dtstsfi

Decimal Test Significance Immediate

dtstsfi BF, U, FRB

Tests the significance of a decimal floating-point value in FPR[FRB] against an immediate value UIM.

Encoding

Binary Layout

0:5

6:10

11:15

16:20

FRB

21:30

675

Format X-form

Opcode 0xEC000546

Extension Decimal Floating-Point

Operands

BF
CR Field
U
Imm
FRB
Source
UIM
Immediate Reference Significance

Example

dtstsfi cr0, 0, f3

Registers Altered

CR, FPSCR

Reference

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

Description

The instruction compares the number of significant digits (NSDb) of the DFP value in FPR[FRB] with the reference significance specified by UIM. The result is placed into CR field BF and FPCC.

Operation

NSDb <- number of significant digits in FPR[FRB]
if UIM != 0 and UIM < NSDb then
    CR[BF] <- 0b0010
    FPCC <- 0b0010
else if UIM != 0 and UIM > NSDb or UIM = 0 then
    CR[BF] <- 0b0100
    FPCC <- 0b0100
else if UIM != 0 and UIM = NSDb then
    CR[BF] <- 0b1000
    FPCC <- 0b1000
else
    CR[BF] <- 0b0001
    FPCC <- 0b0001

Programming Note

The dtstsfi instruction is used to compare the number of significant digits in a DFP value with a specified reference significance. Ensure that the UIM (Upper Immediate) is correctly set according to the desired comparison. This instruction operates at the problem state and may raise exceptions if the FPR[FRB] contains an invalid DFP value. Performance can be optimized by minimizing the use of this instruction in critical loops due to its dependency on floating-point operations.