Problems for Assignment #6

Learning Outcomes: 1) writing assembly code in the 'nasm' or ARM language; 2) writing C code to call 'nasm' or ARM functions; 3) writing functions in C; 4) writing programs in 'nasm' or ARM that call C functions; and 5) writing programs in C that call 'nasm' or ARM functions

1. Using a previous homework problem with code from our stanley/penguin language as your guide, write an assembly program using nasm or ARM called findGCD.nasm or findGCD.arm which will find the GCD of the two numbers. Test your program using the numbers 3113041662 and 11570925 which should produce the value 462837. Read the two numbers from the keyboard at port stdin and write the result to port stdout.
2. Copy your program from the previous problem to a new file called findGCDfunc.nasm or findGCDfunc.arm. Change the code to be a nasm or ARM function which is able to be called from a C program. Then write a program gcdFinder.c containing the code in C to call your new function. Use the assert() functions from the C assert library to test that your GCD finder code is working properly. You can link the assert library into your program by using #include <assert.h> as you've seen in class. Your assembly code should take the two numbers as arguments which are passed from the C code.
3. Parity is a term which is applied when counting the number of bits that are set to 1 in a sequence of bits. It is used to help guarantee that nothing has gone wrong with the bit sequence during transmission. Parity is calculated based on the number of 1 bits in a byte, and a ninth bit, the parity bit, is either set or cleared to achieve the proper parity, either even or odd. For example, for the byte 01101001, assuming even parity, the parity bit would be cleared so that the count of 1 bits remains even for all nine bits; for the byte 10101110, assuming even parity, the parity bit would be set so that the count of 1 bits remains even. Note that the parity bit IS NOT PART of the byte, IT IS A NINTH BIT which is separate from the byte in question.
   Write a nasm function called paritygen.nasm that will count the one bits in a byte of data and print the proper value for the parity bit assuming we are using odd parity. Note that if there is an even number of ones, your program will print a 1 and if there is an odd number it will print a 0.
4. In networking, it is necessary to make sure that bytes are transimitted in the proper order so the receiving device can interpret them correctly. This requires that big-endian and little-endian values are converted to something called Network Byte Order before they are transmitted. For this problem, write a C program whichEndIsUp.c that will determine whether your computer is big-endian or little-endian as was discussed in class.
5. Building on the previous problem, write a C function makeNBOC.c that takes a number as an argument, checks to see if the order needs to be swapped to make Network Byte Order, and swaps its byte order, if necessary. Modify a copy of your previous program from problem 4, whichendisup.c, to make a function that will determine the byte order and if it will need to be swapped. You can also research the hton() and ntoh() functions to do the swapping [if you like]. Write a test program makeNBOtest.c to call your new function and display the results of the function call on stdout using printf().
6. EXTRA CREDIT PROBLEM: Finally, create a nasm or ARM program called makeNBON.nasm or makeNBON.arm which does the byte order swapping BY CALLING YOUR C function from problem five. Make your nasm or ARM program call the function at least five times with different values to test it. The output of each test case should display on the terminal window.