cls

Count Leading Sign Bits

CLS <Wd>, <Wn>

Counts number of consecutive sign bits.

Pseudocode Operation

count ← 0
msb ← Wn[31]
for i = 30 downto 0
  if Wn[i] == msb then
    count ← count + 1
  else
    break
Wd ← count

Example

CLS w0, w1

Encoding

Binary Layout

11010110

28:21

00000

20:16

00010

15:11

9:5

4:0

Format Data Processing

Opcode 0x5AC01400

Extension Base

Operands

Wd
Destination 32-bit integer register
Wn
First source / base 32-bit integer register

Reference

View in Arm A64 ISA Reference ↗ Arm A64 ISA

Instruction Forms

Encoding	Instruction	ISA	Bit pattern
0x0E204800	CLS <Vd>.<T>, <Vn>.<T>	A64	0 \| Q \| 0 \| 01110 \| size \| 10000 \| 00100 \| 10 \| Rn \| Rd
0x5AC01400	CLS <Wd>, <Wn>	A64	0 \| 1 \| 0 \| 11010110 \| 00000 \| 00010 \| 1 \| Rn \| Rd
0xDAC01400	CLS <Xd>, <Xn>	A64	1 \| 1 \| 0 \| 11010110 \| 00000 \| 00010 \| 1 \| Rn \| Rd
0x0418A000	CLS <Zd>.<T>, <Pg>/M, <Zn>.<T>	A64	00000100 \| size \| 011 \| 00 \| 0 \| 101 \| Pg \| Zn \| Zd

Description

Count Leading Sign bits counts the number of leading bits of the source register that have the same value as the most significant bit of the register, and writes the result to the destination register. This count does not include the most significant bit of the source register.

Operation

integer result;
bits(datasize) operand1 = X[n, datasize];

result = CountLeadingSignBits(operand1);

X[d, datasize] = result<datasize-1:0>;

cls