contains any zero byte.
    ///
    /// From *Matters Computational*, J. Arndt
    ///
    /// "The idea is to subtract one from each of the bytes and then look for
    /// bytes where the borrow propagated all the way to the most significant
    /// bit."
    #[inline]
    fn contains_zero_byte(x: usize) -> bool {
        x.wrapping_sub(LO_USIZE) & !x & HI_USIZE != 0
    }

    #[cfg(target_pointer_width = "32")]
    #[inline]
    fn repeat_byte(b: u8) -> usize {
        let mut rep = (b as usize) << 8 | b as usize;
        rep = rep << 16 | rep;
        rep
    }

    #[cfg(target_pointer_width = "64")]
    #[inline]
    fn repeat_byte(b: u8) -> usize {
        let mut rep = (b as usize) << 8 | b as usize;
        rep = rep << 16 | rep;
        rep = rep << 32 | rep;
        rep
    }

    /// A safe interface to `memchr`.
    ///
    /// Returns the index corresponding to the first occurrence of `needle` in
    /// `haystack`, or `None` if one is not found.
    ///
    /// memchr reduces to super-optimized machine code at around an order of
    /// magnitude faster than `haystack.iter().position(|&b| b == needle)`.
    /// (See benchmarks.)
    ///
    /// # Example
    ///
    /// This shows how to find the first position of a byte in a byte string.
    ///
    /// ```rust
    /// use memchr::memchr;
    ///
    /// let haystack = b"the quick brown fox";
    /// assert_eq!(memchr(b'k', haystack), Some(8));
    /// ```
    #[inline(always)] // reduces constant overhead
    pub fn memchr(needle: u8, haystack: &[u8]) -> Option<usize> {
        // libc memchr
        #[cfg(any(not(target_os = "windows"),
                  not(any(target_pointer_width = "32",
                          target_pointer_width = "64"))))]
        #[inline(always)] // reduces constant overhead
        fn memchr_specific(needle: u8, haystack: &[u8]) -> Option<usize> {
            use libc::memchr as libc_memchr;

            let p = unsafe {
                libc_memchr(
                    haystack.as_ptr() as *const c_void,
                    needle as c_int,
                    haystack.len() as size_t)
            };
            if p.is_null() {
                None
            } else {
                Some(p as usize - (haystack.as_ptr() as usize))
            }
        }

        // use fallback on windows, since it's faster
        #[cfg(all(target_os = "windows",
                  any(target_pointer_width = "32",
                      target_pointer_width = "64")))]
        fn memchr_specific(needle: u8, haystack: &[u8]) -> Option<usize> {
            fallback::memchr(needle, haystack)
        }

        memchr_specific(needle, haystack)
    }

    /// A safe interface to `memrchr`.
    ///
    /// Returns the index corresponding to the last occurrence of `needle` in
    /// `haystack`, or `None` if one is not found.
    ///
    /// # Example
    ///
    /// This shows how to find the last position of a byte in a byte string.
    ///
    /// ```rust
    /// use memchr::memrchr;
    ///
    /// let haystack = b"the quick brown fox";
    /// assert_eq!(memrchr(b'o', haystack), Some(17));
    /// ```
    #[inline(always)] // reduces constant overhead
    pub fn memrchr(needle: u8, haystack: &[u8]) -> Option<usize> {

        #[cfg(target_os = "linux")]
        #[inline(always)] // reduces constant overhead
        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 c_void,
                    needle as c_int,
                    haystack.len() as size_t)
            };
            if p.is_null() {
                None
            } else {
                Some(p as usize - (haystack.as_ptr() as usize))
            }
        }

        #[cfg(all(not(target_os = "linux"),
                  any(target_pointer_width = "32", target_pointer_width = "64")))]
        fn memrchr_specific(needle: u8, haystack: &[u8]) -> Option<usize> {
            fallback::memrchr(needle, haystack)
        }

