sxtb

Signed Extend Byte (Thumb)

SXTB <Rd>, <Rm>

Sign-extends byte to word (Thumb).

Details

Sign-extends an 8-bit byte value to a 32-bit word in the T32 (Thumb) instruction set. The least-significant byte of Rm is sign-extended and written to Rd. No condition flags are affected.

Pseudocode Operation

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

Example

SXTB r0, r2

Encoding

Binary Layout
10110010
0
1
Rm
Rd
 
Format Thumb Data Proc
Opcode 0xB240
Extension T32 (Thumb)

Operands

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

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);