Boolean Type

f90 supports constants and expressions of Boolean type. There are no Boolean variables or arrays, and there is no Boolean type statement.

Miscellaneous Rules Governing Boolean Type

• Masking-A bitwise logical expression has a Boolean result; each of its bits is the result of one or more logical operations on the corresponding bits of the operands.

• For binary arithmetic operators, and for relational operators:

  • If one operand is Boolean, the operation is performed with no conversion.

  • If both operands are Boolean, the operation is performed as if they were integers.

• No user-specified function can generate a Boolean result, although some (nonstandard) intrinsics can.

• Boolean and logical types differ as follows:

  • Variables, arrays, and functions can be of logical type, but they cannot be Boolean type.

  • There is a LOGICAL statement, but no BOOLEAN statement.

  • A logical variable or constant represents only one value. A Boolean constant can represent as many as 32 values.

  • A logical expression yields one value. A Boolean expression can yield as many as 32 values.

  • Logical entities are invalid in arithmetic, relational, or bitwise logical expressions. Boolean entities are valid in all three.

Alternate Forms of Boolean Constants

f90 allows a Boolean constant (octal, hexadecimal, or Hollerith) in the following alternate forms (no binary). Variables cannot be declared Boolean. Standard Fortran does not allow these forms.

Octal

ddddddB, where d is any octal digit

• You can use the letter B or b.

• There can be 1 to 11 octal digits (0 through 7).

• 11 octal digits represent a full 32-bit word, with the leftmost digit allowed to be 0, 1, 2, or 3.

• Each octal digit specifies three bit values.

• The last (rightmost) digit specifies the content of the rightmost three bit positions (bits 29, 30, and 31).

• If less than 11 digits are present, the value is right-justified--it represents the rightmost bits of a word: bits n through 31. The other bits are 0.

• Blanks are ignored.

Within an I/O format specification, the letter B indicates binary digits; elsewhere it indicates octal digits.

Hexadecimal

X'ddd' or X"ddd", where d is any hexadecimal digit

• There can be 1 to 8 hexadecimal digits (0 through 9, A-F).

• Any of the letters can be uppercase or lowercase (X, x, A-F, a-f).

• The digits must be enclosed in either apostrophes or quotes.

• Blanks are ignored.

• The hexadecimal digits may be preceded by a + or - sign.

• 8 hexadecimal digits represent a full 32-bit word and the binary equivalents correspond to the contents of each bit position in the 32-bit word.

• If less than 8 digits are present, the value is right-justified--it represents the rightmost bits of a word: bits n through 31. The other bits are 0.

Hollerith

Accepted forms for Hollerith data are:

nH...	'...'H	"..."H
nL...	'...'L	"..."L
nR...	'...'R	"..."R

Above, "..." is a string of characters and n is the character count.

• A Hollerith constant is type Boolean.

• If any character constant is in a bitwise logical expression, the expression is evaluated as Hollerith.

• A Hollerith constant can have 1 to 4 characters.

Examples: Octal and hexadecimal constants.

Boolean Constant	Internal Octal for 32-bit word
0B	00000000000
77740B	00000077740
X"ABE"	00000005276
X"-340"	37777776300
X'1 2 3'	00000000443
X'FFFFFFFFFFFFFFFF'	37777777777

Examples: Octal and hexadecimal in assignment statements.

i = 1357B
j = X"28FF"
k = X'-5A'

Use of an octal or hexadecimal constant in an arithmetic expression can produce undefined results and do not generate syntax errors.

Alternate Contexts of Boolean Constants

f90 allows BOZ constants in the places other than DATA statements.

B'bbb'	O'ooo'	Z'zzz'
B"bbb"	O"ooo"	Z"zzz"

If these are assigned to a real variable, no type conversion occurs.

Standard Fortran allows these only in DATA statements.