HLASM Language Reference

DC Instruction
No boundary alignment, according to constant type, is provided (see “Alignment
of Constants” on page 129).
Its value must not exceed the maximum length allowed for the various types of
constant defined.
| The length modifier must not truncate double-byte data in a C-type constant,
| except for bit-length modifiers.
The length modifier must be a multiple of 2 in a G-type or CU-type constant.
When no length is specified, for character and graphic constants (C and G),
hexadecimal constants (X), binary constants (B), and decimal constants (P and Z),
the whole constant is assembled into its implicit length.
Bit-Length Modifier: The length modifier can be specified to indicate the number
of bits into which a constant is to be assembled. The bit-length modifier is written
as L.n where n is either a decimal self-defining term, or an absolute expression
enclosed in parentheses. It must have a positive value. Such a modifier is
sometimes called a “bit-length” modifier, to distinguish it from a “byte-length”
modifier. You may not combine byte-length and bit-length modifiers. For example, a
12-bit field must be written L.12, not L1.4.
The value of n must lie between 1 and the number of bits (a multiple of 8) that are
required to make up the maximum number of bytes allowed in the type of constant
being defined. The bit-length modifier can never be used with the CU-, G-, S-, V-,
R-, J- and Q-type constants, and cannot be used with the A-type or Y-type constant
if the operand is simply or complexly relocatable.
When only one operand and one nominal value are specified in a DC instruction,
the following rules apply:
1. The bit-length modifier allocates a field into which a constant is to be
assembled. The field starts at a byte boundary and can run over one or more
byte boundaries, if the bit length is greater than 8.
If the field does not end at a byte boundary and if the bit length is not a
multiple of 8, the remainder of the last byte is filled with binary zeros. For
example, DC FL.12'-1' generates X'FFF'.
2. The nominal value of the constant is assembled into the field:
a. Starting at the high order end for the C-, E-, D-, and L-type constants
b. Starting at the low-order end for the remaining types of constants that
support a bit-length modifier
3. The nominal value is padded or truncated to fit the field (see “Padding and
Truncation of Values” on page 130).
| Note that “padding” is not the same as “filling.” In padding, the designated bit
| field is completed according to the rules for the constant type. Filling is always
| binary zeros placed at the right end of an incomplete byte.
| C-type character constants are padded with EBCDIC spaces (hexadecimal
| X'40', and CA-type character constants are padded with ASCII spaces
| (hexadecimal X'20'). Other constant types are padded either by sign
| extension or with zeros, according to the type of the constant.
Chapter 5. Assembler Instruction Statements 137