sub

Subtract

This instruction is defined by:

I, version >= 0

This instruction is included in the following profiles:

RVA20S64 (Mandatory)
RVA20U64 (Mandatory)
RVA22S64 (Mandatory)
RVA22U64 (Mandatory)

Encoding

Assembly format

sub rd, rs1, rs2

Synopsis

This instruction must have data-independent timing when extension Zkt is enabled.

Subtract the value in rs2 from rs1, and store the result in rd

Access

M	HS	U	VS	VU
Always	Always	Always	Always	Always

Always

Decode Variables

Bits<5> rs2 = $encoding[24:20];
Bits<5> rs1 = $encoding[19:15];
Bits<5> rd = $encoding[11:7];

Execution

IDL
Sail

XReg t0 = X[rs1];
XReg t1 = X[rs2];
X[rd] = t0 - t1;

{
  let rs1_val = X(rs1);
  let rs2_val = X(rs2);
  let result : xlenbits = match op {
    RISCV_ADD  => rs1_val + rs2_val,
    RISCV_SLT  => zero_extend(bool_to_bits(rs1_val <_s rs2_val)),
    RISCV_SLTU => zero_extend(bool_to_bits(rs1_val <_u rs2_val)),
    RISCV_AND  => rs1_val & rs2_val,
    RISCV_OR   => rs1_val | rs2_val,
    RISCV_XOR  => rs1_val ^ rs2_val,
    RISCV_SLL  => if   sizeof(xlen) == 32
                  then rs1_val << (rs2_val[4..0])
                  else rs1_val << (rs2_val[5..0]),
    RISCV_SRL  => if   sizeof(xlen) == 32
                  then rs1_val >> (rs2_val[4..0])
                  else rs1_val >> (rs2_val[5..0]),
    RISCV_SUB  => rs1_val - rs2_val,
    RISCV_SRA  => if   sizeof(xlen) == 32
                  then shift_right_arith32(rs1_val, rs2_val[4..0])
                  else shift_right_arith64(rs1_val, rs2_val[5..0])
  };
  X(rd) = result;
  RETIRE_SUCCESS
}