HLASM: V1R6 Language Ref

DC instruction—Fixed-point constants2. The exponent must lie within the permissible range (see ▌4▐ in Table 26). If anexponent modifier is also specified, the algebraic sum (see ▌5▐ in Table 26) ofthe exponent and the exponent modifier must lie within the permissible range.Some examples of the range of values that can be assembled into fixed-pointconstants are given below:|||||||Length Range of signed values that can beassembledRange of unsigned values that can beassembled8 −2 63 to 2 63 −1 0 to 2 64 −14 −2 31 to 2 31 −1 0 to 2 32 −12 −2 15 to 2 15 −1 0 to 2 16 −11 −2 7 to 2 7 −1 0 to 2 8 −1The range of values depends on the implicitly or explicitly specified length (ifscaling is disregarded). If the value specified for a particular constant does not liewithin the allowable range for a given length, the constant is not assembled, butflagged as an error.A fixed-point constant is assembled as follows:1. The specified number, multiplied by any exponents, is converted to a binarynumber.2. Scaling is done, if specified. If a scale modifier is not provided, the fractionalportion of the number is lost.3. The binary value is rounded, if necessary. The resulting number does not differfrom the exact number specified by more than one in the least significant bitposition at the right.4. A negative number is carried in two’s-complement form.5. Duplication is applied after the constant has been assembled.The statement below generates 3 fullwords of data. The location attribute of CONWRDis the address of the first byte of the first word, and the length attribute is 4, theimplied length for a fullword fixed-point constant. The expression CONWRD+4 couldbe used to address the second constant (second word) in the field.CONWRD DC 3F’658474’Table 26. Fixed-point constantsSubfield Value Example Result1. Duplication factor Allowed2. Type F and H3. Type Extension D permitted withtype F4. Program type Allowed5. ModifiersImplicit length:(length modifiernot present)Alignment:(Length modifiernot present)Doubleword: 8 bytesFullword: 4 bytesHalfword: 2 bytesDoubleword,fullword orhalfwordChapter 5. Assembler instruction statements 147