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Subroutines in ARM assembly assignment help

The assignment deals with the evaluation of a given arithmetic expression with 4 variables. The variable values are read from the user by first reading a numerical string and then converting it to decimal. The expression is then evaluated and the result is printed using a subroutine that converts the number to a string to be displayed. The addresses of the variables used to hold the values are printed in hexadecimal. The following solution demonstrates the approach we follow to do your homework when you take ARM assembly assignment help from us.

Evaluation of a Given Arithmetic Expression

Subroutines in ARM assembly assignment help

.data strMessage1: .asciz "Name: your name" strMessage2: .asciz "\nClass: CS 3B" strMessage3: .asciz "\n Lab: RASM1" strMessage4: .asciz "\nDate: 2/18/2019\n\n" strPrompt: .asciz "Enter a whole number: " strEqOpen: .asciz "(" strEqSum: .asciz " + " strEqClose1: .asciz ") - (" strEqClose2: .asciz ") = " strMessage5: .asciz "\nThe address of the 4 ints:\n" strMinus: .asciz "-" strTab: .asciz "\t" strLF: .asciz "\n" strVal: .skip 11 @ space to save a maximum of 10 ascii digits + a zero for each number numBuffer: .skip 20 @ buffer for conversions hexTable: .asciz "0123456789ABCDEF" .balign 4 A: .word 0 B: .word 0 C: .word 0 D: .word 0 X: .word 0 .text .global _start @ provide a program starting address to Linker .equ BUFSIZE,10 @ Size of input buffer .balign 4 _start: ldr r1, =strMessage1 @ Title Message1 bl putstring @ Call subroutine to print message ldr r1, =strMessage2 @ Title Message2 bl putstring @ Call subroutine to print message ldr r1, =strMessage3 @ Title Message3 bl putstring @ Call subroutine to print message ldr r1, =strMessage4 @ Title Message4 bl putstring @ Call subroutine to print message ldr r1, =strPrompt @ Message asking for input of first number bl putstring @ Call subroutine to print prompt ldr r1, =strVal @ Set point to input buffer mov r2, #BUFSIZE @ Maximum number of bytes to receive bl getstring @ Call subroutine to get keyboard input ldr r0, =strVal @ convert first number to integer bl convert ldr R1, =A @ save result in variable A str R0, [R1] ldr r1, =strPrompt @ Message asking for input of second number bl putstring @ Call subroutine to print prompt ldr r1, =strVal @ Set point to input buffer mov r2, #BUFSIZE @ Maximum number of bytes to receive bl getstring @ Call subroutine to get keyboard input ldr r0, =strVal @ convert second number to integer bl convert ldr R1, =B @ save result in variable B str R0, [R1] ldr r1, =strPrompt @ Message asking for input of third number bl putstring @ Call subroutine to print prompt ldr r1, =strVal @ Set point to input buffer mov r2, #BUFSIZE @ Maximum number of bytes to receive bl getstring @ Call subroutine to get keyboard input ldr r0, =strVal @ convert third number to integer bl convert ldr R1, =C @ save result in variable C str R0, [R1] ldr r1, =strPrompt @ Message asking for input of fourth number bl putstring @ Call subroutine to print prompt ldr r1, =strVal @ Set point to input buffer mov r2, #BUFSIZE @ Maximum number of bytes to receive bl getstring @ Call subroutine to get keyboard input ldr r0, =strVal @ convert fourth number to integer bl convert ldr R1, =D @ save result in variable D str R0, [R1] ldr r1, =strEqOpen @ Print first part of equation bl putstring @ Call subroutine to print prompt ldr r0, =A @ print value of A ldr r0, [r0] bl printInteger ldr r1, =strEqSum @ Print sum bl putstring @ Call subroutine to print prompt ldr r0, =B @ print value of B ldr r0, [r0] bl printInteger ldr r1, =strEqClose1 @ Print closing parenthesis and sum bl putstring @ Call subroutine to print prompt ldr r0, =C @ print value of C ldr r0, [r0] bl printInteger ldr r1, =strEqSum @ Print sum bl putstring @ Call subroutine to print prompt ldr r0, =D @ print value of D ldr r0, [r0] bl printInteger ldr r1, =strEqClose2 @ Print closing parenthesis and equal sign bl putstring @ Call subroutine to print prompt @ calculate equation result: ldr r0, =A ldr r0, [r0] ldr r1, =B ldr r1, [r1] ldr r2, =C ldr r2, [r2] ldr r3, =D ldr r3, [r3] add r0, r0, r1 @ (A+B) add r1, r2, r3 @ (C+D) sub r0, r0, r1 @ (A+B) - (C+D) ldr r1, =X str r0, [r1] @ save result in variable bl printInteger @ print result in screen ldr r1, =strMessage5 @ Print address message bl putstring @ Call subroutine to print prompt ldr r0, =A @ print address of A bl printHexadecimal ldr r1, =strTab @ Print tab bl putstring @ Call subroutine to print string ldr r0, =B @ print address of B bl printHexadecimal ldr r1, =strTab @ Print tab bl putstring @ Call subroutine to print string ldr r0, =C @ print address of C bl printHexadecimal ldr r1, =strTab @ Print tab bl putstring @ Call subroutine to print string ldr r0, =D @ print address of D bl printHexadecimal ldr r1, =strLF @ Print line feed bl putstring @ Call subroutine to print string mov r0, #0 @ Exit Status code set to 0 to indicate "normal completion" mov r7, #1 @ service command code (1) will terminate this program svc 0 @ Issue Linux command to terminate program @ Subroutine to divide by 10 @ R0: number to divide @ On return: @ R0: