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    /*!
    This is the Teddy searcher, but ported to AVX2.

    See the module comments in the SSSE3 Teddy searcher for a more in depth
    explanation of how this algorithm works. For the most part, this port is
    basically the same as the SSSE3 version, but using 256-bit vectors instead of
    128-bit vectors, which increases throughput.
    */

    use std::cmp;

    use aho_corasick::{self, AhoCorasick, AhoCorasickBuilder};
    use syntax::hir::literal::Literals;

    use vector::avx2::{AVX2VectorBuilder, u8x32};

    /// Corresponds to the number of bytes read at a time in the haystack.
    const BLOCK_SIZE: usize = 32;

    /// Match reports match information.
    #[derive(Debug, Clone)]
    pub struct Match {
        /// The index of the pattern that matched. The index is in correspondence
        /// with the order of the patterns given at construction.
        pub pat: usize,
        /// The start byte offset of the match.
        pub start: usize,
        /// The end byte offset of the match. This is always `start + pat.len()`.
        pub end: usize,
    }

    /// A SIMD accelerated multi substring searcher.
    #[derive(Debug, Clone)]
    pub struct Teddy {
        /// A builder for AVX2 empowered vectors.
        vb: AVX2VectorBuilder,
        /// A list of substrings to match.
        pats: Vec<Vec<u8>>,
        /// An Aho-Corasick automaton of the patterns. We use this when we need to
        /// search pieces smaller than the Teddy block size.
        ac: AhoCorasick,
        /// A set of 8 buckets. Each bucket corresponds to a single member of a
        /// bitset. A bucket contains zero or more substrings. This is useful
        /// when the number of substrings exceeds 8, since our bitsets cannot have
        /// more than 8 members.
        buckets: Vec<Vec<usize>>,
        /// Our set of masks. There's one mask for each byte in the fingerprint.
        masks: Masks,
    }

    impl Teddy {
        /// Returns true if and only if Teddy is supported on this platform.
        ///
        /// If this returns `false`, then `Teddy::new(...)` is guaranteed to
        /// return `None`.
        pub fn available() -> bool {
            AVX2VectorBuilder::new().is_some()
        }

        /// Create a new `Teddy` multi substring matcher.
        ///
        /// If a `Teddy` matcher could not be created (e.g., `pats` is empty or has
        /// an empty substring), then `None` is returned.
        pub fn new(pats: &Literals) -> Option<Teddy> {
            let vb = match AVX2VectorBuilder::new() {
                None => return None,
                Some(vb) => vb,
            };
            if !Teddy::available() {
                return None;
            }

            let pats: Vec<_> = pats.literals().iter().map(|p|p.to_vec()).collect();
            let min_len = pats.iter().map(|p| p.len()).min().unwrap_or(0);
            // Don't allow any empty patterns and require that we have at
            // least one pattern.
            if min_len < 1 {
                return None;
            }
            // Pick the largest mask possible, but no larger than 3.
            let nmasks = cmp::min(3, min_len);
            let mut masks = Masks::new(vb, nmasks);
            let mut buckets = vec![vec![]; 8];
            // Assign a substring to each bucket, and add the bucket's bitfield to
            // the appropriate position in the mask.
            for (pati, pat) in pats.iter().enumerate() {
                let bucket = pati % 8;
                buckets[bucket].push(pati);
                masks.add(bucket as u8, pat);
            }
            let ac = AhoCorasickBuilder::new()
                .match_kind(aho_corasick::MatchKind::LeftmostFirst)
                .dfa(true)
                .prefilter(false)
                .build(&pats);
            Some(Teddy {
                vb: vb,
                pats: pats.to_vec(),
                ac: ac,
                buckets: buckets,
                masks: masks,
            })
        }

        /// Returns all of the substrings matched by this `Teddy`.
        pub fn patterns(&self) -> &[Vec<u8>] {
            &self.pats
        }

        /// Returns the number of substrings in this matcher.
        pub fn len(&self) -> usize {
            self.pats.len()
        }

        /// Returns the approximate size on the heap used by this matcher.
        pub fn approximate_size(&self) -> usize {
            self.pats.iter().fold(0, |a, b| a + b.len())
        }

