Sharp MZ-5500 - Page 112

Complement of 2 is used to represent binary integer of 16 bits, 32 bits, or
64 bits, the most significant bit being a sigh bit.
A BCD 18 digits are used to represent decimal integer, the most significant
bit being a sign bit, and when the number becomes .negative , only th e s i gn
is chang ed with rest of figure not affected. All bits of the mo st
significant byte except the sign bit are dis ~ egarded when l ~ ad e d and
treated as 0 when stored. •
Real Ilumber is represented in either of 32 bits, 64 bits, or 80 bi ts ,
havin g a sign bit, exponentia1 bits, and mantissa bits. The tru e va l ue of
the mantissa can be obtained in the following manner, assuming th e e xpone nt
as E and mantissa as F.
(-1) S . (2 (E-BIAS) ) . ~l. F)
BIAS
7FH (short real number)
d
3FFH (long real number)
3FFFll (temporary real nurnber)
A negative real number is sirnply attached with a negative sign to the reell
nurnber. The exponential part is provided for easier data comparison and
has been added with the above mentioned bias. The following is an example
to compare.
+ 5 00000101
BIAS ) ~OOO100
-40 11011000
+7FH 01010111
+10 00001010
BIAS) 10~OOI
+21
00010101
+7FH 10 1 100
- 7
11111001
BIAS
~
Olll~OOO
-11
11110101
+7FH
0111 100
If not biased, it needs to distinguish comparisü~between the same signs ~d
different signs. But, when biased, comparison can be done with a first
different bit by making comparison from high order bit, sjmilar as the
unsigned binar)' integer.
/,; l
As the integer part is 1 for the rnantissa, the maximum effective digits are
maintained for a numb e r sma11er than 1. Table 1 sh o ws an exampl e 1 10 W t h E'
real number 178.125 (decima1) is stored when represent ed in a fo rm af sl10 r t
ward length real number by the 8087.
Decirnal
178.125
Exponential type decimal L.78125E2
Exponential type binary 1~0110010001E111
Exponelltial type binary, bias , ed
1~0110010001E10000110
8087 short word real number
Sign I Biased expl '
o _ 10000110 0110010001000000000000080
loq