Midterm Exam with Cheat Sheet - Computer Architecture II | CS 232, Exams of Computer Architecture and Organization

Download Midterm Exam with Cheat Sheet - Computer Architecture II | CS 232 and more Exams Computer Architecture and Organization in PDF only on Docsity! 1 CS232 Midterm Exam 1 February 18, 2002 Name: • This exam has 6 pages, including this cover and the cheat sheet on the next page. • There are three questions worth a total of 100 points. • You have only 50 minutes, so budget your time! • No written references or calculators are allowed. • To make sure you receive full credit, please write clearly and show your work. • We will not answer questions regarding course material. Question Maximum Your Score 1 30 2 40 3 30 Total 100 2 MIPS Instructions These are some of the most common MIPS instructions and pseudo-instructions, and should be all you need. However, you are free to use any valid MIPS instructions or pseudo-instruction in your programs. Category Example Meaning add $t0, $t1, $t2 $t0 = $t1 + $t2 sub $t0, $t1, $t2 $t0 = $t1 - $t2 addi $t0, $t1, 100 $t0 = $t1 + 100 mul $t0, $t1, $t2 $t0 = $t1 * $t2 move $t0, $t1 $t0 = $t1 Arithmetic li $t0, 100 $t0 = 100 lw $t0, 100($t1) $t0 = Mem[100 + $t1]Data Transfer sw $t0, 100($t1) Mem[100 + $t1] = $t1 beq $t0, $t1, Label if ($t0 == $t1) go to Label bne $t0, $t1, Label if ($t0 != $t1) go to Label bge $t0, $t1, Label if ($t0 >= $t1) go to Label bgt $t0, $t1, Label if ($t0 > $t1) go to Label ble $t0, $t1, Label if ($t0 <= $t1) go to Label Branch blt $t0, $t1, Label if ($t0 < $t1) go to Label slt $t0, $t1, $t2 if ($t1 < $t2) then $t0 = 1; else $t0 = 0 Set slti $t0, $t1, 100 if ($t1 < 100) then $t0 = 1; else $t0 = 0 j Label go to Label jr $ra go to address in $raJump jal Label $ra = PC + 4; go to Label The second source operand of sub, mul, and all the branch instructions may be a constant. Register Conventions The caller is responsible for saving any of the following registers that it needs, before invoking a function: $t0-$t9 $a0-$a3 $v0-$v1 The callee is responsible for saving and restoring any of the following registers that it uses: $s0-$s7 $ra Performance Formula for computing the CPU time of a program P running on a machine X: CPU timeX,P = Number of instructions executedP x CPIX,P x Clock cycle timeX CPI is the average number of clock cycles per instruction, or: CPI = Number of cycles needed / Number of instructions executed 5 Question 2 continued Part (b) Our code is somewhat slow, since expensive multiplication operations are executed repeatedly. Rewrite the function to eliminate both multiplications from the main body of the loop. (20 points) Ostrich: bge $a1, $a2, Duck mul $t1, $a1, 4 add $t1, $a0, $t1 mul $t2, $a2, 4 add $t2, $a0, $t2 lw $t3, 0($t1) lw $t4, 0($t2) sw $t3, 0($t2) sw $t4, 0($t1) addi $a1, $a1, 1 sub $a2, $a2, 1 j Ostrich Duck: jr $ra Part (c) What is the CPU time in nanoseconds for 100 loop iterations of your revised function? (10 points) Instruction class CPI mul 5 branches and jumps 3 data transfers 3 all others 1 6 Question 3: Writing a nested function (30 points) Show how to translate the pseudocode below for SelectionSort into a MIPS assembly language function. This algorithm first finds the largest element in A[0]..A[n] and moves it to position n, then finds the largest element in A[0]..A[n-1] and puts that in position n-1, and so forth. • You will not be graded on the efficiency of your code, but you must follow all MIPS conventions. • Assume that you already have a MIPS function MaxIndex, which takes two arguments A and n, and returns the index of the largest element of A[0]..A[n]. The arguments and return values are passed in registers $a0, $a1 and $v0 respectively. • Remember that integers are 32-bit, or 4-byte, MIPS quantities. SelectionSort(A, n) for i = n downto 1 m = MaxIndex(A, i) // Find the largest element in A[0]..A[i] exchange A[i] and A[m] // Move it to position i