Control Data Cyber 170 State Hardware Reference Manual page 185

CP Programming
COEFFICIENT SIGN
BINARY POINT
r
,,,AS
I
EXPONENT
INTEGER COEFFICIENT
A
I
Figure 5-2. Floating-Point Format
Table 5-1 summarizes the configurations of bits 58 and 59 and the implications
regarding signs of the possible combinations.
Table 5-1. Bits 58 and 59 Configurations
Bit 59 Bit 58 Coefficient Sign Exponent Sign
0
1
Positive Positive
0 0 Positive Negative
1 0 Negative Positive
1 1 Negative Negative
Packing
Packing refers to the conversion of numbers in the form kBn to floating-point
format.
A
shortcut method of packing exponents can be derived by considering
the representation of -0 and
+O exponents. Assuming a positive coefficient, 0
exponents are packed as follows:
+O
exponent: 2000x,...,x
-0 exponent: 1777x,...,x
Since positive exponents are expressed in true form, begin with a
bias of
2000
(4) aid add the magnitude of the exponent. The range of positive exponents is
0000 through 1777. In packed form, the range is 2000 through 3777.
When the coefficient is negative, the packed positive exponent is complemented
to become 5777 through 4000.