Control Data Cyber 170 State Hardware Reference Manual page 78

CP Integer Arithmetic Instructions
l nteger Pack/Unpack
2 7 i j k Pack (Xk) and (Bj) t o X i PXi B j
,
Xk
This i n s t r u c t i o n r e a d s t h e c o n t e n t s of Xk and B j , packs them i n t o a s i n g l e word
i n f l o a t i n g - p o i n t format, and d e l i v e r s t h i s r e s u l t t o X i . The c o e f f i c i e n t
f o r
t h e value i n X i i s obtained from t h e c o n t e n t of Xk, which is t r e a t e d as a
signed i n t e g e r . The exponent f o r t h e v a l u e i n X i i s obtained from t h e c o n t e n t
of B j , which i s t r e a t e d a s a signed i n t e g e r .
The lowest-order 48 b i t s i n X i a r e copied d i r e c t l y from t h e lowest-order 48
b i t s i n Xk. The s i g n b i t i n X i
is
copied d i r e c t l y from t h e s i g n b i t i n Xk.
The exponent f i e l d i n X i
i s
derived from t h e v a l u e i n Bj by e x t r a c t i n g t h e
lowest-order 1 1 b i t s i n Bj and modifying t h i s q u a n t i t y f o r exponent b i a s and
c o e f f i c i e n t sign.
Four sample s e t s of operands and packed r e s u l t s a r e l i s t e d i n o c t a l n o t a t i o n t o
i l l u s t r a t e t h e o p e r a t i o n performed. These examples c o n t a i n t h e f o u r combina-
t i o n s of c o e f f i c i e n t s i g n and exponent sign.
( X i ) =
2034 4500 3333 2000 0077
(Xi) = 5743 3277 4444 5777 7700
(Bj) =
77 7743
(Xi)
=
6034 3277 4444 5777 7700
This i n s t r u c t i o n c o n v e r t s a number i n fixed-point format t o f l o a t i n g - p o i n t
format. For f u r t h e r information, r e f e r t o Floating-point Arithmetic under
CP
Programming i n c h a p t e r 5 .