sub

Subtract

This instruction is defined by:

  • I, version >= I@2.1.0

This instruction is included in the following profiles:

  • MockProfile 64-bit S-mode (Mandatory)

  • MockProfile 64-bit Unpriv (Mandatory)

  • RVA20S64 (Mandatory)

  • RVA20U64 (Mandatory)

  • RVA22S64 (Mandatory)

  • RVA22U64 (Mandatory)

  • RVA23S64 (Mandatory)

  • RVA23U64 (Mandatory)

  • RVB23S64 (Mandatory)

  • RVB23U64 (Mandatory)

  • RVI20U32 (Mandatory)

  • RVI20U64 (Mandatory)

Encoding

svg

Assembly format

sub rd, rs1, rs2

Synopsis

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

Subtract the value in xs2 from xs1, and store the result in xd

Access

M HS U VS VU

Always

Always

Always

Always

Always

Decode Variables

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

Execution

  • IDL

  • Sail

XReg t0 = X[xs1];
XReg t1 = X[xs2];
X[xd] = t0 - t1;
{
  let xs1_val = X(xs1);
  let xs2_val = X(xs2);
  let result : xlenbits = match op {
    RISCV_ADD  => xs1_val + xs2_val,
    RISCV_SLT  => zero_extend(bool_to_bits(xs1_val <_s xs2_val)),
    RISCV_SLTU => zero_extend(bool_to_bits(xs1_val <_u xs2_val)),
    RISCV_AND  => xs1_val & xs2_val,
    RISCV_OR   => xs1_val | xs2_val,
    RISCV_XOR  => xs1_val ^ xs2_val,
    RISCV_SLL  => if   sizeof(xlen) == 32
                  then xs1_val << (xs2_val[4..0])
                  else xs1_val << (xs2_val[5..0]),
    RISCV_SRL  => if   sizeof(xlen) == 32
                  then xs1_val >> (xs2_val[4..0])
                  else xs1_val >> (xs2_val[5..0]),
    RISCV_SUB  => xs1_val - xs2_val,
    RISCV_SRA  => if   sizeof(xlen) == 32
                  then shift_right_arith32(xs1_val, xs2_val[4..0])
                  else shift_right_arith64(xs1_val, xs2_val[5..0])
  };
  X(xd) = result;
  RETIRE_SUCCESS
}