Program requests and reads in exactly one character, which represents an exponent. If the value is acceptable, then the program reads in another value. The program calculates the base 2 power between the user input values, and then stores the calculated values in an array. It then prints the values in the array.
# Assignment 3: Powers of 2 Assembly utilizing Array # by Hanly De Los Santos # Copyright ©2009, Hanly De Los Santos. All Rights Reserved. # http://www.hdelossantos.com # # Program requests and reads in exactly one character, # which represents an exponent. If the value is acceptable, then the # program reads in another value. The program calculates # the base 2 power between the user input values, and then # stores the calculated values in an array. It then prints the # values in the array. # .text .globl __start # Load acceptable ascii decimal value for number ranges # since input is read in as a character. __start: li $8, 48 # This is the decimal equivalent of 0 li $9, 57 # This is the decimal equivalent of 9 # Prompt the user for input. la $11, prompt puts $11 # Grab user input and store value in register 10 getc $10 la $11, newline # Create new line lb $17, ($11) putc $17 add $15, $10, 0 # Make copy of contents of r10 in r15. sub $15, $15, 48 # Convert char from first input to int. # Test to determine whether or not the user input value is acceptable. # If user input is less than 48 and greater than 57, branches to # exit_donothing, where the user is told the input is wrong. bgt $10, $9, exit_donothing blt $10, $8, exit_donothing sub $10, $10, 48 # After check, convert char to int. # Prompt user for additional input la $11, prompt2 puts $11 # Grab user input and store in r12 getc $12 la $11, newline # Create new line lb $17, ($11) putc $17 add $18, $10, 0 # Make copy of contents of r12 in r18. sub $18, $18, 48 # Convert char to int. # Test to determine whether or not the user input value is acceptable. # If user input is less than 48 and greater than 57, branches to # exit_donothing, where the user is told the input is wrong. bgt $12, $9, exit_donothing blt $12, $8, exit_donothing sub $12, $12, 48 # After check, convert char to int. # Determine if the difference between the two user input values is 0 bnez $10, neqz beqz $12, special_zero # Determine difference between 2 values neqz: sub $21, $12, $10 #Store diff of the two values in r21 bltz $21, exit_printgtr add $21, $21, 1 # If the value was acceptable, proceed to calculate the power. li $11, 2 # Load multiplier value into $11. li $17, 2 # Initialize 17 to multiplier value # Check to see if the second usr input is > 1, if it is modify r10 so that # the calculations can be made properly. This sets r10 = 2. If the second # input is == 1, then print the results. Must also load 2 into 2nd array # location here in case the seond input is 1. la $16, powers li $22, 1 mult $11, $22 mflo $11 sw $11, 4($16) li $23, 1 beq $23, $12, print_result bgt $10, $23, cont_gtn li $10, 2 # Multiplication loop. While $10 != 0 keep multiplying $17 by 2, and # decrement $10 by 1 every time this is done. Once $10 == 0, store # the result. cont_gtn: sub $10, $10, 1 # Since 2^1 has been taken care of add $14, $10, 0 add $24, $10, 0 add $24, $24, 1 multiply_for: mult $17, $11 # Loop to determine the power val mflo $17 sub $10, $10, 1 bnez $10, multiply_for # The result is stored in the location of the user input * 4, which would # give the matching address location on the array. This loops to # multiply_for while the $10 is != $12. nextval: add $10, $14, 0 # Restores r10 from copy mul $14, $24, 4 # Calculation to determine the add $23, $16, $14 # location in which to place the sw $17, ($23) # resulting power in the array. add $10, $10, 1 # Increment the counters for next add $24, $24, 1 # iteration. add $14, $10, 0 li $17, 2 # restore the multiplier value blt $10, $12, multiply_for beq $10, $12, print_result # Display the value of the exponential function. This loops through the # values in the array starting at the first user input until the # difference between the first and last user input is 0. print_result: la $14, str3 puts $14 # Print out "2^" li $v0, 1 move $a0, $15 syscall # Print out value of user input. la $16, str4 puts $16 # Print out '=' li $v0, 1 la $20, powers # Calculation to determine the mul $19, $15, 4 # location of the power value. add $23, $20, $19 lw $17, ($23) move $a0, $17 syscall # Print out result. la $13, newline # Create new line lb $12, ($13) putc $12 sub $21, $21, 1 add $15, $15, 1 bnez $21, print_result b endofline # Print out the result for 2 to the power of 0 if teh two user # inputs are 0 (special case). special_zero: la $14, str3 puts $14 # Print out "2^" li $v0, 1 move $a0, $15 syscall # Print out value of user input. la $16, str4 puts $16 # Print out '=' li $v0, 1 la $20, powers lw $17, ($20) # Print first value of array. move $a0, $17 syscall la $13, newline # Create new line lb $12, ($13) putc $12 b endofline # If second input is less than or not equal to first input, print mbgtrthan. exit_printgtr: la $13, mbgtrthan puts $13 # If the input is not appropriate, print str2 and exit. exit_donothing: la $13, str2 puts $13 b endofline # This is the exit statement. endofline: done # END OF PROGRAM # Define strings which will be used throughout program .data prompt: .asciiz "Enter a digit '0'-'9': " prompt2: .asciiz "Enter another digit '0'-'9': " mbgtrthan: .asciiz "Second digit must be greater than or equal to the first digit.\n" str2: .asciiz "Bad user input. Quitting.\n" str3: .asciiz "2^" str4: .asciiz " = " newline: .byte '\n' .align 4 powers: .word 1:10 # Create a 10-element int array.