HLASM: V1R6 Language Ref

USING instructionIf the dependent USING instruction specifies a supporting base address that iswithin the range of more than one ordinary USING, the assembler determineswhich base register to use during base-displacement resolution as follows:v The assembler computes displacements from the ordinary USING base addressthat gives the smallest displacement, and uses the corresponding base register.v If more than one ordinary USING gives the smallest displacement, the assembleruses the higher-numbered register for assembling addresses within thecoinciding USING ranges.Domain of a dependent USING instructionThe domain of a dependent USING instruction (called the dependent USINGdomain) begins where the dependent USING appears in the source module andcontinues until the end of the source module, except when:v You end the domain of the corresponding ordinary USING by specifying thebase register or registers from the ordinary USING instruction in a subsequentDROP instruction.v You end the domain of the corresponding ordinary USING by specifying thesame base register or registers from the ordinary USING instruction in asubsequent ordinary USING instruction.v You end the domain of a labeled dependent USING by specifying the label ofthe labeled dependent USING in the operand of a subsequent DROP instruction.v You end the domain of a labeled dependent USING by specifying the label ofthe labeled dependent USING in the operand of a subsequent labeled USINGinstruction.When a labeled dependent USING domain is dropped, none of any subordinateUSING domains are dropped. In the following example the labeled dependentUSING BLBL1 is not dropped, even though it appears to be dependent on theUSING ALBL2 that is being dropped:ALBL1 USING DSECTA,14USINGDSECTB,ALBL1.A..ALBL2 USING DSECTA,ALBL1.A.BLBL1 USING DSECTA,ALBL2.A.DROPALBL2.DSECTA DSECTA DS ADSECTB DSECTB DS AA dependent USING is not dependent on another dependent USING. It isdependent on the ordinary or labeled USING that is finally used to resolve theaddress. For example, the USING at BLBL1 is dependent on the ALBL1 USING.Remember that all dependent USINGs must eventually be based on an ordinary orlabeled USING that provides the base register used for base-displacementresolutions.226 HLASM: V1R6 Language Ref