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AIX Version 4.3 Assembler Language Reference

rac (Real Address Compute) Instruction


Translates an effective address into a real address and stores the result in a general-purpose register.

Note: The rac instruction is supported only in the POWER architecture.


rac RT,RA,RB
rac. RT,RA,RB


The rac instruction computes an effective address (EA) from the sum of the contents of general-purpose register (GPR) RA and the contents of GPR RB, and expands the EA into a virtual address.

If RA is not 0 and if RA is not RT, then the rac instruction stores the EA in GPR RA, translates the result into a real address, and stores the real address in GPR RT.

Consider the following when using the rac instruction:

The rac instruction has two syntax forms. Each syntax form has a different effect on Condition Register Field 0.

Syntax Form Overflow Exception (OE) Fixed-Point Exception Register Record Bit (Rc) Condition Register Field 0
rac None None 0 None
rac None None 1 EQ,SO

The two syntax forms of the rac instruction do not affect the Fixed-Point Exception Register. If the syntax form sets the Record (Rc) bit to 1, the instruction effects the Equal (EQ) and Summary Overflow (SO) bit in Condition Register Field 0.

Note: The hardware may first search the Translation Look-Aside buffer for the address. If this fails, the Page Frame table must be searched. In this case, it is not necessary to load a Translation Look-Aside buffer entry.


RT Specifies the target general-purpose register where result of operation is stored.
RA Specifies the source general-purpose register for EA calculation.
RB Specifies the source general-purpose register for EA calculation.


The rac instruction instruction is privileged.

Related Information

Processing and Storage

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