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BITWISE operations

BITWISE operations. 353156 – Microprocessor Asst. Prof. Dr. Choopan Rattanapoka and Asst. Prof. Dr. Suphot Chunwiphat. Objectives. To understand Bitwise Logical Operations OR AND XOR Shift Operations Shift Left Shift Right Rotate. Bitwise Operations (1). Up until now, we’ve done :

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BITWISE operations

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  1. BITWISE operations 353156 – Microprocessor Asst. Prof. Dr. ChoopanRattanapoka and Asst. Prof. Dr. SuphotChunwiphat

  2. Objectives • To understand • Bitwise Logical Operations • OR • AND • XOR • Shift Operations • Shift Left • Shift Right • Rotate

  3. Bitwise Operations (1) • Up until now, we’ve done : • Arithmetic (ADD, SUB, RSB, ..etc..) • Some of data movement (MOV) • All of these instructions view content of register as a single quantity • But for bitwise operations, we will see the content of register as 32 bits rather than as a single 32-bit number

  4. Bitwise Operations (2) • Since register are composed of 32 bits, we may want to access individual bits rather than the whole. • Introduction two new classes of instructions/operations : • Logical Instruction • Shift Operations

  5. Logical Operations • Operator Names: • AND • BIC • ORR • EOR • Operands • Destination : Register • Operand1 : Register • Operand2 : Register, Shifted Register, Immediate • Example • AND a1, v1, v2 • AND a1, v1, #0x40

  6. Logical AND Operator • AND (truth table) • AND : bit-by-bit operation leaves a 1 in the result only if both bits of the operands are 1

  7. Example : Logical AND Operator • Assume that register A and B are 8-bit register • Let A stores value 0011 1011 • Let B stores value 1001 0010 • Find A AND B 0 0 1 1 1 0 1 1 AND 1 0 0 1 0 0 1 0 0 0 0 1 0 0 1 0

  8. Exercise 1: Logical AND Operator • What is the value store in register R0 after the execution of program is done (1) (2) AREA ex1_1, CODE, READONLY ENTRY start MOV a2, #0x42 MOV a3, #0xFC AND a1, a2, a3 END AREA ex1_2, CODE, READONLY ENTRY start MOV a2, #0xBC000000 AND a1, a2, #0xFF END

  9. Logical BIC (AND NOT) Operator • BIC (BIt Clean) : bit-by-bit operation leaves a 1 in the result only if bit of the first operand is 1 and the second operands 0 • Example 0 0 1 1 BIC 0 1 0 1 0 0 1 0

  10. Exercise 2: Logical BIC Operator • What is the value store in register R0 after the execution of program is done (1) (2) AREA ex2_1, CODE, READONLY ENTRY start MOV a2, #0x42 MOV a3, #0xFC BIC a1, a2, a3 END AREA ex2_2, CODE, READONLY ENTRY start MOV a2, #0xBC000000 BIC a1, a2, #0xFF END

  11. MASK • AND and BIC normally use to create a mask • Example : Given R0 stores 0x12345678 • if we want to keep only the value of the last 2 bytes and we want to clear the first 2 bytes to 0 (0x00005678) • R1 stores 0xFFFF • AND R0, R0, R1 ; short written constant value • if we want to keep only the value of the first 2 bytes and we want to clear the last 2 bytes to 0 (0x12340000) • R1 stores 0xFFFF0000 • AND R0, R0, R1 ; long written constant value • R2 stores 0xFFFF • BIC R0, R0, R2 ; better ?

  12. Logical OR Operator • OR (truth table) • OR : bit-by-bit operation leaves a 1 in the result if either bit of the operands is 1

  13. Example : Logical OR Operator • Assume that register A and B are 8-bit register • Let A = 0011 1011, and B = 1001 0010 • Find A OR B 0 0 1 1 1 0 1 1 OR 1 0 0 1 0 0 1 0 • Example : ARM Instruction • ORR R0, R0, #0x20 1 0 1 1 1 0 1 1

  14. Exercise 3 : Logical OR Operator • What is the value store in register R0 after the execution of program is done AREA ex3_1, CODE, READONLY ENTRY start MOV a2, #0x34 MOV a3, #0x86 ORR a1, a2, a3 END

  15. Logical XOR Operator • XOR (truth table) • XOR : bit-by-bit operation leaves a 1 in the result if bit of the operands are different

  16. Example : Logical XOR Operator • Assume that register A and B are 8-bit register • Let A = 0011 1011, and B = 1001 0010 • Find A XOR B 0 0 1 1 1 0 1 1 XOR 1 0 0 1 0 0 1 0 • Example : ARM Instruction • EOR R0, R0, #0x20 1 0 1 0 1 0 0 1

  17. Exercise 4 : Logical XOR Operator • What is the value store in register R0 after the execution of program is done AREA ex4_1, CODE, READONLY ENTRY start MOV a2, #0x34 MOV a3, #0x86 EOR a1, a2, a3 END

  18. Shift Operations • Shift means move all the bits in a word to the left or right by number of bits • In ARM, there are 3 types of shift operations • Fill emptied bits with 0s (LSL, LSR) • Fill emptied bits with sign bits (ASR) • Fill emptied bits with the bits falling (rotation) (ROR)

