MILITARY STANDARD 1753

FORTRAN, DoD Supplement To
American National Standard X3.9-1978

November 9, 1978

TABLE OF CONTENTS

1.0 SCOPE
2.0 ADDED FACILITIES
2.1 END DO STATEMENT
2.2 DO WHILE STATEMENT
2.3 INCLUDE STATEMENT
2.4 IMPLICIT STATEMENT
2.5 READ AND WRITE PAST END-OF-FILE
2.6 BIT FIELD MANIPULATIONS
2.6.1 BINARY PATTERN PROCESSING
2.6.1.1 Logical Operations
2.6.1.1.1 Inclusive OR
2.6.1.1.2 Logical AND
2.6.1.1.3 Logical Complement
2.6.1.1.4 Exclusive OR
2.6.1.2 Shift Operations
2.6.1.2.1 Logical Shift
2.6.1.2.2 Circular Shift
2.6.2 BIT SUBFIELDS
2.6.2.1 Bit Extraction
2.6.2.2 Bit Move Subroutine
2.6.3 BIT PROCESSING
2.6.3.1 Bit Testing
2.6.3.2 Set Bit
2.6.3.3 Clear Bit
2.6.4 BIT CONSTANTS

1.0 SCOPE

This Supplement contains the syntax and semantics for those facilities necessary to the operating needs of the DOD Departments and Agencies. Facilities contained herein are to be provided as additions to ANSI X3.9-1978 without altering the form or function of the standard facilities. The terminology used herein corresponds to that in ANSI X3.9-1978.

2.0 ADDED FACILITIES

2.1 END DO STATEMENT

The END DO statement must only be used as the terminal statement of a DO-loop and has no other effect. The form of the END DO statement is:

     END DO
If END DO is used as the terminal statement of an ANSI X3.9-1978 DO statement, the END DO statement must be labeled.

2.2 DO WHILE STATEMENT

The DO WHILE statement allows execution of a DO-loop while a logical expression is true. The form of the DO WHILE statement is:

     DO [ label [,] ] WHILE (logical expression)
The logical expression is evaluated and tested at the beginning of the DO-loop.

Each DO WHILE DO-loop must be terminated by a separate END DO statement.

The label is an option to the programmer. If the label is used in the DO WHILE statement, the END DO statement that terminates the DO-loop must be labeled with the same label.

The rules for transfers into the range of the DO-loop are the same as for the current standard DO-loop.

2.3 INCLUDE STATEMENT

The INCLUDE statement provides the capability to copy source code from a file into a compiler source stream. The form of the INCLUDE statement is:

     INCLUDE filename
The INCLUDE statement must be contained on one line.

The filename identifies the source code to be copied into the source stream. The filename can be processor dependent.

An INCLUDE statement will initiate copying at the beginning of the file. The file must not be empty and the first line that is not a comment line must not be a continuation line.

Implementation of the INCLUDE statement must permit the concept of nonrecursive nesting (i.e., the included copy may contain another INCLUDE statement).

2.4 IMPLICIT STATEMENT

The IMPLICIT statement is extended to provide the capability to the programmer to void all default implicit types except for the intrinsic functions. An additional form of the IMPLICIT statement is:

     IMPLICIT NONE
If the IMPLICIT NONE appears in a program unit, no other IMPLICIT statements may appear in the same program unit.

2.5 READ AND WRITE PAST END-OF-FILE

The processor must provide a facility that permits reading and writing to continue past an endfile record on an unlabeled magnetic tape sequential file. Reading past an endfile record is not permitted if the READ statement does not contain and END= or an IOSTAT= specifier. The processor may require execution of a special subroutine or statement before it permits such reading or writing.

2.6 BIT FIELD MANIPULATIONS

Bit manipulation capability is provided through a standard set of external functions. This capability is compatible with similar functions included in ANSI/ISA S61.1-1976. In each of the defined functions, it is assumed that the integer arguments m and n are represented in binary form.

2.6.1 BINARY PATTERN PROCESSING

2.6.1.1 Logical Operations

Logical operations provided are the Boolean functions OR, AND, EOR and NOT. These operations are provided as integer external functions. The implicit type for OR, AND, and EOR is indicated by the use of I as the first letter of the function name. Their arguments, m and n, can be integer constants, integer variables, integer array elements, or integer expressions. After execution of the functions, the arguments remain unchanged. The operations are performed on all corresponding bits of the two operands.

