Parallel Average Subtract Example - Intel ITANIUM ARCHITECTURE - SOFTWARE DEVELOPERS MANUAL VOLUME 3 REV 2.3 Manual

pavgsub
pavgsub — Parallel Average Subtract
( ) pavgsub1
Format: qp
( ) pavgsub2
qp
The unsigned data elements of GR
Description:
GR . The results of the subtraction are then each independently shifted to the right by
r
2
one bit position. The high-order bits of each element are filled with the borrow bits of
the subtraction (the complements of the ALU carries). To prevent cumulative round-off
errors, an averaging is performed. The low-order bit of each result is set to 1 if at least
one of the two least significant bits of the corresponding difference is 1. The signed
results are placed in GR
Figure 2-32.
GR r
GR r
16-bit Difference
Plus
Carry
Shift Right
1 Bit
GR r
3:204
= ,
r r r
1 2 3
= ,
r r r
1 2 3
.
r
1

Parallel Average Subtract Example

:
3
:
2
- - -
:
1
pavgsub2
are subtracted from the unsigned data elements of
r
3
-
Borrow
Bit
one_byte_form
two_byte_form
Shift Right 1 Bit
with Average in
Low-order Bit
Sum Bits
or
Volume 3: Instruction Reference
A9
A9