+/*
+ * If (0 <= index <= 15), then call the ASIMD ext instruction on the
+ * 128 bit regs v0 and v1 with the appropriate index.
+ *
+ * Else returns a zero vector.
+ */
+static inline uint8x16_t
+vextract(uint8x16_t v0, uint8x16_t v1, const int index)
+{
+ switch (index) {
+ case 0: return vextq_u8(v0, v1, 0);
+ case 1: return vextq_u8(v0, v1, 1);
+ case 2: return vextq_u8(v0, v1, 2);
+ case 3: return vextq_u8(v0, v1, 3);
+ case 4: return vextq_u8(v0, v1, 4);
+ case 5: return vextq_u8(v0, v1, 5);
+ case 6: return vextq_u8(v0, v1, 6);
+ case 7: return vextq_u8(v0, v1, 7);
+ case 8: return vextq_u8(v0, v1, 8);
+ case 9: return vextq_u8(v0, v1, 9);
+ case 10: return vextq_u8(v0, v1, 10);
+ case 11: return vextq_u8(v0, v1, 11);
+ case 12: return vextq_u8(v0, v1, 12);
+ case 13: return vextq_u8(v0, v1, 13);
+ case 14: return vextq_u8(v0, v1, 14);
+ case 15: return vextq_u8(v0, v1, 15);
+ }
+ return vdupq_n_u8(0);
+}
+
+/**
+ * Shifts right 128 bit register by specified number of bytes
+ *
+ * Value of shift parameter must be in range 0 - 16
+ */
+static inline uint64x2_t
+vshift_bytes_right(uint64x2_t reg, const unsigned int shift)
+{
+ return vreinterpretq_u64_u8(vextract(
+ vreinterpretq_u8_u64(reg),
+ vdupq_n_u8(0),
+ shift));
+}
+
+/**
+ * Shifts left 128 bit register by specified number of bytes
+ *
+ * Value of shift parameter must be in range 0 - 16
+ */
+static inline uint64x2_t
+vshift_bytes_left(uint64x2_t reg, const unsigned int shift)
+{
+ return vreinterpretq_u64_u8(vextract(
+ vdupq_n_u8(0),
+ vreinterpretq_u8_u64(reg),
+ 16 - shift));
+}
+