dlmzb
Determine Leftmost Zero Byte
Preliminary PPC440x5 CPU Core User’s Manual
instrset.fm.
September 12, 2002 Page 309 of 589
dlmzb
determine left most zero byte
d ← (RS) || (RB)
i, x, y ← 0
do while (x < 8) ∧ (y = 0)
x← x + 1
if di:i + 7= 0 then
y← 1
else
i← i + 8
(RA) ← x
XER[TBC] ← x
if Rc = 1 then
CR[CR0]3←XER[SO]
if y = 1 then
if x < 5 then
CR[CR0]0:2 ← 0b010
else
CR[CR0]0:2 ← 0b100
else
CR[CR0]0:2 ← 0b001
The contents of registers RS and RB are concatenated to form an 8-byte operand. The operand is searched
for the leftmost byte in which each bit is 0 (a 0-byte).
Bytes in the operand are numbered from left to right starting with 1. If a 0-byte is found, its byte number is
placed into XER[TBC] and register RA. Otherwise, the number 8 is placed into XER[TBC] and register RA.
If the Rc field contains 1, XER[SO] is copied to CR[CR0]3 and CR[CR0]0:2 are updated as follows:
• If no 0-byte is found, CR[CR0]0:2 is set to 0b001.
• If the leftmost 0-byte is in the first 4 bytes (in the RS register), CR[CR0]0:2 is set to 0b010.
• If the leftmost 0-byte is in the last 4 bytes (in the RB register), CR[CR0]0:2 is set to 0b100.
Registers Altered
• XER[TBC]
•RA
• CR[CR0]if Rc contains 1
Architecture Note
This instruction is implementation-specific and programs which use this instruction may not be portable to
other PowerPC Book-E implementations. See Instruction Set Portability on page 250.
dlmzb RA, RS, RB Rc=0
dlmzb. RA, RS, RB Rc=1
31 RS RA RB 78 Rc
0 6 11 16 21 31