Intel ITANIUM ARCHITECTURE - SOFTWARE DEVELOPERS MANUAL VOLUME 1 REV 2.3 Manual page 1100

pavg — Parallel Average
( ) pavg1
Format: qp
( ) pavg1.raz
qp
( ) pavg2
qp
( ) pavg2.raz
qp
The unsigned data elements of GR
Description:
The results of the add are then each independently shifted to the right by one bit
position. The high-order bits of each element are filled with the carry bits of the sums.
To prevent cumulative round-off errors, an averaging is performed. The unsigned
results are placed in GR
The averaging operation works as follows. In the normal_form, the low-order bit of
each result is set to 1 if at least one of the two least significant bits of the
corresponding sum is 1. In the raz_form, the average rounds away from zero by adding
1 to each of the sums.
Figure 2-30.
GR r
3
GR r
2
16-bit Sum
Plus
Carry
Shift Right
1 Bit
GR r
1
Volume 3: Instruction Reference
= ,
r r r
1 2 3
= ,
r r r
1 2 3
= ,
r r r
1 2 3
= ,
r r r
1 2 3
.
r
1
Parallel Average Example
:
:
+ + +
:
pavg2
normal_form, one_byte_form
raz_form, one_byte_form
normal_form, two_byte_form
raz_form, two_byte_form
are added to the unsigned data elements of GR
r
2
+
Carry
Bit
pavg
A9
A9
A9
A9
r
3
Shift Right 1 Bit
with Average in
Low-order Bit
Sum Bits
or
3:201
.