CSE 361S Intro to Systems Software Lab #4

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1 Due: Thursday, October 13, 2011 CSE 361S Intro to Systems Software Lab #4 Introduction In this lab, you will write a program in both assembly and C that sums a list of scores for a set of students, assigns grades to each of the students, and creates frequency and grade distribution tables for the all the students. The frequency and grade distributions will be printed to the screen as a histogram using ASCII characters. In Part I of the lab, you will generate the assembly code for the program, and in Part II of the lab, you will generate the equivalent C code, using pointers, for the program. In both Parts I and II, you have already been given the code organization and the code for printing out the score and grade distributions to the screen; you only need to complete the other portions of the program. For this lab, you are allowed to work in groups of up to 2 individuals. If you do work as a group, you need only make one submission of the group's work. Part I: Assembly Programming Record Format The list of student records will be included in your source file using the.include directive, so you can access the data as you would any other variables. You should keep the test files in the same directory as your assembly file, so that the.include declaration used in the given assembly file will always work:.include "test1.dat" Note: In verifying your program, you will need to change the name of the test file in the.include directive (and re-assemble after each change of the file name) to test the six different test files provided. Within each of the given input files, there are two variables. The first variable is scores, a record list in which each record provides a list of scores for a student. The second variable is numrec, which indicates the number of records in the record list scores. Each record contains a seven character ASCII id field (padded to seven characters with blanks, if needed), followed by the C end-of-string character, 0 (NULL). After the ID string, there are five unsigned word-size (16 bit) scores, a dword-size (32 bit) total field (initialized to 0), a single ASCII character field, grade (initialized to 'F'), and an end-of-record byte, 0 (NULL). The format is shown in the table below, where 'A' indicates an ASCII character, 'B' indicates an unsigned integer byte, 'W' indicates a word, and 'D' indicates a dword. An offset field is provided for your benefit for determining the necessary offset of each of the fields (note: you must determine these offsets yourself). 1

2 Field ID 0 Score 1 Score 2 Score 3 Score 4 Score 5 Total Grade EOR Data AAAAAAA A W W W W W D A B Offset The contents of the test1.dat file is shown below: /* Test1.dat - First data file for CSE 361S - Lab 4 */ /* Format: id, 0, score1, score2, score3, score4, score5, total, grade, 0 */ /* NOTE: the 0 after id is the string terminator for the id string */ scores:.byte 'H', 'a', 'p', 'p', 'y', ' ', ' ', 0, 98, 0, 100, 0, 92, 0, 89, 0, 99, 0, 0, 0, 0, 0, 'F', 0.byte 'G', 'r', 'u', 'm', 'p', 'y', ' ', 0, 91, 0, 86, 0, 93, 0, 89, 0, 88, 0, 0, 0, 0, 0, 'F', 0.byte 'S', 'n', 'e', 'e', 'z', 'y', ' ', 0, 80, 0, 79, 0, 83, 0, 85, 0, 72, 0, 0, 0, 0, 0, 'F', 0.byte 'D', 'o', 'p', 'e', 'y', ' ', ' ', 0, 72, 0, 68, 0, 63, 0, 75, 0, 71, 0, 0, 0, 0, 0, 'F', 0.byte 'B', 'a', 's', 'h', 'f', 'u', 'l', 0, 64, 0, 63, 0, 62, 0, 59, 0, 60, 0, 0, 0, 0, 0, 'F', 0.byte 'S', 'l', 'e', 'e', 'p', 'y', ' ', 0, 51, 0, 48, 0, 47, 0, 53, 0, 50, 0, 0, 0, 0, 0, 'F', 0.byte 'D', 'o', 'c', ' ', ' ', ' ', ' ', 0, 40, 0, 41, 0, 33, 0, 49, 0, 35, 0, 0, 0, 0, 0, 'F', 0 numrec:.int 7 Output Format The frequency distribution should be output to the screen as a histogram using ASCII characters. There should be one row of output per bin in the distribution table. Each row should start with a label indicating the range of scores which that row represents. Following the label should be one star '*' for each total in that range. Following output of the histogram should be a listing of the total number of grades of each type given. The output which corresponds to the test1.dat file is shown below: 0-50: : : : * : * : : ** : * : * : * Number of A's: 2 Number of B's: 3 Number of C's: 1 Number of D's: 1 Number of F's: 0 2

3 Program Details Your program has four main tasks: 1. Total the scores for each record. Each record contains a list of five word-size scores, followed by a dword-size total field (initialized to 0), and an ASCII character field for the grade. For each record your program should add together the five scores and place the sum in the corresponding total field. The scores are stored as unsigned integer words and all are in the range of (inclusive). Each total should be stored as an unsigned integer dword. This operation is to be performed by the compute_totals procedure. The skeleton of this procedure has been provided and you are to fill in the necessary code. 2. Compute the grade for each record. Based on the total, a grade should be given for that score. Scores are to be graded using a uniform distribution (i.e., NOT graded on a curve) that assigns an A to the top 20% of all possible scores, a B to the next 20%, and so on, down to an F for the lowest 20% of all possible scores. This operation is to be performed by the compute_grades procedure. The skeleton of this procedure has been provided and you are to fill in the necessary code. You can receive extra credit by appropriately using a jump table for the grade computation for each record. 3. Fill in the distribution arrays. An array, num_scores, with ten elements has been provided, in which you are to compute the number of records whose total fall within that 50 point range. That is, element 0 should contain the number of records whose total falls between 0 and 50 (inclusive), element 1 should contain the number of records whose total falls between 51 and 100, and so on, up to element 9 which should contain the number of records whose total falls between 451 and 500. Each element in the array has been initialized to 0. This array is then used for printing out the results by the last procedure in the main program. Similarly, an array, num_grades, with five elements has been provided, in which you are to compute the number of students that receive each of the five possible grades. The first element should contain the number of records for students receiving an 'F', the second element should contain the number of records for students receiving a 'D', and so on. Each element in the array has been initialized to 0. This array is then used for printing out the results by the last procedure in the main program. This should be done with only one pass over the data. These operations are to be performed by the create_hist procedure. The skeleton of this procedure has been provided and you are to fill in the necessary code. 3

