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Peter Flass (talk | contribs) |
→Assembler instructions: relative addresses; DROP |
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USING base,reg-1,...,reg-n
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Machine instruction addresses on S/360 specify a ''displacement'' (0–4095 bytes) from the value in a ''base register''; While later versions of the architecture added relative-address formats, the older formats are still used by many instructions. <code>USING</code> allows the programmer to tell the assembler that the specified base registers are assumed to contain the address of "base", base+4096 (if multiple registers are specified), etc. This only provides a shortcut for the programmer, who otherwise would have to specify the base register in each instruction. Programmers are still responsible for actually loading the address of "base" into the register before writing code that depends on this value.
The related <code>DROP</code> assembler instruction nullifies a previous <code>USING</code>.
===Machine instructions (mnemonic)===
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