dtstex

DFP Test Exponent X-form

dtstex BF,FRA,FRB

Compares the exponent values of two DFP operands and updates CR field BF and FPCC.

Encoding

Binary Layout

0

0:5

BF

6:8

FRA

9:10

FRB

11:15

162

16:31

 

Format X-form

Opcode 0xEC000144

Extension Decimal Floating-Point

Operands

• BF
  Condition Register Field
• FRA
  First Source DFP Floating-Point Register
• FRB
  Second Source DFP Floating-Point Register

Example

dtstex cr0, f2, f3

Registers Altered

CR field BF, FPSCR FPCC

Related

More in Decimal Floating-Point

Reference

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

Description

The exponent value (Ea) of the DFP operand in FRA is compared to the exponent value (Eb) of the DFP operand in FRB. The result of the compare is placed into CR field BF and the FPCC.

Operation

Ea ← exponent of DFP operand in FRA
Eb ← exponent of DFP operand in FRB
if (FRA is F) and (FRB is F) then
    if Ea < Eb then CR_BF || FPCC ← 0b1000
    else if Ea > Eb then CR_BF || FPCC ← 0b0100
    else CR_BF || FPCC ← 0b0010
else if (FRA is ∞) and (FRB is ∞) then CR_BF || FPCC ← 0b0010
else if (FRA is QNaN or SNaN) and (FRB is QNaN or SNaN) then CR_BF || FPCC ← 0b0010
else CR_BF || FPCC ← 0b0001

Programming Note

The dtstex instruction compares the exponents of two DFP operands and sets the condition register field BF and floating-point status and control register (FPSCR) FPCC based on the comparison. Ensure that both operands are properly aligned and valid; otherwise, the instruction may raise exceptions. This instruction is useful for sorting or filtering operations where exponent values need to be compared.