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Section 8.2.2.2:
OCTET

immutable class OCTET < $BIT_PATTERN

Inheritance map $BIT_PATTERN

Formal Types

types

SAME = OCTET ;

OCTET = seq of BIT
inv oct ==
len oct = 8

This class is the first primitive immutable class which has eight bits, but otherwise may have any meaning. Operations for creation, conversion and individual bit testing and manipulation are provided in addition to equality testing (which is solely a test of identical bit-patterns).

External specifications

The following feature is required to be implemented for this class in accordance with the specification given in $IS_EQ of which $BIT_PATTERN is a sub-type :-


The following features are required to be implemented for this class in accordance with the specifications given by inheritance in $STR of which $BIT_PATTERN is a sub-type :-


The following feature is required to be implemented for this class in accordance with the specification given in $HASH of which $BIT_PATTERN is a sub-type :-


The following features are required to be implemented for this class in accordance with the specifications given in $BINARY of which $BIT_PATTERN is a sub-type :-


The following features are required to be implemented for this class in accordance with the specifications given in the abstract class $BIT_PATTERN :-


Octet_Bits

This reader routine provides the same value as asize - for an octet!

Octet_Bits : CARD
Formal Signature
Octet_Bits() : res : CARD
Pre-condition

Since this is a reader routine, the pre-condition is vacuously true.

Post-condition
post (res = asize(self))

This reader routine returns the number of bits contained in an octet (8!).


Octet_Max

This reader routine returns the maximum unsigned value which can be represented in an octet bit-pattern.

Octet_Max : CARD
Formal Signature
Octet_Max() : res : CARD
Pre-condition

Since this is a reader routine, the pre-condition is vacuously true.

Post-condition
post (res = 2 ** asize(self) - 1)

This reader routine returns the maximum numeric value representable as an exact unsigned number in the octet bit-pattern.


create

This creation feature returns a new octet all the bits of which are clear (ie having the value clearbit.

create : SAME
Formal Signature
create() res : SAME
Pre-condition

Because there are no arguments to this feature, the pre-condition is vacuously true.

Post-condition
post let resbits : seq of BIT be st resbits = res in
resbits = [clearbit, clearbit, clearbit, clearbit, clearbit, clearbit, clearbit, clearbit]

This routine creates a new octet value all the components of which are clear.


create

This creation routine returns a new octet in which the bit-pattern is the representation of val.

create (
val : CARD
) : SAME
Formal Signature
create2(val : CARD) res : SAME
Pre-condition
pre val <= Octet_Max
Post-condition
post card(res) = val

This routine returns a new octet which takes the value val as a bit-pattern.


create

This third creation routine returns a new octet in which the bit-pattern is the representation of the character val in eight bits.

create (
val : CHAR
) : SAME
Formal Signature
create3(val : CHAR) res : SAME
Pre-condition
pre let extra = tl CHAR.binstr(val) in
forall idx in inds extra & extra(idx) = null
Post-condition
post char(res) = val

This routine returns a new octet which takes the value val as a bit-pattern.


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Comments or enquiries should be made to Keith Hopper.
Page last modified: Wednesday, 22 November 2000.
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