Full-Precision Numbers; Short-Precision Numbers - HP 9835A Programming Manual

The Processor and the Operating System
31
Full-Precision Numbers
Full-precision numeric values are stored as 12-digit, BCD (Binary Coded Decimal), floating
point numbers. They occupy four words each. The first word contains the sign of the exponent,
a two's-complement IO-bit exponent, and the sign of the mantissa. The other three words
contain the twelve mantissa digits, 4 to each word. The words look like this -
15 14 13 12 11 10 9 8 7 6 5 4 3 2 OBit
Exp
I
I I I I I I
I I
I
I I
I I
I~an
Sign!
Exponent
o
0
o
0
0 Sigr
01
(most signHicant digit)
02 03 04
05 06 07 De
012
09 010 011
(least significant)
The exponent is always adjusted during arithmetic routines so that there is an implied decimal
point following 01. Thus, every mantissa value looks like -
Short-Precision Numbers
Short-precision numeric values are stored as 6-digit, BCD floating point numbers. Unlike
full-precision, they occupy two words each instead of four. The first word contains a 7 -bit
exponent, the sign of the mantissa and the two most significant mantissa digits. The second
word contains the remaining four mantissa digits. The words look like this -
15 14 13 12 11 10 9 8 7 6 5 4 3 2 OBit
Exp:
I
I
I
I I
I~an
I I I
1 1 I
Sign!
Exponent Sign
01
02
03
I
04 05 06
As with full-precision, the exponent is stored in two's complement form and the implied deci-
mal point follows 01.
If you are unfamiliar with BCD arithmetic or need a refresher in floating point operations, it is
suggested that you refer to Chapter 5.