        // For the rare case of neither 32 bit nor 64-bit platform.
        #[cfg(all(not(target_os = "linux"),
                  not(target_pointer_width = "32"),
                  not(target_pointer_width = "64")))]
        fn memrchr_specific(needle: u8, haystack: &[u8]) -> Option<usize> {
            haystack.iter().rposition(|&b| b == needle)
        }

        memrchr_specific(needle, haystack)
    }

    /// Like `memchr`, but searches for two bytes instead of one.
    pub fn memchr2(needle1: u8, needle2: u8, haystack: &[u8]) -> Option<usize> {
        use std::cmp;

        fn slow(b1: u8, b2: u8, haystack: &[u8]) -> Option<usize> {
            haystack.iter().position(|&b| b == b1 || b == b2)
        }

        let len = haystack.len();
        let ptr = haystack.as_ptr();
        let align = (ptr as usize) & (USIZE_BYTES - 1);
        let mut i = 0;
        if align > 0 {
            i = cmp::min(USIZE_BYTES - align, len);
            if let Some(found) = slow(needle1, needle2, &haystack[..i]) {
                return Some(found);
            }
        }
        let repeated_b1 = repeat_byte(needle1);
        let repeated_b2 = repeat_byte(needle2);
        if len >= USIZE_BYTES {
            while i <= len - USIZE_BYTES {
                unsafe {
                    let u = *(ptr.offset(i as isize) as *const usize);
                    let found_ub1 = contains_zero_byte(u ^ repeated_b1);
                    let found_ub2 = contains_zero_byte(u ^ repeated_b2);
                    if found_ub1 || found_ub2 {
                        break;
                    }
                }
                i += USIZE_BYTES;
            }
        }
        slow(needle1, needle2, &haystack[i..]).map(|pos| i + pos)
    }

    /// Like `memchr`, but searches for three bytes instead of one.
    pub fn memchr3(
        needle1: u8,
        needle2: u8,
        needle3: u8,
        haystack: &[u8],
    ) -> Option<usize> {
        use std::cmp;

        fn slow(b1: u8, b2: u8, b3: u8, haystack: &[u8]) -> Option<usize> {
            haystack.iter().position(|&b| b == b1 || b == b2 || b == b3)
        }

        let len = haystack.len();
        let ptr = haystack.as_ptr();
        let align = (ptr as usize) & (USIZE_BYTES - 1);
        let mut i = 0;
        if align > 0 {
            i = cmp::min(USIZE_BYTES - align, len);
            if let Some(found) = slow(needle1, needle2, needle3, &haystack[..i]) {
                return Some(found);
            }
        }
        let repeated_b1 = repeat_byte(needle1);
        let repeated_b2 = repeat_byte(needle2);
        let repeated_b3 = repeat_byte(needle3);
        if len >= USIZE_BYTES {
            while i <= len - USIZE_BYTES {
                unsafe {
                    let u = *(ptr.offset(i as isize) as *const usize);
                    let found_ub1 = contains_zero_byte(u ^ repeated_b1);
                    let found_ub2 = contains_zero_byte(u ^ repeated_b2);
                    let found_ub3 = contains_zero_byte(u ^ repeated_b3);
                    if found_ub1 || found_ub2 || found_ub3 {
                        break;
                    }
                }
                i += USIZE_BYTES;
            }
        }
        slow(needle1, needle2, needle3, &haystack[i..]).map(|pos| i + pos)
    }

    #[allow(dead_code)]
    #[cfg(all(not(target_os = "linux"),
              any(target_pointer_width = "32", target_pointer_width = "64")))]
    mod fallback {
        use std::cmp;
        use super::{
            LO_U64, HI_U64, LO_USIZE, HI_USIZE, USIZE_BYTES,
            contains_zero_byte, repeat_byte,
        };

        /// Return the first index matching the byte `a` in `text`.
        pub fn memchr(x: u8, text: &[u8]) -> Option<usize> {
            // Scan for a single byte value by reading two `usize` words at a time.
            //
            // Split `text` in three parts
            // - unaligned inital part, before the first word aligned address in text
            // - body, scan by 2 words at a time
            // - the last remaining part, < 2 word size
            let len = text.len();
            let ptr = text.as_ptr();