number divided by 10 @ All registers are preserved div10: push {R1-R3} @ Preserve working register contents. ldr R1, =0xCCCCCCCD @ special value used for dividing by 10 umull R2,R3,R1,R0 @ divide r0 by 10 mov R0, R3, LSR #3 @ put r0=r0/10 pop {R1-R3} @ Restore saved register contents bx LR @ Return to the calling program. @ Subroutine to convert a numeric ascii string to a integer @ R0: Points to the string to convert @ On return: @ R0: Converted number @ All registers are preserved convert: push {R1-R4} @ Preserve working register contents. mov R1, R0 @ save pointer to string in R1 mov R0, #0 @ put sign in R0, assume positive mov R4, #0 @ R4 will have converted number, init to zero ldrb R2, [R1] @ load first character from the string cmp R2, #'-' @ see if the number was negative bne startcnv @ if not, start conversion add R1, R1, #1 @ skip sign character mov R0, #1 @ put sign in R0, is negative startcnv: ldrb R2, [R1] @ load character from string cmp R2, #48 @ if it's end of string, end conversion blt endcnv sub R2, R2, #48 @ convert ascii digit to integer mov R3, #10 mul R4, R3, R4 @ multiply old number by 10 add R4, R4, R2 @ add digit add R1, R1, #1 @ advance to next character in string b startcnv endcnv: cmp R0, #0 beq retpos neg R4, R4 @ if negative, convert to negative retpos: mov R0, R4 @ return converted number pop {R1-R4} @ Restore saved register contents bx LR @ Return to the calling program. @ Subroutine to print an integer @ R0: number to print @ All registers are preserved printInteger: push {R0-R6, LR} @ Preserve working register contents. ldr R5, =numBuffer @ point to buffer to save conversion add R5, R5, #10 @ point to end of buffer mov R1, #0 @ save end of string in the conversion buffer strb R1, [R5] mov R6, #3 @ r6 will count the comma positions mov R2, R0 @ save number in R2 cmp R2, #0 @ see if the number was negative bge startp @ if not, start print neg R2, R2 @ else, convert number to positive ldr r1, =strMinus @ print minus sign bl putstring @ Call subroutine to print the string startp: mov R0, R2 @ divide number by 10 bl div10 mov R3, #10 @ calculate remainder to get digit mul R4, R0, R3 sub R4, R2, R4 add R4, R4, #48 @ convert digit to ascii add R5, R5, #-1 strb R4,[R5] @ save in buffer subs R6, R6, #1 @ decrement comma counter bne skip mov R6, #3 @ reload counter cmp R0, #0 @ see if there are still digits to print beq skip @ if not, don't put a comma mov R4, #',' add R5, R5, #-1 strb R4,[R5] @ else save comma in buffer skip: movs R2, R0 @ repeat while the number is not zero bne startp mov R1, R5 @ print resulting conversion bl putstring pop {R0-R6, LR} @ Restore saved register contents bx LR @ Return to the calling program. @ Subroutine to print an integer as a 32 bit hexadecimal @ R0: number to print @ All registers are preserved printHexadecimal: push {R0-R5, LR} @ Preserve working register contents. ldr R1, =numBuffer @ point to buffer to save conversion ldr R2, =hexTable @ point to hex conversion table with R3 ldr R3, =#28 @ number of times to shift number ploop: lsr R4, R0, R3 @ shift to the right to get next hex digit and R4, R4, #0xF @ mask to leave only 4 bits ldrb R4, [R2, R4] @ get conversion to hex using table strb R4,[R1],#1 @ save in buffer subs R3, R3, #4 @ decrement number of times to shift bge ploop @ repeat while the shift is not negative ldr R0, =#0 strb R0,[R1] @ save end of string char ldr R1, =numBuffer @ print resulting conversion bl putstring pop {R0-R5, LR} @ Restore saved register contents bx LR @ Return to the calling program. .end @ Subroutine Provided a pointer to a space to sa ve a null terminated @ string, and a number of byutes to read, it will read a string from @ the terminal @ R1: Points to a buffer to save the read string @ R2: Contains the number of the bytes to read @ LR: Contains the return address @ All registers are preserved. .global getstring @ Subroutine entry point. getstring: push {R0-R3,R7} @ Preserve working register contents. mov R0, #1 @ Code for stdin (standard input, i.e., keyboard) mov R7, #3 @ Linux service command code to read string. svc 0 @ Issue command to read string from stdin mov R2, #0 strb R2, [R1, R0] @ save a zero at the end of the string pop {R0-R3,R7} @ Restore saved register contents bx LR @ Return to the calling program. .end @ Subroutine Provided a pointer to a null terminated string, putstring will @ display the string to the terminal @ R1: Points to a null terminated string @ LR: Contains the return address @ All registers are preserved. .global putstring @ Subroutine entry point. putstring: push {R0-R3,R7} @ Preserve working register contents. mov R2, #0 @ R2 will store the length of the string. mov R3, R1 @ Copy R1 into R3 nxtchar: ldrb R0,[R3],#1 @ Load next character from string. subs R0, #0 @ Subtract the null bias. beq print @ if (zero flag is set) @ branch to print section @ else add R2, #1 @ increment length by 1 b nxtchar @ branch to top of loop print: mov R0, #1 @ Code for stdout (standard output, i.e., monitor) mov R7, #4 @ Linux service command code to write string. svc 0 @ Issue command to display string on stdout pop {R0-R3,R7} @ Restore saved register contents bx LR @ Return to the calling program. .end