COMPUTATION
SECTION
The
computation section contains
instruction
buffers,
reqisters
and
functional units
which
operate together to execute a
program
of
instructions
stored in
memory.
Arithmetic operations are
either
integer or floating point. Inteqer
arithmetic
is
performed in two's
complement
mode.
Floating point
quantities
have
signed-magnitude representation.
The
CRAY-l
executes
128
operation
codes
as
either
16-bit
(one
parcel) or
32-bit (two-parcel)
instructions.
Operation
codes
provide for both
scalar
and
vector processinq.
Floating point
instructions
provide for addition, subtraction, multi-
plication,
and
reciprocal approximation.
The
reciprocal
npproxi~ation
instruction
allows for the computation of a floating divide operation
using a multiple
instruction
sequence.
Integer or fixed point operations are provided
as
follows: integer
addition, integer
subtraction,
and
integer
multiplication.
An
integer
multiply operation produces a 24-bit
result;
additions
and
subtractions
produce
either
24-bit or 64-bit
results.
No
integer divide
instruction
is
provided
and
the operation
is
accomplished through a software
algorithm using
floating
point hardware.
The
instruction
set
includes
Boolean
operations for
OR,
AND,
and
exclusive
OR
and
for a mask-controlled
merqe
operation.
Shift
operations allow the
manipulation of
either
64-bit
or 128-bit operands to produce
64-bit
results.
~'ith
the exception of 24-bit integer arithmetic,
all
operations
are
implemented
in vector
as
well
as
scalar
instructions.
The
inteqer
product
is
a
scalar
instruction
designed for index
calculation.
Full
indexing
capability
allows the
proarammer
to index throughout
memory
in
either
scalar
or vector
modes.
The
index
may
be
positive or negative in
either
mode.
This allows matrix operations in vector
mode
to
be
performed
on
rows
or the diagonal
as
well
as
conventional column-oriented operations.
Each
functional
unit
implements
an
algorithm or a portion of the
instruction
set.
Units are independent
and
are
fully
seqmented. This
means
that
a
new
set
of operands for unrelated computation
may
enter a functional
unit
each
clock period.
2240004
1-4 E
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