1. Lecture 05: Assembly Language Programming (2)

2. The 80x86 IBM PC and Compatible Computers Chapter 3 Arithmetic & Logic Instructions and Programs Chapter 6 Signed Numbers, Strings, and Tables

3. Arithmetic Instructions zAddition zSubtraction zMultiplication zDivision

4. Unsigned Addition zADD dest, src ;dest = dest + src yDest can be a register or in memory ySrc can be a register, in memory or an immediate yNo mem-to-mem operations in 80X86 yChange ZF, SF, AF, CF, OF, PF zADC dest, src ;dest = dest + src +CF yFor multi-byte numbers yIf there is a carry from last addition, adds 1 to the result

5. Addition Example of Individual Bytes Draw the layout of the data segment in memory What’s this for?

6. Addition Example of Multi-byte Nums

7. Unsigned Subtraction zSUB dest, src ;dest = dest - src yDest can be a register or in memory ySrc can be a register, in memory or an immediate yNo mem-to-mem operations in 80X86 yChange ZF, SF, AF, CF, OF, PF zSBB dest, src ;dest = dest - src – CF yFor multi-byte numbers yIf there is a borrow from last subtraction, subtracts 1 from the result

8. Subtraction Example of Individual Bytes zCPU carries out 1.take the 2’s complement of the src 2.add it to the dest 3.invert the carry After these three steps, if zCF = 0: positive result; zCF = 1: negative result, left in 2’s complement yMagnitude: NOT + INC (if a programmer wants the magnitude)

9. Subtraction Example of Multi-byte Nums

10. Unsigned Multiplication zMUL operand zbyte X byte: yOne implicit operand is AL, the other is the operand, result is stored in AX zword X word: yOne implicit operand is AX, the other is the operand, result is stored in DX & AX zword X byte: yAL hold the byte, AH = 0, the word is the operand, result is stored in DX & AX;

11. Unsigned Multiplication Example

12. Unsigned Division zDIV denominator yDenominator cannot be zero yQuotient cannot be too large for the assigned register zbyte / byte: yNumerator in AL, clear AH; quotient is in AL, remainder in AH zword / word: yNumerator in AX, clear DX; ; quotient is in AX, remainder in DX zword / byte: yNumerator in AX; quotient is in AL (max 0FFH), remainder in AH zdouble-word / word: yNumerator in DX, AX; quotient is in AX (max 0FFFFH), remainder in DX yDenominator can be in a register or in memory

13. Unsigned Division Example

14. Logic Instructions zAND zOR zXOR zNOT zLogical SHIFT zROTATE zCOMPARE

15. AND zAND dest, src yBit-wise logic ydest can be a register or in memory; src can be a register, in memory, or immediate

16. OR zOR dest, src yBit-wise logic ydest can be a register or in memory; src can be a register, in memory, or immediate

17. XOR zXOR dest, src yBit-wise logic ydest can be a register or in memory; src can be a register, in memory, or immediate

18. NOT zNOT operand yBit-wise logic yOperand can be a register or in memory XNOT X ------------------------------------------- 1 0 0 1

19. Logical SHIFT zSHR dest, times ydest can be a register or in memory y0->MSB->…->LSB->CF yTimes = 1: SHR xx, 1 yTimes >1: MOV CL, times SHR xx, CL zSHL dest, times yAll the same except in reverse direction

20. Example: BCD & ASCII Numbers Conversion zBCD: Binary Coded Decimal yDigits 0~9 in binary representation yUnpacked, packed zASCII yCode for all characters that you can read or write yDigit characters ‘0’~’9’

21. ASCII -> Unpacked BCD Conversion zSimply remove the higher 4 bits “0011” zE.g., asc DB ‘3’ unpackDB ? ------------------------- MOV AH, asc AND AH, 0Fh MOV unpack, AH

22. ASCII -> Packed BCD Conversion zFirst convert ASCII to unpacked BCD zThen, combine two unpacked into one packed  E.g., asc DB ‘23’ unpackDB ? ------------------------- MOV AH, asc MOV AL, asc+1 AND AX, 0F0Fh MOV CL, 4 SHL AH, CL OR AH, AL MOV unpack, AH

23. ROTATE zROR dest, times ydest can be a register, in memory yTimes = 1: ROR xx, 1 yTimes >1: MOV CL, times ROR xx, CL zROL dest, times yAll the same except in reverse direction

24. ROTATE Cont. zRCR dest, times ydest can be a register, in memory yTimes = 1: RCR xx, 1 yTimes >1: MCV CL, times RCR xx, CL zRCL dest, times yAll the same except in reverse direction

25. COMPARE of Unsigned Numbers zCMP dest, src yFlags affected as (dest – src) but operands remain unchanged  E.g., CMP AL, 23 JA lable1 ; jump if above, CF = ZF = 0

27. COMPARE of Signed Numbers zCMP dest, src y Same instruction as the unsigned case y but different understanding about the numbers and therefore different flags checked

29. Quiz Given the ASCII table, write an algorithm to convert lowercase letters in a string into uppercase letters and implement your algorithm using 86 assembly language.

30. Answer to Quiz

31. XLAT Instruction & Look-up Tables zSelf-learning ypp. 189 in Chapter 6