diff --git a/vendor/github.com/cespare/xxhash/xxhash_amd64.s b/vendor/github.com/cespare/xxhash/xxhash_amd64.s
new file mode 100644
index 0000000..757f201
--- /dev/null
+++ b/vendor/github.com/cespare/xxhash/xxhash_amd64.s
@@ -0,0 +1,233 @@
+// +build !appengine
+// +build gc
+// +build !purego
+
+#include "textflag.h"
+
+// Register allocation:
+// AX	h
+// CX	pointer to advance through b
+// DX	n
+// BX	loop end
+// R8	v1, k1
+// R9	v2
+// R10	v3
+// R11	v4
+// R12	tmp
+// R13	prime1v
+// R14	prime2v
+// R15	prime4v
+
+// round reads from and advances the buffer pointer in CX.
+// It assumes that R13 has prime1v and R14 has prime2v.
+#define round(r) \
+	MOVQ  (CX), R12 \
+	ADDQ  $8, CX    \
+	IMULQ R14, R12  \
+	ADDQ  R12, r    \
+	ROLQ  $31, r    \
+	IMULQ R13, r
+
+// mergeRound applies a merge round on the two registers acc and val.
+// It assumes that R13 has prime1v, R14 has prime2v, and R15 has prime4v.
+#define mergeRound(acc, val) \
+	IMULQ R14, val \
+	ROLQ  $31, val \
+	IMULQ R13, val \
+	XORQ  val, acc \
+	IMULQ R13, acc \
+	ADDQ  R15, acc
+
+// func Sum64(b []byte) uint64
+TEXT ·Sum64(SB), NOSPLIT, $0-32
+	// Load fixed primes.
+	MOVQ ·prime1v(SB), R13
+	MOVQ ·prime2v(SB), R14
+	MOVQ ·prime4v(SB), R15
+
+	// Load slice.
+	MOVQ b_base+0(FP), CX
+	MOVQ b_len+8(FP), DX
+	LEAQ (CX)(DX*1), BX
+
+	// The first loop limit will be len(b)-32.
+	SUBQ $32, BX
+
+	// Check whether we have at least one block.
+	CMPQ DX, $32
+	JLT  noBlocks
+
+	// Set up initial state (v1, v2, v3, v4).
+	MOVQ R13, R8
+	ADDQ R14, R8
+	MOVQ R14, R9
+	XORQ R10, R10
+	XORQ R11, R11
+	SUBQ R13, R11
+
+	// Loop until CX > BX.
+blockLoop:
+	round(R8)
+	round(R9)
+	round(R10)
+	round(R11)
+
+	CMPQ CX, BX
+	JLE  blockLoop
+
+	MOVQ R8, AX
+	ROLQ $1, AX
+	MOVQ R9, R12
+	ROLQ $7, R12
+	ADDQ R12, AX
+	MOVQ R10, R12
+	ROLQ $12, R12
+	ADDQ R12, AX
+	MOVQ R11, R12
+	ROLQ $18, R12
+	ADDQ R12, AX
+
+	mergeRound(AX, R8)
+	mergeRound(AX, R9)
+	mergeRound(AX, R10)
+	mergeRound(AX, R11)
+
+	JMP afterBlocks
+
+noBlocks:
+	MOVQ ·prime5v(SB), AX
+
+afterBlocks:
+	ADDQ DX, AX
+
+	// Right now BX has len(b)-32, and we want to loop until CX > len(b)-8.
+	ADDQ $24, BX
+
+	CMPQ CX, BX
+	JG   fourByte
+
+wordLoop:
+	// Calculate k1.
+	MOVQ  (CX), R8
+	ADDQ  $8, CX
+	IMULQ R14, R8
+	ROLQ  $31, R8
+	IMULQ R13, R8
+
+	XORQ  R8, AX
+	ROLQ  $27, AX
+	IMULQ R13, AX
+	ADDQ  R15, AX
+
+	CMPQ CX, BX
+	JLE  wordLoop
+
+fourByte:
+	ADDQ $4, BX
+	CMPQ CX, BX
+	JG   singles
+
+	MOVL  (CX), R8
+	ADDQ  $4, CX
+	IMULQ R13, R8
+	XORQ  R8, AX
+
+	ROLQ  $23, AX
+	IMULQ R14, AX
+	ADDQ  ·prime3v(SB), AX
+
+singles:
+	ADDQ $4, BX
+	CMPQ CX, BX
+	JGE  finalize
+
+singlesLoop:
+	MOVBQZX (CX), R12
+	ADDQ    $1, CX
+	IMULQ   ·prime5v(SB), R12
+	XORQ    R12, AX
+
+	ROLQ  $11, AX
+	IMULQ R13, AX
+
+	CMPQ CX, BX
+	JL   singlesLoop
+
+finalize:
+	MOVQ  AX, R12
+	SHRQ  $33, R12
+	XORQ  R12, AX
+	IMULQ R14, AX
+	MOVQ  AX, R12
+	SHRQ  $29, R12
+	XORQ  R12, AX
+	IMULQ ·prime3v(SB), AX
+	MOVQ  AX, R12
+	SHRQ  $32, R12
+	XORQ  R12, AX
+
+	MOVQ AX, ret+24(FP)
+	RET
+
+// writeBlocks uses the same registers as above except that it uses AX to store
+// the x pointer.
+
+// func writeBlocks(x *xxh, b []byte) []byte
+TEXT ·writeBlocks(SB), NOSPLIT, $0-56
+	// Load fixed primes needed for round.
+	MOVQ ·prime1v(SB), R13
+	MOVQ ·prime2v(SB), R14
+
+	// Load slice.
+	MOVQ b_base+8(FP), CX
+	MOVQ CX, ret_base+32(FP) // initialize return base pointer; see NOTE below
+	MOVQ b_len+16(FP), DX
+	LEAQ (CX)(DX*1), BX
+	SUBQ $32, BX
+
+	// Load vN from x.
+	MOVQ x+0(FP), AX
+	MOVQ 0(AX), R8   // v1
+	MOVQ 8(AX), R9   // v2
+	MOVQ 16(AX), R10 // v3
+	MOVQ 24(AX), R11 // v4
+
+	// We don't need to check the loop condition here; this function is
+	// always called with at least one block of data to process.
+blockLoop:
+	round(R8)
+	round(R9)
+	round(R10)
+	round(R11)
+
+	CMPQ CX, BX
+	JLE  blockLoop
+
+	// Copy vN back to x.
+	MOVQ R8, 0(AX)
+	MOVQ R9, 8(AX)
+	MOVQ R10, 16(AX)
+	MOVQ R11, 24(AX)
+
+	// Construct return slice.
+	// NOTE: It's important that we don't construct a slice that has a base
+	// pointer off the end of the original slice, as in Go 1.7+ this will
+	// cause runtime crashes. (See discussion in, for example,
+	// https://github.com/golang/go/issues/16772.)
+	// Therefore, we calculate the length/cap first, and if they're zero, we
+	// keep the old base. This is what the compiler does as well if you
+	// write code like
+	//   b = b[len(b):]
+
+	// New length is 32 - (CX - BX) -> BX+32 - CX.
+	ADDQ $32, BX
+	SUBQ CX, BX
+	JZ   afterSetBase
+
+	MOVQ CX, ret_base+32(FP)
+
+afterSetBase:
+	MOVQ BX, ret_len+40(FP)
+	MOVQ BX, ret_cap+48(FP) // set cap == len
+
+	RET