Control Data Cyber 170 State Hardware Reference Manual page 105

CP Floating-Point Arithmetic Instructions
Round f l o a t i n g product of (Xj) and
(Xk) t o
X i
This i n s t r u c t i o n r e a d s operands from two X r e g i s t e r s , o p e r a t e s on them t o form
a rounded f l o a t i n g - p o i n t product, and d e l i v e r s t h i s r e s u l t t o a t h i r d X
r e g i s t e r . The operands f o r t h i s i n s t r u c t i o n a r e i n Xj and Xk.
These operands
a r e i n f l o a t i n g - p o i n t format and a r e not n e c e s s a r i l y normalized.
The r e s u l t i s
d e l i v e r e d t o Xi in f l o a t i n g - p o i n t format.
I f both operands a r e normalized, t h e
r e s u l t i s a l s o normalized. I f both operands a r e not normalized, t h e r e s u l t i s
n o t normalized.
The two operands a r e unpacked from f l o a t i n g - p o i n t format. The exponents a r e
added w i t h ' a c o r r e c t i o n f a c t o r t o determine t h e exponent f o r t h e r e s u l t . The
c o e f f i c i e n t s a r e m u l t i p l i e d as signed i n t e g e r s t o form a 96-bit i n t e g e r
product.
A rounding b i t is added t o b i t p o s i t i o n 46 of t h i s product.
The
upper half of t h i s product i s e x t r a c t e d t o form t h e c o e f f i c i e n t f o r t h e
r e s u l t . If t h e o r i g i n a l operands a r e normalized and t h e product has o n l y 95
s i g n i f i c a n t b i t s , a l - b i t l e f t s h i f t is done t o normalize t h e r e s u l t
c o e f f i c i e n t . The r e s u l t i n g exponent i s reduced by one count i n t h i s case.
If both operands a r e not normalized, t h e r e s u l t i n g double-precision product has
l e s s t h a n 96 s i g n i f i c a n t b i t s . N o t e s t
i s
made f o r t h e p o s i t i o n of t h e most-
s i g n i f i c a n t b i t .
The upper
48
b i t s a r e r e a d from t h e double-precision product
r e g i s t e r . Leading z e r o s occur i n t h i s r e s u l t c o e f f i c i e n t .
This i n s t r u c t i o n i s used i n s i n g l e - p r e c i s i o n , f l o a t i n g - p o i n t c a l c u l a t i o n s . For
m u l t i p l e - p r e c i s i o n c a l c u l a t i o n s , t h e 40 and 42 i n s t r u c t i o n s must be used.
I n f i n i t e (37779xx.. .x o r 4000rmx.. .x) o r i n d e f i n i t e (1777xxx.. . x
or
6000xxx
...
x ) operands cause corresponding e x i t c o n d i t i o n s t o s e t i n t h e CP f o r
e x i t mode a c t i o n .
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.