4 4. Output the histogram and total number of grades for each grade level to the screen. The output should follow the format given above. Be sure to test all of the input files (by changing the file name referenced by the.include directive in the assembly file) and compare your output with the given output files. This code has been provided for you in the procedure, print_results. Implementation For the first part of the lab, students will need the program skeleton hist_asm.s, the Makefile, and the given input and output files: Input: test1.dat, test2.dat, test3.dat, test4.dat, test5.dat, test6.dat Output: out1.txt, out2.txt, out3.txt, out4.txt, out5.txt, out6.txt You can download all the files in the following tar file on the class webpage: cse361s_lab4.tar. Part II: C Programming In the second part of this lab, students are to implement the same functions from Part I in C. The C program skeleton (including the display functions) are provided. Add the necessary C code and verify correctness once again using the six output text files. Note: The test files are now defined in the C syntax as header files (.h files), and use the scores_rec data structure, as defined in each of the header files. To include a given test file, the #include "test1.h" directive is used in the main C program file, (hist_c.c). Similar to Part I, to test the six different input data sets, you will need to change this file name and re-compile the C program after each name change. Don't forget to edit the Makefile to reference the different.h files as well. In the provided C program skeleton, a new pointer variable, rec_ptr, has been declared in hist_c.c. Please use this pointer variable for performing all memory accesses to/from the scores array of records. Set the pointer to the address of each scores array record, as needed, using the technique discussed in class. Note however, that referencing fields in a data structure accessed via a pointer uses a different syntax; instead of a period ('.') between the main variable name and the data structure field, you need to use the pointer symbol ('->') between the pointer variable name and the data structure field. For example, when rec_ptr is pointing to one of the array records (of type scores_rec) in scores, then to access the contents of the grade field in that record, the syntax would be rec_ptr->grade. Note that no asterisk ('*') is needed before rec_ptr to access the contents of the grade field. Comparison of C and Assembly Once the C version of the program is complete, compare the execution time of the C version versus the assembly version. Unfortunately, the run times of these two programs are not sufficiently long enough to measure the time using the time command as we did in Lab #3. Instead, we can compare the two versions by 4

5 measuring the number of machine instructions executed while running each of the two versions. A benefit of this comparison method is that we can tabulate the number of instructions needed to execute each of the individual procedures, which provides more information than the time measurement method. The tool valgrind is commonly used to make these kinds of measurements. Technically, valgrind doesn t really execute your code on the physical machine, but instead executes your code in a simulator that can count things like number of instructions, cache misses, etc. We will use it to count executed instructions. The command line for this is valgrind -tool=callgrind./hist_asm for measuring the assembly language program and valgrind -tool=callgrind./hist_asm for measuring the C program. After execution, a file with the name callgrind.out.<pid> is greated, where <pid> is the process id of the execution. Issuing the command callgrind_annotate callgrind.out.<pid> will provide a (somewhat) human-readable printout of the performance information collected by valgrind. Use the test2 input (i.e. test2.dat and test2.h) for measuring the number of machine instructions executed in the procedures compute_totals(), compute_grades(), and create_hist(). Tabulate the results for each of the above functions in the two programs and discuss the results of this experiment. Are the results for the C program better or worse than the assembly program? How do the two versions compare on a per procedure basis? Are the results what you expected, or were you expecting different results? Why? Exit gdb (if it's still running, it shouldn t be because you should have just been using valgrind), and execute the man gcc command. In particular, look at the various options for the '-O' flags. How would you expect the C program's performance to change when using different levels of '-O' (i.e. -O0 vs. -O1 vs. -O2, etc.)? How would you expect the C program's performance to be different when using '-O' versus not using '-O'? Try changing this flag in the Makefile and measure the actual difference in the number of machine instructions needed for one procedure. Implementation For the second part of the lab, students will need the program skeleton hist_c.c, the Makefile, and the given input and output files: Lab Report Input: test1.h, test2.h, test3.h, test4.h, test5.h, test6.h Output: The output files are the same as in Part I. You can download all the files in the following tar file on the class webpage: cse361s_lab4.tar. When you turn in your assignment, prepare a.tar file containing all your code and the lab report. No hard copies are required. Upload the.tar file to telesis, with your name and lab number in the file name (i.e., use the filename convention we ve used all semester to date: <lastname><firstinitial>_lab4.tar). 5

6 If you worked as a group, make sure both names are in the file name of the submitted report (e.g., <lastname1><firstinitial1>_<lastname2><firstinitial2>_lab4.tar). Either team member can upload your submission to telesis. Be sure to include the assembly source code, hist_asm.s, you created in Part I of the lab in the.tar file. Be sure to include the C source code, hist_c.c, you created in Part II of the lab in the.tar file. In your.tar file, include a file report4.txt. This file should contain your answers, measurements, and discussion for Part II of the lab, the comparison between C and assembly. 6