bfc

Bit Field Clear (Thumb)

BFC <Rd>, #<lsb>, #<width>

Clears a bitfield in a register.

Pseudocode Operation

msb ← lsb + width - 1
mask ← (1 << (msb + 1)) - (1 << lsb)
Rd ← Rd AND NOT mask

Example

BFC r0, #0, #width

Encoding

Binary Layout

11110

31:27

0

26

11

25:24

01

23:22

1

21

0

20

1111

19:16

0

15

imm3

14:12

Rd

11:8

imm2

7:6

0

5

msb

4:0

 

Format Thumb Bitfield

Opcode 0xF36F0000

Extension A32 (Base)

Operands

• Rd
  Destination general-purpose register
• lsb
  Start
• width
  Width

Related

Other forms of bfc

• bfc Bit Field Clear

More in A32 (Base)

Reference

View in Arm A64 ISA Reference ↗ Arm AArch32 ISA

Instruction Forms

Encoding	Instruction		ISA		Bit pattern
0x07C0001F	BFC{<c>}{<q>} <Rd>, #<lsb>, #<width>		A32		cond | 0111110 | msb | Rd | lsb | 001 | 1111
0xF36F0000	BFC{<c>}{<q>} <Rd>, #<lsb>, #<width>		T32		11110 | 0 | 11 | 01 | 1 | 0 | 1111 | 0 | imm3 | Rd | imm2 | 0 | msb

Description

Bit Field Clear clears any number of adjacent bits at any position in a register, without affecting the other bits in the register.

Operation

if ConditionPassed() then
    EncodingSpecificOperations();
    R[d]<msbit:lsbit> = Replicate('0', (msbit-lsbit)+1);
    // Other bits of R[d] are unchanged