        /// Searches `haystack` for the substrings in this `Teddy`. If a match was
        /// found, then it is returned. Otherwise, `None` is returned.
        pub fn find(&self, haystack: &[u8]) -> Option<Match> {
            // This is safe because the only way we can construct a Teddy type
            // is if AVX2 is available.
            unsafe { self.find_impl(haystack) }
        }

        #[allow(unused_attributes)]
        #[target_feature(enable = "avx2")]
        unsafe fn find_impl(&self, haystack: &[u8]) -> Option<Match> {
            // If our haystack is smaller than the block size, then fall back to
            // a naive brute force search.
            if haystack.is_empty() || haystack.len() < (BLOCK_SIZE + 2) {
                return self.slow(haystack, 0);
            }
            match self.masks.len() {
                0 => None,
                1 => self.find1(haystack),
                2 => self.find2(haystack),
                3 => self.find3(haystack),
                _ => unreachable!(),
            }
        }

        /// `find1` is used when there is only 1 mask. This is the easy case and is
        /// pretty much as described in the module documentation.
        #[inline(always)]
        fn find1(&self, haystack: &[u8]) -> Option<Match> {
            let mut pos = 0;
            let zero = self.vb.u8x32_splat(0);
            let len = haystack.len();
            debug_assert!(len >= BLOCK_SIZE);
            while pos <= len - BLOCK_SIZE {
                let h = unsafe {
                    // I tried and failed to eliminate bounds checks in safe code.
                    // This is safe because of our loop invariant: pos is always
                    // <= len-32.
                    let p = haystack.get_unchecked(pos..);
                    self.vb.u8x32_load_unchecked_unaligned(p)
                };
                // N.B. `res0` is our `C` in the module documentation.
                let res0 = self.masks.members1(h);
                // Only do expensive verification if there are any non-zero bits.
                let bitfield = res0.ne(zero).movemask();
                if bitfield != 0 {
                    if let Some(m) = self.verify(haystack, pos, res0, bitfield) {
                        return Some(m);
                    }
                }
                pos += BLOCK_SIZE;
            }
            self.slow(haystack, pos)
        }

        /// `find2` is used when there are 2 masks, e.g., the fingerprint is 2 bytes
        /// long.
        #[inline(always)]
        fn find2(&self, haystack: &[u8]) -> Option<Match> {
            // This is an exotic way to right shift a SIMD vector across lanes.
            // See below at use for more details.
            let zero = self.vb.u8x32_splat(0);
            let len = haystack.len();
            // The previous value of `C` (from the module documentation) for the
            // *first* byte in the fingerprint. On subsequent iterations, we take
            // the last bitset from the previous `C` and insert it into the first
            // position of the current `C`, shifting all other bitsets to the right
            // one lane. This causes `C` for the first byte to line up with `C` for
            // the second byte, so that they can be `AND`'d together.
            let mut prev0 = self.vb.u8x32_splat(0xFF);
            let mut pos = 1;
            debug_assert!(len >= BLOCK_SIZE);
            while pos <= len - BLOCK_SIZE {
                let h = unsafe {
                    // I tried and failed to eliminate bounds checks in safe code.
                    // This is safe because of our loop invariant: pos is always
                    // <= len-32.
                    let p = haystack.get_unchecked(pos..);
                    self.vb.u8x32_load_unchecked_unaligned(p)
                };
                let (res0, res1) = self.masks.members2(h);

                // Do this:
                //
                //     (prev0 << 15) | (res0 >> 1)
                //
                // This lets us line up our C values for each byte.
                let res0prev0 = res0.alignr_15(prev0);

                // `AND`'s our `C` values together.
                let res = res0prev0.and(res1);
                prev0 = res0;

                let bitfield = res.ne(zero).movemask();
                if bitfield != 0 {
                    let pos = pos.checked_sub(1).unwrap();
                    if let Some(m) = self.verify(haystack, pos, res, bitfield) {
                        return Some(m);
                    }
                }
                pos += BLOCK_SIZE;
            }
            // The windowing above doesn't check the last byte in the last
            // window, so start the slow search at the last byte of the last
            // window.
            self.slow(haystack, pos.checked_sub(1).unwrap())
        }