            // search up to an aligned boundary
            let align = (ptr as usize) & (USIZE_BYTES - 1);
            let mut offset;
            if align > 0 {
                offset = cmp::min(USIZE_BYTES - align, len);
                if let Some(index) = text[..offset].iter().position(|elt| *elt == x) {
                    return Some(index);
                }
            } else {
                offset = 0;
            }

            // search the body of the text
            let repeated_x = repeat_byte(x);

            if len >= 2 * USIZE_BYTES {
                while offset <= len - 2 * USIZE_BYTES {
                    unsafe {
                        let u = *(ptr.offset(offset as isize) as *const usize);
                        let v = *(ptr.offset((offset + USIZE_BYTES) as isize) as *const usize);

                        // break if there is a matching byte
                        let zu = contains_zero_byte(u ^ repeated_x);
                        let zv = contains_zero_byte(v ^ repeated_x);
                        if zu || zv {
                            break;
                        }
                    }
                    offset += USIZE_BYTES * 2;
                }
            }

            // find the byte after the point the body loop stopped
            text[offset..].iter().position(|elt| *elt == x).map(|i| offset + i)
        }

        /// Return the last index matching the byte `a` in `text`.
        pub fn memrchr(x: u8, text: &[u8]) -> Option<usize> {
            // Scan for a single byte value by reading two `usize` words at a time.
            //
            // Split `text` in three parts
            // - unaligned tail, after the last word aligned address in text
            // - body, scan by 2 words at a time
            // - the first remaining bytes, < 2 word size
            let len = text.len();
            let ptr = text.as_ptr();

            // search to an aligned boundary
            let end_align = (ptr as usize + len) & (USIZE_BYTES - 1);
            let mut offset;
            if end_align > 0 {
                offset = len - cmp::min(USIZE_BYTES - end_align, len);
                if let Some(index) = text[offset..].iter().rposition(|elt| *elt == x) {
                    return Some(offset + index);
                }
            } else {
                offset = len;
            }

            // search the body of the text
            let repeated_x = repeat_byte(x);

            while offset >= 2 * USIZE_BYTES {
                unsafe {
                    let u = *(ptr.offset(offset as isize - 2 * USIZE_BYTES as isize) as *const usize);
                    let v = *(ptr.offset(offset as isize - USIZE_BYTES as isize) as *const usize);

                    // break if there is a matching byte
                    let zu = contains_zero_byte(u ^ repeated_x);
                    let zv = contains_zero_byte(v ^ repeated_x);
                    if zu || zv {
                        break;
                    }
                }
                offset -= 2 * USIZE_BYTES;
            }

            // find the byte before the point the body loop stopped
            text[..offset].iter().rposition(|elt| *elt == x)
        }
    }

    #[cfg(test)]
    mod tests {
        extern crate quickcheck;

        use super::{memchr, memrchr, memchr2, memchr3};

        #[test]
        fn matches_one() {
            assert_eq!(Some(0), memchr(b'a', b"a"));
        }

        #[test]
        fn matches_begin() {
            assert_eq!(Some(0), memchr(b'a', b"aaaa"));
        }

        #[test]
        fn matches_end() {
            assert_eq!(Some(4), memchr(b'z', b"aaaaz"));
        }

        #[test]
        fn matches_nul() {
            assert_eq!(Some(4), memchr(b'\x00', b"aaaa\x00"));
        }

        #[test]
        fn matches_past_nul() {
            assert_eq!(Some(5), memchr(b'z', b"aaaa\x00z"));
        }

        #[test]
        fn no_match_empty() {
            assert_eq!(None, memchr(b'a', b""));
        }

        #[test]
        fn no_match() {
            assert_eq!(None, memchr(b'a', b"xyz"));
        }

        #[test]
        fn qc_never_fail() {
            fn prop(needle: u8, haystack: Vec<u8>) -> bool {
                memchr(needle, &haystack); true
            }
            quickcheck::quickcheck(prop as fn(u8, Vec<u8>) -> bool);
        }

