CLZ -- A64

This instruction counts the number of consecutive binary zero bits, starting from the most significant bit in the source register, and places the count in the destination register.

Decode for all variants of this encoding

constant integer d = UInt(Rd); constant integer n = UInt(Rn); constant integer datasize = 32 << UInt(sf);

Assembler Symbols

<Wd>	Is the 32-bit name of the general-purpose destination register, encoded in the "Rd" field.

<Wn>	Is the 32-bit name of the general-purpose source register, encoded in the "Rn" field.

<Xd>	Is the 64-bit name of the general-purpose destination register, encoded in the "Rd" field.

<Xn>	Is the 64-bit name of the general-purpose source register, encoded in the "Rn" field.

Operation

constant bits(datasize) operand1 = X[n, datasize]; constant integer result = CountLeadingZeroBits(operand1); X[d, datasize] = result<datasize-1:0>;

Operational information

If PSTATE.DIT is 1:

The execution time of this instruction is independent of:
- The values of the data supplied in any of its registers.
- The values of the NZCV flags.
The response of this instruction to asynchronous exceptions does not vary based on:
- The values of the data supplied in any of its registers.
- The values of the NZCV flags.

Internal version only: aarchmrs v2025-03_rel, pseudocode v2025-03_rel ; Build timestamp: 2025-03-21T17:41

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
sf	1	0	1	1	0	1	0	1	1	0	0	0	0	0	0	0	0	0	1	0	0	Rn					Rd
		S									opcode2										op

CLZ

Encoding for the 32-bit variant

Encoding for the 64-bit variant

Decode for all variants of this encoding

Assembler Symbols

Operation

Operational information