sext.b

Sign-extend byte

This instruction is defined by:

Encoding

svg

Synopsis

Sign-extends the least-significant byte in the source to XLEN by copying the most-significant bit in the byte (i.e., bit 7) to all of the more-significant bits.

Access

M

HS

U

VS

VU

Always

Always

Always

Always

Always

Decode Variables

Bits<5> rs1 = $encoding[19:15];
Bits<5> rd = $encoding[11:7];

Execution

  • Pruned, XLEN == 64

  • Original

if ((misa.B == 1'b0)) {
  raise(ExceptionCode::IllegalInstruction, mode(), $encoding);
}
X[rd] = {{56{X[rs1][7]}}, X[rs1][7:0]};
if (implemented?(ExtensionName::B) && (misa.B == 1'b0)) {
  raise(ExceptionCode::IllegalInstruction, mode(), $encoding);
}
if (xlen() == 32) {
  X[rd] = {{24{X[rs1][7]}}, X[rs1][7:0]};
} else if (xlen() == 64) {
  X[rd] = {{56{X[rs1][7]}}, X[rs1][7:0]};
}

Exceptions

This instruction may result in the following synchronous exceptions:

  • IllegalInstruction