2.6.1.1.1 Inclusive OR

Function reference: IOR (m, n)

The arguments, m and n, are combined according to the following truth table:

                m = 0 1 0 1
                n = 0 0 1 1
                ___________
Function value    = 0 1 1 1

2.6.1.1.2 Logical AND

Function reference: IAND (m, n)

The arguments, m and n, are combined according to the following truth table:

                m = 0 1 0 1
                n = 0 0 1 1
                ___________
Function value    = 0 0 0 1

2.6.1.1.3 Logical Complement

Function reference: NOT (m)

The argument m is logically complemented according to the following truth table:

                    m = 0 1
                    _______
Function value        = 1 0

2.6.1.1.4 Exclusive OR

Function reference: IEOR (m, n)

The arguments, m and n, are combined according to the following truth table:

                m = 0 1 0 1
                n = 0 0 1 1
                ___________
Function value    = 0 1 1 0

2.6.1.2 Shift Operations

The shift operations provided are logical and circular. The shift operations are implemented as integer functions. The arguments may be integer constants, integer variables, integer array elements, or integer expressions. The arguments m and k are as follows:

If the absolute value of the shift count is greater than the number of bits in a numeric storage unit, the result is undefined. The arguments are not changed by the shift operations.

2.6.1.2.1 Logical Shift

Function reference: ISHFT (m, k)

All bits representing the argument m are shifted k places. Bits shifted out from the left end or the right end, as the case may be, are lost. Zeros are shifted in from the opposite end.

2.6.1.2.2 Circular Shift

Function reference: ISHFTC (m, k, ic)

The rightmost ic bits of the argument m are shifted circularly k places; i.e., the bits shifted out of one end are shifted into the opposite end. No bits are lost. The unshifted bits of the result are the same as the unshifted bits of the argument m. The absolute value of the argument k must be less than or equal to ic. The argument ic must be greater than or equal to one and less than or equal to the number of bits in a numeric storage unit.

2.6.2 BIT SUBFIELDS

Bit subfields are referenced by specifying a bit position and a length. Bit positions within a numeric storage unit are numbered from right to left and the rightmost bit position is numbered 0. Bit fields may not extend from one numeric storage unit into another numeric storage unit, and the length of a field must be greater than zero.

2.6.2.1 Bit Extraction

Function reference: IBITS (m, i, len)

where m, i, len are integer expressions

This function extracts a subfield of len bits from m starting with bit position i and extending left for len bits. The result field is right justified and the remaining bits are set to zero. The value of i+len must be less than or equal to the number of bits in a numeric storage unit.

2.6.2.2 Bit Move Subroutine

CALL MVBITS (m, i, len, n, j)

This subroutine moves len bits from positions i through i+len-1 of argument m to positions j through j+len-1 of argument n. The portion of argument n not affected by the movement of bits remains unchanged. All arguments are integer expressions except n must be a variable or array element. Arguments m and n are permitted to be the same numeric storage unit. The values of i+len and j+len must be less than or equal to the number of bits in a numeric storage unit.

2.6.3 BIT PROCESSING

Individual bits of a numeric storage unit can be tested and changed with the following routines for bit processing. The functions have two arguments n and i which are integer expressions.

If i is negative or greater than the number of bits in a numeric storage unit, the result of the function is undefined.

2.6.3.1 Bit Testing

Function reference: BTEST (n, i)

This function is a logical function. The ith bit of argument n is tested. If it is 1, the value of the function is .TRUE.; if it is 0, the value of the function is .FALSE.

2.6.3.2 Set Bit

Function reference: IBSET (n, i)

The result of the IBSET function is equal to the value of n with the ith bit set to a 1.

2.6.3.3 Clear Bit

Function reference: IBCLR (n, i)

The result of the IBCLR function is equal to the value of n with the ith bit set to a 0.

2.6.4 BIT CONSTANTS

The following two forms of bit constants are permitted in DATA statements:

               O'di ... dn'
 
               Z'hi ... hn'
where di are octal digits and hi are hexadecimal digits with A - F representing the decimal equivalent of 10 - 15. These constants are right-justified and may be associated only with integer entities. These constants may appear only in DATA statements.

(NOTE: For reasons of efficiency, it is desirable that the bit manipulation capabilities also be available as in-line code.)

Stephen Berrick
Comments to author: sberrick@eos.hitc.com

Revised: March 7, 1997