cntlzw

Count Leading Zeros Word

cntlzw RA, RS

Counts the number of consecutive 0 bits starting from bit 32 (MSB of the low word).

Details

The cntlzw instruction counts the number of consecutive zero bits starting at bit 32 of register RS and places this count into register RA. The result ranges from 0 to 32, inclusive. If Rc is set to 1, CR field 0 is updated to reflect the result.

Pseudocode Operation

n <- 0; while RS[32+n] = 0 do n <- n + 1; RA <- n

Programming Note

When Rc=1 (dot form), CR0 is updated with the signed comparison of the result against zero (LT, GT, EQ) and the current SO bit from XER.

Example

cntlzw r3, r4

Encoding

Binary Layout
31
0
RS
6
RA
11
00000
16
000011010
21
Rc
31
 
Format X-form
Opcode 0x7C000034
Extension Base
Registers Altered CR0

Operands

  • RA
    Target Register
  • RS
    Source Register