Compaq ECQD2KCTE manual Encodings, True zero, Sign Exponent Fraction Vax, Meaning Finite, Data

true zero

The value +0, represented as exactly 64 zeros in a floating-point register.

4.7.4 Encodings

Floating-point numbers are represented with three fields: sign, exponent, and fraction. The sign is 1 bit; the exponent is 8, 11, or 15 bits; and the fraction is 23, 52, 55, or 112 bits. Some encodings represent special values:

Sign	Exponent	Fraction	Vax	VAX	IEEE	IEEE
			Meaning	Finite	Meaning	Finite
x	All-1’s	Non-zero	Finite	Yes	+/–NaN	No
x	All-1’s	0	Finite	Yes	+/–Infinity	No
0	0	Non-zero	Dirty zero	No	+Denormal	No
1	0	Non-zero	Resv. operand	No	–Denormal	No
0	0	0	True zero	Yes	+0	Yes
1	0	0	Resv. operand	No	–0	Yes
x	Other	x	Finite	Yes	finite	Yes

The values of MIN and MAX for each of the five floating-point data formats are:

Data	MIN	MAX
Format
F_floating	2**–127 * 0.5	2**127 *(1.0 – 2**–24)
	(0.293873588e–38)	(1.7014117e38)
G_floating	2**–1023 * 0.5	2**1023 * (1.0 – 2**–53)
	(0.5562684646268004e–308)	(0.89884656743115785407e308)
S_floating	2**–126 * 1.0	2**127 * (2.0 – 2**–23)
	(1.17549435e–38)	(3.40282347e38)
T_floating	2**–1022 * 1.0	2**1023 * (2.0 – 2**–52)
	(2.2250738585072013e–308)	(1.7976931348623158e308)
X_floating	2**–16382*1.0	2**16383*(2.0–2**–112)
	(See below† )	(See below‡ )

†(1.18973149535723176508575932662800702e4932)

‡(3.36210314311209350626267781732175260e–4932)

Instruction Descriptions 4–65