sign_extend_imm13
return (fetch_reg(rs1, regs) + sign_extend_imm13(insn));
return (safe_fetch_reg(rs1, regs) + sign_extend_imm13(insn));
addr = (fetch_reg(rs1, regs) + sign_extend_imm13(insn));
value = sign_extend_imm13(insn);