COMPUTE - bit_exp

Syntax

[COMPUTE] result = [BIT-NOT] operand1
                   [{BIT-AND|BIT-OR|BIT-XOR} [BIT-NOT] operand2
                   [{BIT-AND|BIT-OR|BIT-XOR} [BIT-NOT] operand3
                   ...  ]].

Effect

In a bit expression, an operand operand1 can be linked with one or more operands - operand2, operand3, and so on - using bit operators; parentheses are possible. Bit expressions can only be used in the COMPUTE statement.

The operands operand can be byte-type data objects, functional methods with byte-type return values, or compound bit expressions. The bit operators BIT-AND, BIT-OR, and BIT-XOR link two adjacent operands. When the expression is evaluated, a byte-type value is calculated and linked with the next adjacent operand. The priority of the link depends on the operators that are used; if you use functional methods, the same applies as described for arithmetic expressions.

You can specify the bit operator BIT-NOT one or more times before an operand to negate the value of the operand. If BIT-NOT is specified an even number of times, the operand remains unchanged. An odd number of uses negates the operand.

Note

If a single data object is specified as an operand without a preceding bit operator BIT-NOT, this is not a complete bit expression. In this case, the COMPUTE statement has the same effect as the MOVE statement.

Example

Bit sequences are an efficient way of mapping set operations. If a set contains n elements, the existence of an element i in n can be represented by a 1 at the position of i in a byte-type field. You can use the SET BIT statement, amongst others, to add an element to the set. The operators BIT-AND, BIT-OR, and BIT-XOR can then be used to calculate the average quantity, the union quantity, and the symmetrical difference of different sets.

In the following example, the attributes of person groups - for example - are mapped in the fields p1, p2, p3 of the type x. The bit operator BIT-AND is then used to determine which attributes are shared by all people. The result shows that only the eighth attribute is shared.

DATA:
  res TYPE x LENGTH 1,
  p1  TYPE x LENGTH 1 VALUE '5B',    "01011011
  p2  TYPE x LENGTH 1 VALUE '13',    "00010011
  p3  TYPE x LENGTH 1 VALUE 'A5'.    "10100101

res = p1 BIT-AND p2 BIT-AND p3. "00000001

Exceptions

Non-Catchable Exceptions