max

Maximum

This instruction is defined by:

anyOf:
- B, version >= 0
- Zbb, version >= 0

This instruction is included in the following profiles:

RVA22S64 (Mandatory)
RVA22U64 (Mandatory)

Encoding

Assembly format

max rd, rs1, rs2

Synopsis

This instruction returns the larger of two signed integers.

Software Hint

Calculating the absolute value of a signed integer can be performed using the following sequence: neg rD,rS followed by `max rD,rS,rD. When using this common sequence, it is suggested that they are scheduled with no intervening instructions so that implementations that are so optimized can fuse them together.

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

if (implemented?(ExtensionName::B) && (CSR[misa].B == 1'b0)) {
  raise(ExceptionCode::IllegalInstruction, mode(), $encoding);
}
X[rd] = ($signed(X[rs1]) > $signed(X[rs2])) ? X[rs1] : X[rs2];

{
  let rs1_val = X(rs1);
  let rs2_val = X(rs2);
  let result : xlenbits = match op {
    RISCV_ANDN => rs1_val & ~(rs2_val),
    RISCV_ORN  => rs1_val | ~(rs2_val),
    RISCV_XNOR => ~(rs1_val ^ rs2_val),
    RISCV_MAX  => to_bits(sizeof(xlen), max(signed(rs1_val),   signed(rs2_val))),
    RISCV_MAXU => to_bits(sizeof(xlen), max(unsigned(rs1_val), unsigned(rs2_val))),
    RISCV_MIN  => to_bits(sizeof(xlen), min(signed(rs1_val),   signed(rs2_val))),
    RISCV_MINU => to_bits(sizeof(xlen), min(unsigned(rs1_val), unsigned(rs2_val))),
    RISCV_ROL  => if sizeof(xlen) == 32
                  then rs1_val <<< rs2_val[4..0]
                  else rs1_val <<< rs2_val[5..0],
    RISCV_ROR  => if sizeof(xlen) == 32
                  then rs1_val >>> rs2_val[4..0]
                  else rs1_val >>> rs2_val[5..0]
  };
  X(rd) = result;
  RETIRE_SUCCESS
}

Exceptions

This instruction may result in the following synchronous exceptions:

IllegalInstruction