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ARM Compiler armasm User Guide : VTBL and VTBX

VTBL and VTBX

Vector Table Lookup, Vector Table Extension.

Syntax

Vop{cond}.8 Dd, list, Dm

where:

op

must be either TBL or TBX.

cond

is an optional condition code.

Dd

specifies the destination vector.

list

Specifies the vectors containing the table. It must be one of:

  • {Dn}.

  • {Dn,D(n+1)}.

  • {Dn,D(n+1),D(n+2)}.

  • {Dn,D(n+1),D(n+2),D(n+3)}.

  • {Qn,Q(n+1)}.

All the registers in list must be in the range D0-D31 or Q0-Q15 and must not wrap around the end of the register bank. For example {D31,D0,D1} is not permitted. If list contains Q registers, they disassemble to the equivalent D registers.

Dm

specifies the index vector.

Operation

VTBL 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 zero.

VTBX works in the same way, except that indexes out of range leave the destination element unchanged.

Related reference

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