bext

Single-Bit extract (Register)

Returns a single bit extracted from xs1 at the index specified in xs2. The index is read from the lower log2(XLEN) bits of xs2.

Assembly format

bext rd, rs1, rs2

Decode Variables

Bits<5> xs2 = $encoding[24:20];
Bits<5> xs1 = $encoding[19:15];
Bits<5> xd = $encoding[11:7];

Execution

  • IDL

  • Sail

if (implemented?(ExtensionName::B) && (misa.B == 1'b0)) {
  raise(ExceptionCode::IllegalInstruction, mode(), $encoding);
}
XReg index = X[xs2] & (xlen() - 1);
X[xd] = (X[xs1] >> index) & 1;
{
  let rs1_val = X(rs1);
  let rs2_val = X(rs2);
  let mask : xlenbits = if sizeof(xlen) == 32
                        then zero_extend(0b1) << rs2_val[4..0]
                        else zero_extend(0b1) << rs2_val[5..0];
  let result : xlenbits = match op {
    RISCV_BCLR => rs1_val & ~(mask),
    RISCV_BEXT => zero_extend(bool_to_bits((rs1_val & mask) != zeros())),
    RISCV_BINV => rs1_val ^ mask,
    RISCV_BSET => rs1_val | mask
  };
  X(rd) = result;
  RETIRE_SUCCESS
}

Exceptions

This instruction may result in the following synchronous exceptions:

  • IllegalInstruction

Encoding

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Defining extension

Zbs, version >= Zbs@1.0.0

Access

M

Always

Containing profiles

  • Mandatory: RVA22S64, RVA22U64, RVA23M64, RVA23S64, RVA23U64, RVB23M64, RVB23S64, RVB23U64

  • Optional: