3/21/2009. Lecture 15: Data Structure & Parameter Passing. Define Constants with EQU. Define Variables with DC and DS. Define Variables with DC and DS

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1 Define Constants with EQU Lecture 15: Data Structure & arameter assing v The EQU directive is exactly like having a #define in C. It allows the programmer to specify a string that will take the place of the given label at compile time. v Syntax of EQU: <Label> EQU <Expression> Textbook: The Microprocessor: Hardware and Software rinciples and pplications, by James ntonakos, 5th Edition, rentice Hall, Excerpted from lecture notes prepared by Jie Hu, ssistant rofessor, Electrical and Computer Engineering Newark College of Engineering New Jersey Institute of Technology v This directive simply allows you to make a name equivalent to its value (i.e., it's a form of short hand). <Label>=<Expression> v Examples: XVL EQU 7 MOVE.#XVL, D0 equivalent to MOVE.#7, D0 v The define constant (DC) directive allows you to put a data value in memory at the time when the program is first loaded. v The DC directive takes the suffix.,.w, or.l. v Several values can be put on one line (each value is separated by a comma). v Syntax of DC: [Label] DC.{,W,L} exp [, exp2 [, exp3 []]] v Different from EQU, DC directive actually sets aside memory and sets the value of that memory to the (compile time) value of the given expression. v The define storage (DS) directive allows programmer to allocate or reserve memory space for a number of bytes/words/longwords that is uninitialized. v This directive is supposed to actually let you define storage that you can use to store global variables. v Syntax of DS [Label] DS.{,W,L} <Value> reserved memory space = <size> <value> v The optional label field gives the address of the first location in memory allocated to the DC constants. v Examples of DC: ORG $ C DC DEF DC E8 GHI DC.W D690 JKL DC.L MOVE. C, D0 ;read from memory location $8400 MOVE. D0, C ;write to memory location $8400 v Examples of DS: COUNT DS. 1 SIZE DS.W 1 LENGTH DS.L 1 One-Dimension rrays v n array is a data structure that consists of a fixed number of elements of the same data size occupies a continuous region of the memory space v Use DC to define an array with element value initialized CRDS DC. 0,0,0,0,0 SUITS DC.W 0,0,0,0,0 RRY DC.W 8, 9, 7, $5 v Use DS to define an array without initial value CRDS DS. 5 SUITS DS.W 5 LONGS DS.L 7 1

2 ccessing One-Dimension rrays ccessing One-Dimension rrays v Given an array specified by DC or DS, how to access the i th element of, i.e., [i] label is the base address of this array, i is the index how to calculate the memory address of [i] v Formula to compute address of [i] E: Effective address. The actual element address ase: ase address. The starting address of the array Index: Element index Size: Element size. yte=1, Word=2, Longword=4 Offset: Offset into array to element s position ORG $8300 GRDES DS.W 30 ORG $8200 CLR.W D7 MOVE.L #GRDES, 0 SR 2IN ;read input MOVE.W D2, (0, D7.W) DDI. #2, D7 CMI. #60, D7 NE GRDES ddress Data Index C 830E [0] [1] [2] [3] [4] [5] [6] [7] E = ase + Offset Offset = Size Index so, E = ase + Size Index GRDES + 23 ccessing One-Dimension rrays Two-Dimension rrays M columns a[0,0] a[1,0] [N][M]= a[n-1,0] a[0,m-1] a[n-1,m-1] N rows v How to store 2-dimension arrays in memory? Row-major order: row 0, row 1,, row N-1 Column-major order: column 0, column 1,, column M-1 Row-Major rray Layout Row-Major rray Layout v Formula to compute address of [i][j] E: ase: Row: Row index Col: Column index NCols: #columns in matrix Size: Element size. RowOffset: Offset into matrix to element s row ColOffset: Offset into row to element s position E = ase + RowOffset oloffset RowOffset = Row Size NCols ColOffset = Size Col so, E = ase + Size (Row NCols ol) ase ddress Data Index [0][0] [0][1] [0][M-1] [1][0] [1][1] [1][M-1] [N-1][0] [N-1][1] [N-1][M-1] row 0 row 1 row N-1 2

3 Column-Major rray Layout v Formula to compute address of [i][j] E: ase: Row: Row index Col: Column index NRows: #rows in matrix Size: Element size. ColOffset: Offset into matrix to element s column RowOffset: Offset into column to element s position E = ase oloffset + RowOffset ColOffset = Col Size NRows RowOffset = Size Row so, E = ase + Size (Col NRows + Row) ase ddress Data Index [0][0] [1][0] [N-1][0] [0][1] [1][1] [N-1][1] [0][M-1] [1][M-1] [N-1][M-1] column 0 column 1 column M-1 Character Strings v character string is a collection of SCII character codes terminated by the byte value 00. ddress Data Char v String related operations search a character or a substring catenation of two strings comparison of two strings string conversions HMSG C 4C 4F H E L L O! 0 Storage llocation v Static storage allocation required storage size is known before the execution of a program storage is only allocated once statically allocated storage size cannot change during program execution allocated storage may not be reused v Dynamic storage allocation what if the required storage size cannot be determined at compile time? allocate or deallocate storage dynamically on a need basis Need special storage management module to manage the storage space for dynamic allocation Linked-Lists v linked-list is a collection of data elements called nodes that are created dynamically and chained by pointers v The size of the linked-list can be changed during program execution, as new nodes adding to the list or node being removed from the list v Node contains two types of items data field pointer field: contains the address of the next node, thus to form the link data Link Node Linked-Lists Linked-List Operations Node 1 Node 2 Node 3 C T 0 v Search a node v dd a new node before the head node v dd a new node after the tail node ( ) Node 1 C 00F Node v Insert a new node before/after a particular node v Delete a node from the list head tail 00F78000 Node 3 T

4 Linked-List Operations: Insert a Node Node 4 inary Trees v binary tree is composed of nodes that contain a data field and two link fields pointing to its left child and right child if existing ( ) Node 1 C 00F S Node v The first node of the tree is called root node, and nodes without children nodes are called leaf data 00F78000 Node 3 T 0 left child right child inary Tree Traversals v re-order traversal ccess data field ccess left child ccess right child v In-order traversal ccess left child ccess data field ccess right child v ost-order traversal ccess left child ccess right child ccess data field +C +C inary-tree ost-order Traversal (recursive) v ssume data field holds a word value. 6 points to the root node. OST MOVE.L 6, -(7) ;push 6 onto stack CM.L #0, 6 EQ EXIT MOVE.L 6, -(7) MOVE.L 2(6), 6 ;get left child pointer SR OST ;recursive call MOVE.L (7)+, 6 MOVE.L 6(6), 6 ;get right child pointer SR OST ;recursive call MOVE.L (7)+, 6 MOVE.W (6), D1 ;read data field MOVE. #1, D0 TR #15 EXIT MOVE.L (7)+, 6 RTS +C Stacks and Queues (user created) asic rogram Structures v Stack (LIFO): the last item pushed is always the first item popped Operations: USH (data onto the stack), O (data off the stack) Maintenance: stack pointer, bottom-of-stack pointer, top-of-stack pointer v Queue (FIFO): the first item loaded is the first item to be removed Operations: ENQUEUE (add a new item to the slot pointed by the tail pointer), DEQUEUE (remove the item from the slot pointed by the head pointer) Maintenance: head pointer, tail pointer, queue size v The underlying storage implementation of stacks and queues can be based on either linked-lists or arrays v IF-THEN, IF-THEN-ELSE v REET-UNTIL Loop v WHILE-DO/FOR Loop v SWITCH-CSE 4

5 IF-THEN-ELSE v IF <condition> Then <action> if condition is true, action will be executed if (x == 0) CMI. #0, D5 <action> NE ;<action> v IF <condition> Then <action1> ELSE <action2> if condition is true, action1 will be executed, otherwise, action2 will be executed if (x == 0) CMI. #0, D5 <action1> EQ THENCODE else ELSECODE ;<action2> <action2> R THENCODE ;<action1> REET-UNTIL Loop v REET-UNTIL loop test the condition at the end of each iteration If condition is True, then exist the loop If condition is false, continue the next iteration Note that the 1 st iteration will be always executed Note that the loop variable(s) determining the <condition> should be updated within the loop repeat GIN ;<loop body> <loop body> SUI. #1, D2 ;update loop cnt until <condition> NE GIN ;if == 0 x == 0 WHILE-DO, FOR Loops v WHILE-DO loop performs the condition test at the beginning of each loop iteration If the condition is True, then execute the loop iteration, and repeat Otherwise, exit the While loop Note that the loop variable(s) determining the <condition> should be updated during the loop For loop can be converted into an equivalent WHILE loop while <condition> do WHILE CMI. #0, D2 ;update loop cnt <loop body> EQ ;if =0, exit ;<loop body> ;update D2 R WHILE x!= 0 SWITCH-CSE Statement v CSE statement is used to test a variable/expression against multiple values, which determines the corresponding action switch <item> case <val_1>: <statements 1> case <val_2>: <statements 2> (test value in D1) CMI. #0, D1 ;is it 0? case <val_x>: <statements x> NE C1 default: <default statements> ;C0 action R ;exit C1 CMI. #1, D1 ;is it 1? NE C2 ;C1 action R ;exit C2 5