mtfsfi

Move To FPSCR Field Immediate

mtfsfi BF, U

Writes a 4-bit immediate to a specific FPSCR field.

Encoding

Binary Layout

63

0:5

BF

6:10

/

11:15

U

16:20

134

21:30

/

31

 

Format X-form

Opcode 0xFC00010C

Extension Floating-Point

Operands

• BF
  Field Index
• U
  Immediate

Example

mtfsfi cr0, 0

Registers Altered

FPSCR

Related

More in Floating-Point

Reference

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

Description

Writes a 4-bit immediate value U into a 4-bit field of the FPSCR selected by BF. The target FPSCR field is at bits [4×BF : 4×BF+3]. This instruction directly modifies FPSCR state and may affect subsequent floating-point operations.

Operation

FPSCR[4*BF : 4*BF+3] ← U

Programming Note

Use mtfsfi to directly manipulate specific fields in the FPSCR, such as enabling or disabling exceptions. Ensure the immediate value fits within the specified field size to avoid undefined behavior. This instruction operates at user privilege level and does not generate exceptions for valid immediate values.