ftsqrt

Float Test for Square Root

ftsqrt BF, FRB

Tests for conditions that would cause a sqrt exception.

Encoding

Binary Layout

63

0:5

BF

6:8

/

9:10

0

11:15

FRB

16:20

160

21:30

/

31

 

Format X-form

Opcode 0xFC000140

Extension Floating-Point

Operands

• BF
  CR Field
• FRB
  Source

Example

ftsqrt cr0, f3

Registers Altered

FPSCR

Related

More in Floating-Point

Reference

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

Description

Tests the floating-point value in FRB to determine if it would cause an exception when used as the operand to a square root instruction, setting the condition bits in CR field BF accordingly. The result encodes whether the operand is negative, zero, positive, or a special value (NaN, infinity). No floating-point result is produced and FPSCR is not modified.

Operation

if FRB < 0.0 then
  CR[BF] ← 0b1000
else if FRB = 0.0 then
  CR[BF] ← 0b0100
else if FRB > 0.0 then
  CR[BF] ← 0b0010
else
  CR[BF] ← 0b0001

Programming Note

The ftsqrt instruction is useful for checking special conditions of a floating-point number before performing square root operations. It sets the FE flag if the operand is zero, NaN, infinity, negative, or has an exponent less than or equal to -970. The FG flag is set if the operand is zero, infinity, or denormalized. Ensure the operand is properly aligned and in double-precision format to avoid unexpected results.