Control Data Cyber 170 State Hardware Reference Manual page 79

CP Integer Arithmetic Instructions
Unpack ( X k ) t o X i and Bj
U X i Bj, Xk
This i n s t r u c t i o n r e a d s one operand from Xk, unpacks t h i s word from f l o a t i n g -
point format, and d e l i v e r s t h e c o e f f i c i e n t and exponents t o X i and B j ,
r e s p e c t i v e l y . The 60-bit word d e l i v e r e d t o X i c o n s i s t s of t h e lowest 48 b i t s
u n a l t e r e d from t h e o r i g i n a l operand p l u s t h e upper
1 2
b i t s , each equal t o t h e
o r i g i n a l s i g n b i t . This is a signed i n t e g e r equal t o t h e value of t h e
c o e f f i c i e n t i n t h e o r i g i n a l operand. The 18-bit q u a n t i t y d e l i v e r e d t o B j i s a
signed i n t e g e r equal t o t h e value of the exponent i n the o r i g i n a l operand. The
11-bit exponent f i e l d i n t h e operand i s a l t e r e d t o remove t h e b i a s and then
sign-extended t o f i l l out t h e 18-bit q u a n t i t y . The s i g n of t h e c o e f f i c i e n t i s
removed
i n
t h i s process.
Four sample s e t s of operands and unpacked 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 the o p e r a t i o n performed. These examples c o n t a i n the four
combinations of c o e f f i c i e n t s i g n and exponent sign.
( x i ) = 0000 4500 3333 2000 0077
(Xi)
=
7777 3277 4444 5777 7700
This i n s t r u c t i o n converts a number from floating-point format t o fixed-point
format. For f u r t h e r information, r e f e r t o Floating-point Arithmetic under C P
Programming i n chapter 5.