Assembler Language Reference

cntlzw or cntlz (Count Leading Zeros Word) Instruction

Purpose

Places the number of leading zeros from a source general-purpose register in a general-purpose register.

Syntax

Bits	Value
0-5	31
6-10	RS
11-15	RA
16-20	///
21-30	26
31	Rc

PowerPC
cntlzw	RA, RS
cntlzw.	RA, RS

POWER family
cntlz	RA, RS
cntlz.	RA, RS

Description

The cntlzw and cntlz instructions count the number (between 0 and 32 inclusive) of consecutive zero bits starting at bit 0 of general-purpose register (GPR) RS and store the result in the target GPR RA.

Syntax Form	Overflow Exception (OE)	Fixed-Point Exception Register	Record Bit (Rc)	Condition Register Field 0
cntlzw	None	None	0	None
cntlzw.	None	None	1	LT,GT,EQ,SO
cntlz	None	None	0	None
cntlz.	None	None	1	LT,GT,EQ,SO

The two syntax forms of the cntlzw instruction and the two syntax forms of the cntlz instruction never affect the Fixed-Point Exception Register. If the syntax form sets the Record (Rc) bit to 1, the instruction affects the Less Than (LT) zero, Greater Than (GT) zero, Equal To (EQ) zero, and Summary Overflow (SO) bits in Condition Register Field 0.

Parameters

RA	Specifies target general-purpose register where result of operation is stored.
RS	Specifies source general-purpose register for operation.

Examples

The following code counts the number of leading zeros in the value contained in GPR 3 and places the result back in GPR 3:

# Assume GPR 3 contains 0x0061 9920.
cntlzw 3,3
# GPR 3 now holds 0x0000 0009.

Related Information

Fixed-Point Processor .

Fixed-Point Logical Instructions .