diff --git a/tz/avx.go b/tz/avx.go
index 4a61702..4b025b2 100644
--- a/tz/avx.go
+++ b/tz/avx.go
@@ -57,14 +57,15 @@ func (d *digest) Reset() {
 func (d *digest) Write(data []byte) (n int, err error) {
 	n = len(data)
 	for _, b := range data {
-		mulBitRight(&d.x[0], &d.x[1], &d.x[2], &d.x[3], &minmax[(b>>7)&1])
-		mulBitRight(&d.x[0], &d.x[1], &d.x[2], &d.x[3], &minmax[(b>>6)&1])
-		mulBitRight(&d.x[0], &d.x[1], &d.x[2], &d.x[3], &minmax[(b>>5)&1])
-		mulBitRight(&d.x[0], &d.x[1], &d.x[2], &d.x[3], &minmax[(b>>4)&1])
-		mulBitRight(&d.x[0], &d.x[1], &d.x[2], &d.x[3], &minmax[(b>>3)&1])
-		mulBitRight(&d.x[0], &d.x[1], &d.x[2], &d.x[3], &minmax[(b>>2)&1])
-		mulBitRight(&d.x[0], &d.x[1], &d.x[2], &d.x[3], &minmax[(b>>1)&1])
-		mulBitRight(&d.x[0], &d.x[1], &d.x[2], &d.x[3], &minmax[(b>>0)&1])
+		mulByteRight(&d.x[0], &d.x[1], &d.x[2], &d.x[3], b)
+		// mulBitRight(&d.x[0], &d.x[1], &d.x[2], &d.x[3], &minmax[(b>>7)&1])
+		// mulBitRight(&d.x[0], &d.x[1], &d.x[2], &d.x[3], &minmax[(b>>6)&1])
+		// mulBitRight(&d.x[0], &d.x[1], &d.x[2], &d.x[3], &minmax[(b>>5)&1])
+		// mulBitRight(&d.x[0], &d.x[1], &d.x[2], &d.x[3], &minmax[(b>>4)&1])
+		// mulBitRight(&d.x[0], &d.x[1], &d.x[2], &d.x[3], &minmax[(b>>3)&1])
+		// mulBitRight(&d.x[0], &d.x[1], &d.x[2], &d.x[3], &minmax[(b>>2)&1])
+		// mulBitRight(&d.x[0], &d.x[1], &d.x[2], &d.x[3], &minmax[(b>>1)&1])
+		// mulBitRight(&d.x[0], &d.x[1], &d.x[2], &d.x[3], &minmax[(b>>0)&1])
 	}
 	return
 }
@@ -78,3 +79,5 @@ func (d *digest) BlockSize() int {
 }
 
 func mulBitRight(c00, c01, c10, c11, e *gf127.GF127)
+
+func mulByteRight(c00, c01, c10, c11 *gf127.GF127, b byte)
diff --git a/tz/avx_amd64.s b/tz/avx_amd64.s
index 97e41b9..deb8ec1 100644
--- a/tz/avx_amd64.s
+++ b/tz/avx_amd64.s
@@ -12,6 +12,62 @@
     XORPD R2, TO \
     XORPD R3, TO
 
+
+#define mask(bit, src, tmp, to1, to2) \
+    MOVQ src, tmp \
+    SHRQ bit, tmp \
+    ANDQ $1, tmp  \
+    NEGQ tmp      \
+    MOVQ tmp, to1 \
+    VPBROADCASTB to1, to2
+    // FIXME VPBROADCASTB is AVX2 instruction
+    //https://software.intel.com/en-us/forums/intel-isa-extensions/topic/301461
+
+#define mulBit(bit) \
+    MOVUPD X0, X8 \
+    MOVUPD X2, X9 \
+    mul2(X0, X5, X6, X7) \
+    VXORPD X1, X5, X0 \
+    mul2(X2, X5, X6, X7) \
+    VXORPD X3, X5, X2 \
+    mask(bit, CX, DX, X6, X5) \
+    VANDPD X0, X5, X1 \
+    XORPD X8, X1 \
+    VANDPD X2, X5, X3 \
+    XORPD X9, X3
+
+
+// func mulBitRight(c00, c01, c10, c11 *[2]uint64, byte)
+TEXT ·mulByteRight(SB),NOSPLIT,$0
+    MOVQ c00+0(FP), AX
+    MOVUPD (AX), X0
+    MOVQ c01+8(FP), BX
+    MOVUPD (BX), X1
+    MOVQ c10+16(FP), CX
+    MOVUPD (CX), X2
+    MOVQ c11+24(FP), DX
+    MOVUPD (DX), X3
+    MOVB e+32(FP), CX
+
+    mulBit($7)
+    mulBit($6)
+    mulBit($5)
+    mulBit($4)
+    mulBit($3)
+    mulBit($2)
+    mulBit($1)
+    mulBit($0)
+
+    MOVUPD X0, (AX)
+    MOVQ c10+16(FP), CX
+    MOVUPD X2, (CX)
+    MOVUPD X1, (BX)
+    MOVQ c11+24(FP), DX
+    MOVUPD X3, (DX)
+
+    RET
+
+
 // func mulBitRight(c00, c01, c10, c11, e *[2]uint64)
 TEXT ·mulBitRight(SB),NOSPLIT,$0
     MOVQ c00+0(FP), AX
@@ -25,40 +81,24 @@ TEXT ·mulBitRight(SB),NOSPLIT,$0
     MOVQ c11+24(FP), DX
     MOVUPD (DX), X3
 
-    // c00 *= 2
     mul2(X0, X5, X6, X7)
-    MOVUPD X5, X0
-
-    // c00 += c01
-    XORPD X1, X0
-    MOVUPD X0, (AX)
-
-    // c10 *= 2
+    VXORPD X1, X5, X0
     mul2(X2, X5, X6, X7)
-    MOVUPD X5, X2
-
-    // c10 += c11
-    XORPD X3, X2
-    MOVUPD X2, (CX)
-
-    MOVQ e+32(FP), AX
-    MOVUPD (AX), X5
-
-    // c01 = c00 + e
+    VXORPD X3, X5, X2
+    MOVQ e+32(FP), CX
+    MOVUPD (CX), X5
     VANDPD X0, X5, X1
-
-    // c01 += X8 (old c00)
     XORPD X8, X1
-    MOVUPD X1, (BX)
-
-    // c11 = c10 + e
     VANDPD X2, X5, X3
-
-    // c11 += X9 (old c10)
     XORPD X9, X3
-    MOVUPD X3, (DX)
-    RET
 
+    MOVUPD X0, (AX)
+    MOVQ c10+16(FP), CX
+    MOVUPD X2, (CX)
+    MOVUPD X1, (BX)
+    MOVUPD X3, (DX)
+
+    RET
 
 // func mulBitRightx2(c00c10, c01c11 *[4]uint64, e *[2]uint64)
 TEXT ·mulBitRightx2(SB),NOSPLIT,$0