Write a program in object code that reads a single digit decimal number and displays its negative in binary. To do this, you must first read the number as a character and then convert it to its numeric value, as discussed in class. Then, you're going to change this to a negative number in two ways:
1. First take its 1's compliment by inverting all its bits (changing all 0's to 1 and 1's to 0) using the "bitwise invert r" instruction. This instruction will at once invert all the bits. After taking its 1's compliment, take its 2's compliment by adding a 1 to it. The accumulator will now contain the negative of the number. To display it, you must get each bit, one by one, and store it as a character so that you can then display the bits as characters. To do that, take the modulus of the number by 2 (And with 1, as discussed in class). If the least significant bit is 1, the modulus will produce a 1, if it's 0, it'll give you a 0. Convert it to character and store. But, note that taking the modulus will overwrite the number in accumulator with the remainder that gets produced. So, before doing the modulus, you must first save the value that's in the accumulator. After saving the first bit, load the number you had saved back into the accumulator. Then, to get the second bit, we must make it the least significant bit in the accumulator. There is an easy way to do that: just shift the number to right once. The second bit will be positioned at the first bit location. Save the number again and do the modulus again, convert the remainder to a character and save it. Do this for three more bits for a total of 5 bits. Why 5? Because to represent the negative of a 0-9 we need 5 bits unlike the unsigned value which requires only 4. Now, you have the five bits saved as characters which you can display.
2. The second way to do this is the same as 1 above with one small difference: instead of first taking the 1's compliment of the number and then its 2's compliment, you can take its 2's compliment directly by using the "Negate r" instruction. This is only slightly shorter as you won't have to add 1. The rest will be the same. When you display the result after doing it this way, you should, of course, get the same result as in 1.
Finally, to check your answer, load the original positive number that you had saved back into the accumulator, add to it the negative number which you had also saved, convert the sum to a character and display the resulting character. It must be a 0.
Load the pepo file and submit.
The following is a sample run of the program:
Input: 8
Output:
-8=11000 (from conversion using bitwise invert instruction)
-8=11000 (from conversion using Negate instruction)
8-8=0
To print a new line, just display the ASCII value of newline.