Modern Assembly Language Programming with the ARM Processor

10.9.8 Count Bits

These instructions can be used to count leading sign bits or zeros, or to count the number of bits that are set for each element in a vector:

vcls Count Leading Sign Bits

vclz Count Leading Zero Bits

vcnt Count Set Bits

Syntax

 v<op>.<type> Vd, Vm

• <op> is either cls, clz or cnt.

• The valid choices for <type> are given in the following table:

Opcode	Valid Types
vcls	s8, s16, or s32
vclz	u8, u16, or u32
vcnt	i8

Operations

Name	Effect	Description
vcls	$n\leftarrow \text{\# of elements}$ for 0 ≤ i < n) do  $Vd[i]\leftarrow leadin\mathrm{g\_}sig\mathrm{n\_}bits(Vm[i])$ end for	Count the number ...