diff --git a/vendor/github.com/cespare/xxhash/xxhash.go b/vendor/github.com/cespare/xxhash/xxhash.go
new file mode 100644
index 0000000..f896bd2
--- /dev/null
+++ b/vendor/github.com/cespare/xxhash/xxhash.go
@@ -0,0 +1,168 @@
+// Package xxhash implements the 64-bit variant of xxHash (XXH64) as described
+// at http://cyan4973.github.io/xxHash/.
+package xxhash
+
+import (
+	"encoding/binary"
+	"hash"
+)
+
+const (
+	prime1 uint64 = 11400714785074694791
+	prime2 uint64 = 14029467366897019727
+	prime3 uint64 = 1609587929392839161
+	prime4 uint64 = 9650029242287828579
+	prime5 uint64 = 2870177450012600261
+)
+
+// NOTE(caleb): I'm using both consts and vars of the primes. Using consts where
+// possible in the Go code is worth a small (but measurable) performance boost
+// by avoiding some MOVQs. Vars are needed for the asm and also are useful for
+// convenience in the Go code in a few places where we need to intentionally
+// avoid constant arithmetic (e.g., v1 := prime1 + prime2 fails because the
+// result overflows a uint64).
+var (
+	prime1v = prime1
+	prime2v = prime2
+	prime3v = prime3
+	prime4v = prime4
+	prime5v = prime5
+)
+
+type xxh struct {
+	v1    uint64
+	v2    uint64
+	v3    uint64
+	v4    uint64
+	total int
+	mem   [32]byte
+	n     int // how much of mem is used
+}
+
+// New creates a new hash.Hash64 that implements the 64-bit xxHash algorithm.
+func New() hash.Hash64 {
+	var x xxh
+	x.Reset()
+	return &x
+}
+
+func (x *xxh) Reset() {
+	x.n = 0
+	x.total = 0
+	x.v1 = prime1v + prime2
+	x.v2 = prime2
+	x.v3 = 0
+	x.v4 = -prime1v
+}
+
+func (x *xxh) Size() int      { return 8 }
+func (x *xxh) BlockSize() int { return 32 }
+
+// Write adds more data to x. It always returns len(b), nil.
+func (x *xxh) Write(b []byte) (n int, err error) {
+	n = len(b)
+	x.total += len(b)
+
+	if x.n+len(b) < 32 {
+		// This new data doesn't even fill the current block.
+		copy(x.mem[x.n:], b)
+		x.n += len(b)
+		return
+	}
+
+	if x.n > 0 {
+		// Finish off the partial block.
+		copy(x.mem[x.n:], b)
+		x.v1 = round(x.v1, u64(x.mem[0:8]))
+		x.v2 = round(x.v2, u64(x.mem[8:16]))
+		x.v3 = round(x.v3, u64(x.mem[16:24]))
+		x.v4 = round(x.v4, u64(x.mem[24:32]))
+		b = b[32-x.n:]
+		x.n = 0
+	}
+
+	if len(b) >= 32 {
+		// One or more full blocks left.
+		b = writeBlocks(x, b)
+	}
+
+	// Store any remaining partial block.
+	copy(x.mem[:], b)
+	x.n = len(b)
+
+	return
+}
+
+func (x *xxh) Sum(b []byte) []byte {
+	s := x.Sum64()
+	return append(
+		b,
+		byte(s>>56),
+		byte(s>>48),
+		byte(s>>40),
+		byte(s>>32),
+		byte(s>>24),
+		byte(s>>16),
+		byte(s>>8),
+		byte(s),
+	)
+}
+
+func (x *xxh) Sum64() uint64 {
+	var h uint64
+
+	if x.total >= 32 {
+		v1, v2, v3, v4 := x.v1, x.v2, x.v3, x.v4
+		h = rol1(v1) + rol7(v2) + rol12(v3) + rol18(v4)
+		h = mergeRound(h, v1)
+		h = mergeRound(h, v2)
+		h = mergeRound(h, v3)
+		h = mergeRound(h, v4)
+	} else {
+		h = x.v3 + prime5
+	}
+
+	h += uint64(x.total)
+
+	i, end := 0, x.n
+	for ; i+8 <= end; i += 8 {
+		k1 := round(0, u64(x.mem[i:i+8]))
+		h ^= k1
+		h = rol27(h)*prime1 + prime4
+	}
+	if i+4 <= end {
+		h ^= uint64(u32(x.mem[i:i+4])) * prime1
+		h = rol23(h)*prime2 + prime3
+		i += 4
+	}
+	for i < end {
+		h ^= uint64(x.mem[i]) * prime5
+		h = rol11(h) * prime1
+		i++
+	}
+
+	h ^= h >> 33
+	h *= prime2
+	h ^= h >> 29
+	h *= prime3
+	h ^= h >> 32
+
+	return h
+}
+
+func u64(b []byte) uint64 { return binary.LittleEndian.Uint64(b) }
+func u32(b []byte) uint32 { return binary.LittleEndian.Uint32(b) }
+
+func round(acc, input uint64) uint64 {
+	acc += input * prime2
+	acc = rol31(acc)
+	acc *= prime1
+	return acc
+}
+
+func mergeRound(acc, val uint64) uint64 {
+	val = round(0, val)
+	acc ^= val
+	acc = acc*prime1 + prime4
+	return acc
+}