neg

Negate

neg RT, RA

Computes the two's complement negation of a register (0 - RT).

Encoding

Binary Layout

0:5

6:10

11:15

00000

16:20

104

22:30

Format XO-form

Opcode 0x7C0000D0

Extension Base

Operands

RT
Target Register
RA
Source Register

Example

neg r3, r4

// r3 = -r4

Registers Altered

CR0

Reference

View in PowerISA v3.1C Specification ↗ OPF Power ISA v3.1C

Description

Computes the two's complement negation (0 - RA) of the source register and stores the result in RT. If OE=1, sets OV and SO in XER on signed overflow (when RA=0x8000_0000_0000_0000). When Rc=1, updates CR0 based on the result.

Operation

result ← -(RA)
RT ← result
if OE = 1 then
  if RA = 0x8000_0000_0000_0000 then
    XER[OV] ← 1; XER[SO] ← 1
  else
    XER[OV] ← 0
if Rc = 1 then
  CR0 ← record_result(result)

Programming Note

When Rc=1 (dot form), CR0 is updated with the signed comparison of the result against zero (LT, GT, EQ) and the current SO bit from XER.

neg