Ch 3. Arithmetic for computers - (1)

1. Addition and Subtraction

Integer Addition

• two’s complement 가정
• Overflow가 발생하는 경우
  • magnitude가 너무 커져 숫자를 표현할 수 없을 때
  • Positive Operand + Positive Operand = Result(Sign = 1)
    • sign = 1(Negative)
  • Negative Operand + Negative Operand = Result(Sign = 0)
    • sign = 0(Positive or 0)

Integer Subtraction

• 7 - 6 = 7 + (-6)
• Overflow가 발생하는 경우
  • Positive Operand - Negative Operand = Result(Sign = 0)
    • sign = 0(Positive or 0)
  • Negative Operand - Positive Operand = Result(Sign = 1)
    • sign = 1(Negative)

Dealing with Overflow

1. Some languages (C)
   • overflow 무시
   • MIPS
     • addu, addiu, subu instructions
     • u(unsigned)
2. Other languages (Ada, Fortran..)
   • 프로그래머한테 에러 발생을 알림
   • invoke exception handler