09/11/84  fortran typeless builtins

This segment describes Fortran's new typeless intrinsic functions and
how they are used.


Explanation of typeless data type:

There are six builtin functions, "and", "or", "xor", "bool", "compl",
and "fld", that return their results in a special data mode called
"typeless".  This data mode is treated as a one word bit-string (36
bits).


Typeless arithmetic:

There are no typeless variables or constants, only typeless
expressions.  Typeless entities can only exist as the result of one of
the six typeless functions and can only be combined with integer or
other typeless entities.


Typeless expressions may contain the basic mathematical operators
("+", "-", "/", and "*").  When typeless values are combined in this
way, the operations are performed in the same manner as integer
arithmetic.  As an example, the expression:

(bool (i) + 4) * 9

adds the typeless value (which is the same as the integer value) of
"i" to 4 and then multiplies the result by 9.  If "i" was, for
example, the integer 3, the value of the above expression would be the
bit-string whose integer value was 63 (3+4=7, 7*9=63).

With the arithmetic operators the result is always typeless; with
relational operators, the result is logical.


Typeless assignments:

Assignments of this data type can only be to variables one word in
length (scalar or subscripted).

Whenever the right side of an equals operation yields a typeless
result, the assignment operation is typeless.  This means that the 36
bit string representing the value on the right hand side is stored
without conversion into the location indicated by the left hand side.
The left hand side must have a real, integer, or character*4 data
type.  For example, if "r" is a real variable, the statement:

r = bool(r) + 1

adds one to the least significant bit of the real value of "r", using
an integer add, and stores the new value as a bit-string in "r".


Assignments to logical variables are allowed but are treated
differently.  The result is .TRUE.  if any bits are set, or .FALSE.
if all the bits are zero.


The individual functions:

and (a1, a2, ...)
Bit by bit logical product of two or more arguments.  All arguments
must have a one word data type.

or (a1, a2, ...)
Bit by bit logical sum of two or more arguments.  All arguments must
have a one word data type.

xor (a1, a2, ...)
Bit by bit "exclusive or" of two or more arguments.  All of the
arguments must have a one word data type.


bool (a1)
Returns the single argument as a typeless bit-string.  The argument
must have a one word data type.

compl (a1)
Returns a typeless bit-string which is the one's complement of the
single argument.  The argument must have a one word data type.


fld (i1, i2, a)
Used to manipulate bit-strings.  The first two arguments are integer
expressions where 0<= "i1" <=35, 1<= "i2" <=36, and (i1 + i2) <= 36.
The third argument must have a one word data type.  This function
extracts a field of "i2" bits from a 36 bit string represented by "a"
starting with the bit indicated by "i1" (counted from left to right
where the 0'th bit is the leftmost).  The resulting field is
right-justified and the remaining bits are set to zero.


This intrinsic function can also appear as a pseudo-variable on the
left hand side of an assignment statement.  When the fld intrinsic is
used in this manner, it must not be the first executable statement of
the program or it will be interpreted as a statement function.  The
fld pseudo-variable is defined as follows:

fld (i1, i2, a) = b

where "i1" and "i2" are integer expressions as described above; "a" is
a scalar or subscripted variable; and "b" is an expression.  The "i2"
rightmost bits of expression "b" will be inserted into "a" beginning
at bit position "i1".


Other related functions:

The following are integer functions with integer arguments that
perform bit shifting operations and are therefore related to the
typeless functions.  The first argument of these functions can be a
typeless expression.


ils (i1, i2)
The first argument (which may be either a typeless or integer
expression) is shifted left by the number of bit positions indicated
by the second argument (which is an integer expression).  The function
returns an integer value.

irs (i1, i2)
The first argument is shifted right (with sign extension) by the
number of bit positions indicated by the second argument.


ilr (i1, i2)
The first argument is rotated left by the number of bit positions
indicated by the second argument.

irl (i1, i2)
The first argument is shifted right (without sign extension) by the
number of bit positions indicated by the second argument.


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Historical Background

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This donation is made also to give evidence of the common contributions of Massachusetts Institute of Technology,
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Multics development was initiated by Massachusetts Institute of Technology Project MAC (1963-1970),
renamed the MIT Laboratory for Computer Science and Artificial Intelligence in the mid 1970s, under the leadership
of Professor Fernando Jose Corbato. Users consider that Multics provided the best software architecture 
for managing computer hardware properly and for executing programs. Many subsequent operating systems 
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Multics was distributed in 1975 to 2000 by Group Bull in Europe , and in the U.S. by Bull HN Information Systems Inc., 
as successor in interest by change in name only to Honeywell Bull Inc. and Honeywell Information Systems Inc. .

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