Xerox/Scientific Data Systems Sigma 5 Numbers

These number representations are used for Xerox Data Systems (XDS), previously known as Scientific Data Systems, Sigma 5 computers.

These floating point numbers are represented by one bit for the sign (S), 7 bits for the exponent, and 24 bits for the fraction.  The exponent is to the base 16 (not 2), and has a bias of 64.  Negative floating point numbers are the two's complement of the positive representation.

SINGLE PRECISION is shown below:
 
Sigma 5 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

DOUBLE PRECISION adds another 32 bits of fraction in the following 32 bits.

NOTE that the Fraction, F, is

Comparing numbers with many leading zeroes in |F| may lead to erroneous results.

INTEGER numbers are 32 bits long, and are in two's complement.