Control Data Cyber 170 State Hardware Reference Manual page 104

CP Floating-Point Arithmetic Instructions
Floating Product
40i
j k
Floating product of (Xj) and (Xk) t o X i FXi
X j
*
Xk
This i n s t r u c t i o n reads 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
floating-point 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 X j and Xk.
These operands a r e i n
floating-point 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
delivered t o X i i n floating-point 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, the r e s u l t i s
not normalized,
The two operands a r e unpacked from floating-point format.
The exponents a r e
added with a c o r r e c t i o n f a c t o r t o determine the 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 a s signed i n t e g e r s t o form a 96-bit i n t e g e r
product.
The upper h a l f of t h i s product
is
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 . I f t h e o r i g i n a l operands a r e normalized and t h e product has
only 95 s i g n i f i c a n t b i t s , a 1-bit l e f t s h i f t i s 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 is reduced by one count i n t h i s case.
I f both operands a r e not normalized, the r e s u l t i n g double-precision product h a s
l e s s than 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 are read from t h e double-precision product
r e g i s t e r . Leading zeros 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 floating-point c a l c u l a t i o n s where rounding of
operands i s not d e s i r e d , such a s i n multiple-precision a r i t h m e t i c and i n
c a l c u l a t i o n s involving e r r o r a n a l y s i s .
I n f i n i t e (3777xxx
...
x o r ~ O O O X X X . . . ~ )
o r i n d e f i n i t e (1777xxx
...
x o r 6000xxx...x) operands cause corresponding e x i t
conditions 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 chapter 5.