Reporting Facility Rules for Coding › Bit Masks

Bit Masks

In coding a Reporting Facility program, you may need to test the contents of a single byte against a mask. When using a mask in a logical expression, code it in the following format:

►►─ B'testbits' ──────────────────────────────────────────────────────────────►◄

'testbits'

Specifies the mask to be tested. It is comprised of one to eight 1s, 0s, or Xs. Positioning in the mask corresponds to bits 0—7, from left to right, of the byte to be tested against.

• 1 in the mask means that the corresponding bit in the string will be tested to be ON.
• 0 in the mask means that the corresponding bit in the string will be tested to be OFF.
• X in the mask means that the corresponding bit in the string is NOT TO BE TESTED.

Note the following:

• Reference bit masks only in logical expressions on GOTO or SELECT commands. You must define the first operand in the logical expression as a bit string.
• The Reporting Facility compiler requires at least one bit position to be tested in a mask specification, that is, at least one 1 or 0 must be specified in the mask.
• You can never print a bit string field. You can only test it against a mask.
• Compare bit string fields with a bit mask only in an EQUAL or NOT EQUAL relationship.
• Consider the bit mask test to be true if the tested byte conforms to the bit mask pattern; otherwise, a false condition exists.
• The system assumes that bit positions not specified on the right side of the mask are not to be tested.
• The following table shows both valid and invalid bit mask comparisons based on these commands:

  DEFINE BIT-STRING 27 S
  GOTO START WHEN (BIT-STRING EQ mask)