Xerox/Scientific Data Systems Sigma 9

Xerox/Scientific Data Systems FLOATING POINT numbers are represented by one or two 32-bit words. In the single 32-bit version, the first bit is for the sign (S), 7 bits are for the exponent, and 24 bits are for the fraction. Since the exponent is to the base 16, some of the exponential value may be assumed by the fraction, at the cost of some precision.

There are two floating point formats: short and long . Short is shown below:

Xerox/Scientific Data Systems Short Floating Point Format
S Exponent Fraction
31
30
29
28
27
26
25
24
23
22
21
20
19
18
17
16
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
0

Long floating point is the same, with the addition of another word (32 bits) of fraction, but see RANGE, below.  The first 32 bits are the same as above.

EXPONENT (E): To the base 16, with a bias of 64.

ZERO: A positive floating-point number with a fraction of zero and a characteristic of zero is a "true" zero.
A positve floating-point number with a fraction of zero and a non-zero characteristic is an "abnormal" zero.

NEGATIVE FLOATING POINT NUMBERS:  Same as positives, but in two's complement.

RANGE:  The value of the number N is N = F x 16E-64 ,  where

 

Note that the lowest non-zero values of |F| may have significantly reduced precision!


INTEGER numbers are represented in two's complement.