        /// `find3` is used when there are 3 masks, e.g., the fingerprint is 3 bytes
        /// long.
        ///
        /// N.B. This is a straight-forward extrapolation of `find2`. The only
        /// difference is that we need to keep track of two previous values of `C`,
        /// since we now need to align for three bytes.
        #[inline(always)]
        fn find3(&self, haystack: &[u8]) -> Option<Match> {
            let zero = self.vb.u8x32_splat(0);
            let len = haystack.len();
            let mut prev0 = self.vb.u8x32_splat(0xFF);
            let mut prev1 = self.vb.u8x32_splat(0xFF);
            let mut pos = 2;

            while pos <= len - BLOCK_SIZE {
                let h = unsafe {
                    // I tried and failed to eliminate bounds checks in safe code.
                    // This is safe because of our loop invariant: pos is always
                    // <= len-32.
                    let p = haystack.get_unchecked(pos..);
                    self.vb.u8x32_load_unchecked_unaligned(p)
                };
                let (res0, res1, res2) = self.masks.members3(h);

                let res0prev0 = res0.alignr_14(prev0);
                let res1prev1 = res1.alignr_15(prev1);
                let res = res0prev0.and(res1prev1).and(res2);

                prev0 = res0;
                prev1 = res1;

                let bitfield = res.ne(zero).movemask();
                if bitfield != 0 {
                    let pos = pos.checked_sub(2).unwrap();
                    if let Some(m) = self.verify(haystack, pos, res, bitfield) {
                        return Some(m);
                    }
                }
                pos += BLOCK_SIZE;
            }
            // The windowing above doesn't check the last two bytes in the last
            // window, so start the slow search at the penultimate byte of the
            // last window.
            // self.slow(haystack, pos.saturating_sub(2))
            self.slow(haystack, pos.checked_sub(2).unwrap())
        }

        /// Runs the verification procedure on `res` (i.e., `C` from the module
        /// documentation), where the haystack block starts at `pos` in
        /// `haystack`. `bitfield` has ones in the bit positions that `res` has
        /// non-zero bytes.
        ///
        /// If a match exists, it returns the first one.
        #[inline(always)]
        fn verify(
            &self,
            haystack: &[u8],
            pos: usize,
            res: u8x32,
            mut bitfield: u32,
        ) -> Option<Match> {
            let patterns = res.bytes();
            while bitfield != 0 {
                // The next offset, relative to pos, where some fingerprint
                // matched.
                let byte_pos = bitfield.trailing_zeros() as usize;
                bitfield &= !(1 << byte_pos);

                // Offset relative to the beginning of the haystack.
                let start = pos + byte_pos;

                // The bitfield telling us which patterns had fingerprints that
                // match at this starting position.
                let mut patterns = patterns[byte_pos];
                while patterns != 0 {
                    let bucket = patterns.trailing_zeros() as usize;
                    patterns &= !(1 << bucket);

                    // Actual substring search verification.
                    if let Some(m) = self.verify_bucket(haystack, bucket, start) {
                        return Some(m);
                    }
                }
            }

            None
        }

        /// Verifies whether any substring in the given bucket matches in haystack
        /// at the given starting position.
        #[inline(always)]
        fn verify_bucket(
            &self,
            haystack: &[u8],
            bucket: usize,
            start: usize,
        ) -> Option<Match> {
            // This cycles through the patterns in the bucket in the order that
            // the patterns were given. Therefore, we guarantee leftmost-first
            // semantics.
            for &pati in &self.buckets[bucket] {
                let pat = &*self.pats[pati];
                if start + pat.len() > haystack.len() {
                    continue;
                }
                if pat == &haystack[start..start + pat.len()] {
                    return Some(Match {
                        pat: pati,
                        start: start,
                        end: start + pat.len(),
                    });
                }
            }
            None
        }

        /// Slow substring search through all patterns in this matcher.
        ///
        /// This is used when we don't have enough bytes in the haystack for our
        /// block based approach.
        #[inline(never)]
        fn slow(&self, haystack: &[u8], pos: usize) -> Option<Match> {
            self.ac.find(&haystack[pos..]).map(|m| {
                Match {
                    pat: m.pattern(),
                    start: pos + m.start(),
                    end: pos + m.end(),
                }
            })
        }
    }

    /// A list of masks. This has length equal to the length of the fingerprint.
    /// The length of the fingerprint is always `min(3, len(smallest_substring))`.
    #[derive(Debug, Clone)]
    struct Masks {
        vb: AVX2VectorBuilder,
        masks: [Mask; 3],
        size: usize,
    }

    impl Masks {
        /// Create a new set of masks of size `n`, where `n` corresponds to the
        /// number of bytes in a fingerprint.
        fn new(vb: AVX2VectorBuilder, n: usize) -> Masks {
            Masks {
                vb: vb,
                masks: [Mask::new(vb), Mask::new(vb), Mask::new(vb)],
                size: n,
            }
        }

