bclr
Single-Bit clear (Register)
This instruction is defined by:
-
anyOf:
-
B, version >= B@1.0.0
-
Zbs, version >= Zbs@1.0.0
-
This instruction is included in the following profiles:
-
RVA22U64 (Mandatory)
-
RVA23U64 (Mandatory)
-
RVB23U64 (Mandatory)
Synopsis
This instruction returns rs1 with a single bit cleared at the index specified in rs2. The index is read from the lower log2(XLEN) bits of rs2.
Decode Variables
Bits<5> rs2 = $encoding[24:20];
Bits<5> rs1 = $encoding[19:15];
Bits<5> rd = $encoding[11:7];idl
Execution
-
IDL
-
Sail
if (implemented?(ExtensionName::B) && (CSR[misa].B == 1'b0)) {
raise(ExceptionCode::IllegalInstruction, mode(), $encoding);
}
XReg index = X[rs2] & (xlen() - 1);
X[rd] = X[rs1] & ~(1 << index);idl
{
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
}sail