        #[test]
        fn matches_one_reversed() {
            assert_eq!(Some(0), memrchr(b'a', b"a"));
        }

        #[test]
        fn matches_begin_reversed() {
            assert_eq!(Some(3), memrchr(b'a', b"aaaa"));
        }

        #[test]
        fn matches_end_reversed() {
            assert_eq!(Some(0), memrchr(b'z', b"zaaaa"));
        }

        #[test]
        fn matches_nul_reversed() {
            assert_eq!(Some(4), memrchr(b'\x00', b"aaaa\x00"));
        }

        #[test]
        fn matches_past_nul_reversed() {
            assert_eq!(Some(0), memrchr(b'z', b"z\x00aaaa"));
        }

        #[test]
        fn no_match_empty_reversed() {
            assert_eq!(None, memrchr(b'a', b""));
        }

        #[test]
        fn no_match_reversed() {
            assert_eq!(None, memrchr(b'a', b"xyz"));
        }

        #[test]
        fn qc_never_fail_reversed() {
            fn prop(needle: u8, haystack: Vec<u8>) -> bool {
                memrchr(needle, &haystack); true
            }
            quickcheck::quickcheck(prop as fn(u8, Vec<u8>) -> bool);
        }

        #[test]
        fn memchr2_matches_one() {
            assert_eq!(Some(0), memchr2(b'a', b'b', b"a"));
            assert_eq!(Some(0), memchr2(b'a', b'b', b"b"));
            assert_eq!(Some(0), memchr2(b'b', b'a', b"a"));
            assert_eq!(Some(0), memchr2(b'b', b'a', b"b"));
        }

        #[test]
        fn memchr2_matches_begin() {
            assert_eq!(Some(0), memchr2(b'a', b'b', b"aaaa"));
            assert_eq!(Some(0), memchr2(b'a', b'b', b"bbbb"));
        }

        #[test]
        fn memchr2_matches_end() {
            assert_eq!(Some(4), memchr2(b'z', b'y', b"aaaaz"));
            assert_eq!(Some(4), memchr2(b'z', b'y', b"aaaay"));
        }

        #[test]
        fn memchr2_matches_nul() {
            assert_eq!(Some(4), memchr2(b'\x00', b'z', b"aaaa\x00"));
            assert_eq!(Some(4), memchr2(b'z', b'\x00', b"aaaa\x00"));
        }

        #[test]
        fn memchr2_matches_past_nul() {
            assert_eq!(Some(5), memchr2(b'z', b'y', b"aaaa\x00z"));
            assert_eq!(Some(5), memchr2(b'y', b'z', b"aaaa\x00z"));
        }

        #[test]
        fn memchr2_no_match_empty() {
            assert_eq!(None, memchr2(b'a', b'b', b""));
            assert_eq!(None, memchr2(b'b', b'a', b""));
        }

        #[test]
        fn memchr2_no_match() {
            assert_eq!(None, memchr2(b'a', b'b', b"xyz"));
        }

        #[test]
        fn qc_never_fail_memchr2() {
            fn prop(needle1: u8, needle2: u8, haystack: Vec<u8>) -> bool {
                memchr2(needle1, needle2, &haystack); true
            }
            quickcheck::quickcheck(prop as fn(u8, u8, Vec<u8>) -> bool);
        }

        #[test]
        fn memchr3_matches_one() {
            assert_eq!(Some(0), memchr3(b'a', b'b', b'c', b"a"));
            assert_eq!(Some(0), memchr3(b'a', b'b', b'c', b"b"));
            assert_eq!(Some(0), memchr3(b'a', b'b', b'c', b"c"));
        }

        #[test]
        fn memchr3_matches_begin() {
            assert_eq!(Some(0), memchr3(b'a', b'b', b'c', b"aaaa"));
            assert_eq!(Some(0), memchr3(b'a', b'b', b'c', b"bbbb"));
            assert_eq!(Some(0), memchr3(b'a', b'b', b'c', b"cccc"));
        }