        /// Returns the number of masks.
        fn len(&self) -> usize {
            self.size
        }

        /// Adds the given pattern to the given bucket. The bucket should be a
        /// power of `2 <= 2^7`.
        fn add(&mut self, bucket: u8, pat: &[u8]) {
            for i in 0..self.len() {
                self.masks[i].add(bucket, pat[i]);
            }
        }

        /// Finds the fingerprints that are in the given haystack block. i.e., this
        /// returns `C` as described in the module documentation.
        ///
        /// More specifically, `for i in 0..16` and `j in 0..8, C[i][j] == 1` if and
        /// only if `haystack_block[i]` corresponds to a fingerprint that is part
        /// of a pattern in bucket `j`.
        #[inline(always)]
        fn members1(&self, haystack_block: u8x32) -> u8x32 {
            let masklo = self.vb.u8x32_splat(0xF);
            let hlo = haystack_block.and(masklo);
            let hhi = haystack_block.bit_shift_right_4().and(masklo);

            self.masks[0].lo.shuffle(hlo).and(self.masks[0].hi.shuffle(hhi))
        }

        /// Like members1, but computes C for the first and second bytes in the
        /// fingerprint.
        #[inline(always)]
        fn members2(&self, haystack_block: u8x32) -> (u8x32, u8x32) {
            let masklo = self.vb.u8x32_splat(0xF);
            let hlo = haystack_block.and(masklo);
            let hhi = haystack_block.bit_shift_right_4().and(masklo);

            let res0 =
                self.masks[0].lo.shuffle(hlo).and(self.masks[0].hi.shuffle(hhi));
            let res1 =
                self.masks[1].lo.shuffle(hlo).and(self.masks[1].hi.shuffle(hhi));
            (res0, res1)
        }

        /// Like `members1`, but computes `C` for the first, second and third bytes
        /// in the fingerprint.
        #[inline(always)]
        fn members3(&self, haystack_block: u8x32) -> (u8x32, u8x32, u8x32) {
            let masklo = self.vb.u8x32_splat(0xF);
            let hlo = haystack_block.and(masklo);
            let hhi = haystack_block.bit_shift_right_4().and(masklo);

            let res0 =
                self.masks[0].lo.shuffle(hlo).and(self.masks[0].hi.shuffle(hhi));
            let res1 =
                self.masks[1].lo.shuffle(hlo).and(self.masks[1].hi.shuffle(hhi));
            let res2 =
                self.masks[2].lo.shuffle(hlo).and(self.masks[2].hi.shuffle(hhi));
            (res0, res1, res2)
        }
    }

    /// A single mask.
    #[derive(Debug, Clone, Copy)]
    struct Mask {
        /// Bitsets for the low nybbles in a fingerprint.
        lo: u8x32,
        /// Bitsets for the high nybbles in a fingerprint.
        hi: u8x32,
    }

    impl Mask {
        /// Create a new mask with no members.
        fn new(vb: AVX2VectorBuilder) -> Mask {
            Mask {
                lo: vb.u8x32_splat(0),
                hi: vb.u8x32_splat(0),
            }
        }

        /// Adds the given byte to the given bucket.
        fn add(&mut self, bucket: u8, byte: u8) {
            // Split our byte into two nybbles, and add each nybble to our
            // mask.
            let byte_lo = (byte & 0xF) as usize;
            let byte_hi = (byte >> 4) as usize;

            {
                let mut lo_bytes = self.lo.bytes();
                let lo = lo_bytes[byte_lo] | ((1 << bucket) as u8);
                lo_bytes[byte_lo] = lo;
                lo_bytes[byte_lo + 16] = lo;
                self.lo.replace_bytes(lo_bytes);
            }

            {
                let mut hi_bytes = self.hi.bytes();
                let hi = hi_bytes[byte_hi] | ((1 << bucket) as u8);
                hi_bytes[byte_hi] = hi;
                hi_bytes[byte_hi + 16] = hi;
                self.hi.replace_bytes(hi_bytes);
            }
        }
    }

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