ARM Architecture Reference Manual ARMv7-A and ARMv7-R edition

Instruction Details
A8.6.406 VTBL, VTBX
Vector Table Lookup uses byte indexes in a control vector to look up byte values in a table and generate a
new vector. Indexes out of range return 0.
Vector Table Extension works in the same way, except that indexes out of range leave the destination
element unchanged.
Encoding T1 / A1 Advanced SIMD
V.8 , ,
15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
1 1 1 1 1 1 1 1 1 D 1 1 Vn Vd 1 0 len N op M 0 Vm
31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
1 1 1 1 0 0 1 1 1 D 1 1 Vn Vd 1 0 len N op M 0 Vm
is_vtbl = (op == ‘0’); length = UInt(len)+1;
d = UInt(D:Vd); n = UInt(N:Vn); m = UInt(M:Vm);
if n+length > 32 then UNPREDICTABLE;
A8-798 Copyright © 1996-1998, 2000, 2004-2008 ARM Limited. All rights reserved. ARM DDI 0406B