        #[test]
        fn memchr3_matches_end() {
            assert_eq!(Some(4), memchr3(b'z', b'y', b'x', b"aaaaz"));
            assert_eq!(Some(4), memchr3(b'z', b'y', b'x', b"aaaay"));
            assert_eq!(Some(4), memchr3(b'z', b'y', b'x', b"aaaax"));
        }

        #[test]
        fn memchr3_matches_nul() {
            assert_eq!(Some(4), memchr3(b'\x00', b'z', b'y', b"aaaa\x00"));
            assert_eq!(Some(4), memchr3(b'z', b'\x00', b'y', b"aaaa\x00"));
            assert_eq!(Some(4), memchr3(b'z', b'y', b'\x00', b"aaaa\x00"));
        }

        #[test]
        fn memchr3_matches_past_nul() {
            assert_eq!(Some(5), memchr3(b'z', b'y', b'x', b"aaaa\x00z"));
            assert_eq!(Some(5), memchr3(b'y', b'z', b'x', b"aaaa\x00z"));
            assert_eq!(Some(5), memchr3(b'y', b'x', b'z', b"aaaa\x00z"));
        }

        #[test]
        fn memchr3_no_match_empty() {
            assert_eq!(None, memchr3(b'a', b'b', b'c', b""));
            assert_eq!(None, memchr3(b'b', b'a', b'c', b""));
            assert_eq!(None, memchr3(b'c', b'b', b'a', b""));
        }

        #[test]
        fn memchr3_no_match() {
            assert_eq!(None, memchr3(b'a', b'b', b'c', b"xyz"));
        }

        #[test]
        fn qc_never_fail_memchr3() {
            fn prop(
                needle1: u8,
                needle2: u8,
                needle3: u8,
                haystack: Vec<u8>,
            ) -> bool {
                memchr3(needle1, needle2, needle3, &haystack); true
            }
            quickcheck::quickcheck(prop as fn(u8, u8, u8, Vec<u8>) -> bool);
        }

        #[test]
        fn qc_correct_memchr() {
            fn prop(v: Vec<u8>, offset: u8) -> bool {
                // test all pointer alignments
                let uoffset = (offset & 0xF) as usize;
                let data = if uoffset <= v.len() {
                    &v[uoffset..]
                } else {
                    &v[..]
                };
                for byte in 0..256u32 {
                    let byte = byte as u8;
                    if memchr(byte, &data) != data.iter().position(|elt| *elt == byte) {
                        return false;
                    }
                }
                true
            }
            quickcheck::quickcheck(prop as fn(Vec<u8>, u8) -> bool);
        }

        #[test]
        fn qc_correct_memrchr() {
            fn prop(v: Vec<u8>, offset: u8) -> bool {
                // test all pointer alignments
                let uoffset = (offset & 0xF) as usize;
                let data = if uoffset <= v.len() {
                    &v[uoffset..]
                } else {
                    &v[..]
                };
                for byte in 0..256u32 {
                    let byte = byte as u8;
                    if memrchr(byte, &data) != data.iter().rposition(|elt| *elt == byte) {
                        return false;
                    }
                }
                true
            }
            quickcheck::quickcheck(prop as fn(Vec<u8>, u8) -> bool);
        }

        #[test]
        fn qc_correct_memchr2() {
            fn prop(v: Vec<u8>, offset: u8) -> bool {
                // test all pointer alignments
                let uoffset = (offset & 0xF) as usize;
                let data = if uoffset <= v.len() {
                    &v[uoffset..]
                } else {
                    &v[..]
                };
                for b1 in 0..256u32 {
                    for b2 in 0..256u32 {
                        let (b1, b2) = (b1 as u8, b2 as u8);
                        let expected =
                            data.iter().position(|&b| b == b1 || b == b2);
                        let got = memchr2(b1, b2, &data);
                        if expected != got {
                            return false;
                        }
                    }
                }
                true
            }
            quickcheck::quickcheck(prop as fn(Vec<u8>, u8) -> bool);
        }
    }

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