Vector population count
unit
Although the
CRAY-1
does
not include a vector population
unit
as
a standard
feature,
such a
unit
is
present
when
the Vector Population
Instructions
Option
is
installed.
The
vector population count
unit
recognizes the
vector population count
instruction,
174ij1
and
the vector population
count
parity
instruction,
174ij2. Because implementation
of
these
instruc-
tions
requires modifications to the format
of
the vector reciprocal
approximation
instruction,
some
of
the
restrictions
for the reciprocal
approximation
unit
hold
true
for the vector population
instructions.
FLOATING
POINT
FUNCTIONAL
UNITS
The
three
floating
point functional
units
perform
floating
point arithmetic
for
both
scalar
and
vector operations.
When
executing a
scalar
instruction,
operands are obtained
from
S
registers
and
the
result
is
delivered to
an
S
register.
When
executing
most
vector
instructions,
operands are obtained
from
pairs
of V
registers
or
from
a V
register
and
an
S
register
and
the
results
are delivered to a V
register.
The
reciprocal
instruction,
which
has
only
one
input operand,
is
an
exception.
A
floating
point
unit
is
reserved during execution of a vector
instruction.
Information
on
floating
point out-of-range conditions
is
contained in the
subsection
entitled
Floating Point Arithmetic.
Floating point
add
unit
The
floating
point
add
unit
performs addition or
subtraction
of
64-bit
operands in
floating
point format.
The
unit implements
instructions
062,
063,
and
170
through 173. Functional
unit
time
is
six
clock periods.
A
result
is
normalized
even
if
the operands are unnormalized.
Out-of-range exponents are detected
as
described under Floating Point
Arithmetic.
2240004
3-18
E
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