  19. Shift Operations (Type 1) • Move all the bits in a word to the left or right by a number of bits, filling the emptied bits with 0s • Example : Given A an 8-bit register which stores data 1100 1010 1 1 0 0 1 0 1 0 0 0 0 0 1 1 0 0 1 0 1 0 Shift right by 4 bits Shift left by 4 bits 1 1 0 0 1 0 1 0 0 0 0 0

  20. LSL, LSR Instructions • In ARM, we have 2 instructions for shift operation type 1 • LSL (Logical Shift Left) • LSR (Logical Shift Right) • We can use 2 formats of instruction • Opcodedest_reg, reg_contains_number_of_bit_to_shift • LSL R0, R1 ; R1 must store number of bit to shift • Opcodedest_reg, src_reg, constant_number_of_bit_to_shift • LSR R0, R1, #4 ; Shift right value in R1 for 4 bits and then store it to R0 • ** Only R0-R7 can do Shift operations **

  21. Exercise 5: LSL, LSR Operations • What is the value store in register R0 after the execution of program is done (1) (2) AREA ex5_1, CODE, READONLY ENTRY start MOV a1, #0x01 MOV a2, #4 LSL a1, a2 END AREA ex5_2, CODE, READONLY ENTRY start MOV a1, #0xFF LSR a1, a1, #0x4 END

  22. Shift Operations (Type 2) • Move all the bits in a word to the right by a number of bits, filling the emptied bits with sign bits • Example : • Given A an 8-bit register which stores data 1100 1010 • Given A an 8-bit register which stores data 0100 1010 1 1 0 0 1 0 1 0 1 1 1 1 1 1 0 0 1 0 1 0 Shift right by 4 bits 0 1 0 0 1 0 1 0 0 0 0 0 1 1 0 0 1 0 1 0 Shift right by 4 bits

  23. ASR Instructions • ASR (ArithmaticShift Right) • We can use 2 formats of instruction • Opcodedest_reg, reg_contains_number_of_bit_to_shift • ASR R0, R1 ; R1 must store number of bit to shift • Opcodedest_reg, src_reg, constant_number_of_bit_to_shift • ASR R0, R1, #4 ; Shift right value in R1 for 4 bits and then store it to R0 • ** Only R0-R7 can do Shift operations **

  24. Exercise 6: ASR Operations • What is the value store in register R0 after the execution of program is done (1) (2) AREA ex6_1, CODE, READONLY ENTRY start MOV a1, #0xFFFFFF10 MOV a2, #2 ASR a1, a2 END AREA ex6_2, CODE, READONLY ENTRY start MOV a1, #0xFF ASR a1, a1, #0x2 END

  25. Shift Operations (Type 3) • Move all the bits in a word to the right by a number of bits, filling the emptied bits with the bits falling of the right • Example : Given A an 8-bit register which stores data 1100 1010 Rotate right by 3 bits 1 0 1 1 0 1 0 0 1 0 0 1 1 0 0 1 0 0 1 1 0 1 1 0 0 1 0

  26. ROR Instructions • ROR (ROtateRight) • We can use 2 formats of instruction • Opcodedest_reg, reg_contains_number_of_bit_to_shift • ROR R0, R1 ; R1 must store number of bit to shift • Opcodedest_reg, src_reg, constant_number_of_bit_to_shift • ROR R0, R1, #4 ; Rorate right value in R1 for 4 bits and then store it to R0 • ** Only R0-R7 can do Shift operations **

  27. Exercise 7: ROR Operations • What is the value store in register R0 after the execution of program is done (1) (2) AREA ex7_1, CODE, READONLY ENTRY start MOV a1, #0xFFFFFF10 MOV a2, #4 ROR a1, a2 END AREA ex7_2, CODE, READONLY ENTRY start MOV a1, #0xFF ROR a1, a1, #0x4 END

  28. Review : 2nd Operand • 2ndoperand for operation : • register • immediate(numerical constant) • shifted register • Example : • MOV R0, R1 • MOV R0, #0x12 • MOV R0, R1, LSL #4 ; R0  (R1 << 4)

  29. Barrel Shifter : The Second Operand • Register, optionally with shift operation applied • Shift value can be either : • 5 bit unsigned integer • ADD R0, R1, R2, LSL #8 ;R0  R1 + (R2 << 8 bits) • Specified in bottom of another register • ADD R0, R1, R2, LSL R3 ;R0  R1 + (R2 << R3 bits) Operand 1 Operand 2 Barrel Shifter • Immediate value • 8 bit number • Can be rotated right through as even number of position • Assembler will calculate rotate for you from constant • ADD R0, R1, #10 ; R0  R1 + 10 • ADD R0, R1, #0xFF00 ; R0  R1 + (0xFF << 16 bits) • ADD R0, R1, #0xFFF ; ERROR ALU Result

  30. Assignment 5 • What is the value store in register R0 after the execution of program is done (explain the result of each instruction) (1) (2) AREA hw5_1, CODE, READONLY ENTRY start MOV a1, #0xFFFFFF18 MOV a2, #16 ROR a1, a2 MOV a2, #0xFF000000 AND a1, a1, a2, LSR #4 LSR a1, #16 END AREA hw5_2, CODE, READONLY ENTRY start MOV a1, #0xFF MOV a2, #0xCC MOV a3, #16 ADD a1, a1, a2, LSL a3 EOR a2, a2, #0x65 ORR a1, a1, a2, LSL #8 END

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