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AIX Version 4.3 Assembler Language Reference

abs (Absolute) Instruction

Purpose

Takes the absolute value of the contents of a general-purpose register and places the result in another general-purpose register.

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

Syntax

POWER
abs RT,RA
abs. RT,RA
abso RT,RA
abso. RT,RA

Description

The abs instruction places the absolute value of the contents of general-purpose register (GPR) RA into the target GPR RT.

If GPR RA contains the most negative number ('8000 0000'), the result of the instruction is the most negative number, and the instruction will set the Overflow bit in the Fixed-Point Exception Register to 1 if the OE bit is set to 1.

The abs instruction has four syntax forms. Each syntax form has a different effect on Condition Register Field 0 and the Fixed-Point Exception Register.

Syntax Form Overflow Exception (OE) Fixed-Point Exception Register Record Bit (Rc) Condition Register Field 0
abs 0 None 0 None
abs. 0 None 1 LT,GT,EQ,SO
abso 1 SO,OV 0 None
abso. 1 SO,OV 1 LT,GT,EQ,SO

The four syntax forms of the abs instruction always affect the Carry bit (CA) in the Fixed-Point Exception Register. If the syntax form sets the Overflow Exception (OE) bit to 1, the instruction affects the Summary Overflow (SO) and Overflow (OV) bits in the Fixed-Point Exception Register. If the syntax form sets the Record (Rc) bit to 1, the instruction affects the Less Than (LT) zero, Greater Than (GT) zero, Equal To (EQ) zero, and Summary Overflow (SO) bits in Condition Register Field 0.

Parameters

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

Examples

  1. The following code takes the absolute value of the contents of GPR 4 and stores the result in GPR 6: 
    # Assume GPR 4 contains 0x7000 3000.
abs 6,4
# GPR 6 now contains 0x7000 3000.
  2. The following code takes the absolute value of the contents of GPR 4, stores the result in GPR 6, and sets Condition Register Field 0 to reflect the result of the operation: 
    # Assume GPR 4 contains 0xFFFF FFFF.
abs. 6,4
# GPR 6 now contains 0x0000 0001.
  3. The following code takes the absolute value of the contents of GPR 4, stores the result in GPR 6, and sets the Summary Overflow and Overflow bits in the Fixed-Point Exception Register to reflect the result of the operation: 
    # Assume GPR 4 contains 0xB004 3000.
abso 6,4
# GPR 6 now contains 0x4FFB D000.
  4. The following code takes the absolute value of the contents of GPR 4, stores the result in GPR 6, and sets the Summary Overflow and Overflow bits in the Fixed-Point Exception Register and Condition Register Field 0 to reflect the result of the operation: 
    # Assume GPR 4 contains 0x8000 0000.
abso. 6,4
# GPR 6 now contains 0x8000 0000.

Related Information

Fixed-Point Processor.

Fixed-Point Arithmetic Instructions.

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