sxtb

Signed Extend Byte (Thumb)

SXTB <Rd>, <Rm>

Sign-extends byte to word (Thumb).

Pseudocode Operation

Rd = SignExtend(Rm[7:0], 32)

Example

SXTB r0, r2

Encoding

Binary Layout

10110010

15:8

0

7

1

6

Rm

5:3

Rd

2:0

 

Format Thumb Data Proc

Opcode 0xB240

Extension T32 (Thumb)

Operands

• Rd
  Destination general-purpose register
• Rm
  Second source / offset general-purpose register

Related

Other forms of sxtb

• sxtb Signed Extend Byte (A32)
• sxtb Sign Extend Byte

Across architectures

Sign Extend Byte : how x86, ARM, RISC-V, and PowerISA each do this.

More in T32 (Thumb)

Reference

View in Arm A64 ISA Reference ↗ Arm AArch32 ISA

Instruction Forms

Encoding	Instruction		ISA		Bit pattern
0x06AF0070	SXTB{<c>}{<q>} {<Rd>,} <Rm> {, ROR #<amount>}		A32		cond | 01101 | 0 | 10 | 1111 | Rd | rotate | 0 | 0 | 0111 | Rm
0xB240	SXTB{<c>}{<q>} {<Rd>,} <Rm>		T32		10110010 | 0 | 1 | Rm | Rd
0xFA4FF080	SXTB{<c>}.W {<Rd>,} <Rm>		T32		111110100 | 10 | 0 | 1111 | 1111 | Rd | 1 | 0 | rotate | Rm

Description

Signed Extend Byte extracts an 8-bit value from a register, sign-extends it to 32 bits, and writes the result to the destination register. The instruction can specify a rotation by 0, 8, 16, or 24 bits before extracting the 8-bit value.

Operation

if ConditionPassed() then
    EncodingSpecificOperations();
    rotated = ROR(R[m], rotation);
    R[d] = SignExtend(rotated<7:0>, 32);