HP-UX Floating-Point Guide

Glossary 233
Glossary
and 23 bits for the fraction. See
also double-precision, quad-
precision.
SNaN See signaling NaN
(SNaN).
square root One of the basic
operations defined by the IEEE
standard.
static variable A variable that
retains its value between
invocations of the routine in which
it is declared. From a performance
standpoint, static variables are
costly because they prohibit the
compiler from making certain
types of optimizations.
sticky bits See exception flags.
subnormal See denormalized
value.
subtraction One of the basic
operations defined by the IEEE
standard.
sudden underflow mode See
flush-to-zero mode.
tiling Rearranging the
implementation of your algorithms
to process as much data as possible
while the data is resident in the
cache so as to minimize the
number of times the data must be
re-cached later. See also cache
aliases.
Translation Lookaside Buffer
(TLB) A hardware unit that
serves as a cache for virtual-to-
absolute memory address
mapping.
trap A change in a program’s flow
of control due to the occurrence of
an exception condition.
trap handler A routine that is
invoked whenever a particular
exception condition is detected,
if the trap is enabled.
ULP (Unit in the Last
Place) The rightmost bit of a
floating-point representation.
ULPs measure the distance
between two numbers in terms of
their representation in binary. One
ULP is the distance from one value
to the next representable value in
the direction away from 0. See also
precision.
underflow condition The
exception condition that occurs
when a floating-point operation
attempts to produce a result that
may suffer extraordinary loss of