Intel ITANIUM ARCHITECTURE - SOFTWARE DEVELOPERS MANUAL VOLUME 1 REV 2.3 Manual page 1779

4.7.1.4 Real Number and Non-Number Encodings
A variety of real numbers and special values can be encoded in the processor's
floating-point format. These numbers and values are generally divided into the
following classes:
• Signed zeros
• Denormalized finite numbers
• Normalized finite numbers
• Signed infinities
• NaNs
• Indefinite numbers
(The term NaN stands for "Not a Number.")
Figure 4-10
real number continuum. The encodings shown here are for the IEEE single-precision
(32-bit) format, where the term "S" indicates the sign bit, "E" the biased exponent, and
"F" the fraction. (The exponent values are given in decimal.)
The processor can operate on and/or return any of these values, depending on the type
of computation being performed. The following sections describe these number and
non-number classes.
4.7.1.5 Signed Zeros
Zero can be represented as a +0 or a 0 depending on the sign bit. Both encodings are
equal in value. The sign of a zero result depends on the operation being performed and
the rounding mode being used. Signed zeros have been provided to aid in
implementing interval arithmetic. The sign of a zero may indicate the direction from
which underflow occurred, or it may indicate the sign of an that has been
reciprocated.
4.7.1.6 Normalized and Denormalized Finite Numbers
Non-zero, finite numbers are divided into two classes: normalized and denormalized.
The normalized finite numbers comprise all the non-zero finite values that can be
encoded in a normalized real number format between zero and . In the format shown
in Figure
ranging from 1 to 254
Volume 4: IA-32 SSE Instruction Reference
shows how the encodings for these numbers and non-numbers fit into the
4-10, this group of numbers includes all the numbers with biased exponents
(unbiased, the exponent range is from 126
10
to +127 ).
10 10
4:477