cnttzdm

Count Trailing Zeros Doubleword under Mask

cnttzdm RA, RS, RB

Counts trailing zeros in RS, but only considering bits set in mask RB.

Encoding

Binary Layout

31

0:5

RS

6:10

RA

11:15

RB

16:20

571

21:30

/

31

 

Format X-form

Opcode 0x7C000476

Extension Base

Operands

• RA
  Target
• RS
  Source
• RB
  Mask
• RT
  Target General Purpose Register

Example

cnttzdm r4, r3, r5

Registers Altered

CR0, XER

Related

More in Base

Reference

View in PowerISA v3.1C Specification ↗ OPF Power ISA v3.1C

Description

Counts the number of trailing zeros in RS considering only the bit positions set to 1 in the mask RB (Power10 Scalar). The count is placed in RA. No CR, XER, or FPSCR fields are affected.

Operation

mask ← RB; masked_value ← RS ∧ mask; if (masked_value = 0) then RA ← 64; else count ← 0; for i in 63 downto 0 do; if (masked_value[i] = 1) then break; count ← count + 1; RA ← count;

Programming Note

The cnttzdm instruction is useful for counting trailing zeros in a doubleword while applying a mask. Ensure that the mask register (RB) has bits set to 1 where you want to consider the corresponding bits in the source register (RS). The result is zero-extended to 64 bits before being stored in the destination register (RA). This instruction operates at user privilege level and does not generate any exceptions under normal conditions. Performance may vary based on the distribution of zeros and ones in the registers.