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<h1 id="assignment-3">Assignment 3</h1>
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<p>CMPT 295 – Fall 2021</p>
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<p>Objectives:</p>
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<ul>
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<li>
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<p>Memory addressing modes</p>
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</li>
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<li>
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<p>Assembly instructions</p>
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</li>
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<li>
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<p>Reading object code (machine level instruction) expressed in hexadecimal and
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understanding how these instructions are stored in memory</p>
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</li>
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<li>
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<p>Writing a C program that corresponds to given assembly program</p>
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</li>
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</ul>
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<p>Submission:</p>
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<ul>
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<li>
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<p>Submit your document called Assignment_3.pdf, which must include the number of the
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question you are answering (e.g., Question 1) followed by your answer, keeping the
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questions in their original numerical order. Formatting your assignment document this
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way makes it a lot easier to mark.
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o Add your full name and student number at the top of the first page of your
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document.</p>
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</li>
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<li>
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<p><strong>If you write your answers by hand (as opposed to using a computer application to
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write them)</strong>, when putting your assignment document together, do not take photos of
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your assignment sheets! Scan them instead! Better quality -> easier to read -> easier to
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mark!</p>
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</li>
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</ul>
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<p>Due:</p>
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<ul>
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<li>Friday Oct. 8 at 4pm on CourSys</li>
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<li>Late assignments will receive a grade of 0, but they will be marked (if they are submitted
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before the solutions are posted on Monday) in order to provide feedback to the
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student.</li>
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</ul>
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<p>Marking scheme:</p>
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<ul>
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<li>This assignment will be marked as follows:
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<ul>
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<li>Questions 1, 2 and 3 will be marked for correctness.</li>
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</ul>
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</li>
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<li>The amount of marks for each question is indicated as part of the question.</li>
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<li>A solution will be posted on Monday after the due date.</li>
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</ul>
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<hr />
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<h2 id="1-10-marks-memory-addressing-modes">1. [10 marks] Memory addressing modes</h2>
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<p>Assume the following values are stored at the indicated memory addresses and registers:</p>
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<table>
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<tbody>
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<tr>
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<td>Memory Address</td>
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<td>Value</td>
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</tr>
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<tr>
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<td>0x230</td>
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<td>0x23</td>
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</tr>
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<tr>
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<td>0x234</td>
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<td>0x00</td>
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</tr>
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<tr>
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<td>0x235</td>
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<td>0x01</td>
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</tr>
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<tr>
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<td>0x23A</td>
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<td>0xed</td>
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</tr>
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<tr>
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<td>0x240</td>
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<td>0xff</td>
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</tr>
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</tbody>
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</table>
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<table>
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<tbody>
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<tr>
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<td>Register</td>
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<td>Value</td>
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</tr>
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<tr>
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<td>%rdi</td>
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<td>0x230</td>
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</tr>
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<tr>
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<td>%rsi</td>
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<td>0x234</td>
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</tr>
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<tr>
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<td>%rcx</td>
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<td>0x4</td>
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</tr>
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<tr>
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<td>%rax</td>
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<td>0x1</td>
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</tr>
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</tbody>
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</table>
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<p>Imagine that the operands in the table below are the Src (source) operands for some
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unspecified assembly instructions (any instruction except lea*), fill in the following table
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with the appropriate answers.</p>
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<p>Note: We do not need to know what these assembly instructions are in order to fill the table.</p>
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<table>
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<tbody>
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<tr>
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<td>Operand</td>
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<td>Operand Value (expressed in hexadecimal)</td>
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<td>Operand Form (Choices are: immediate, Register, or one of the 9 Memory Addressing Modes)</td>
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</tr>
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<tr>
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<td>%rsi</td>
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<td> </td>
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<td>Register</td>
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</tr>
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<tr>
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<td>(%rdi)</td>
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<td> </td>
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<td>Indirect memory addressing mode</td>
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</tr>
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<tr>
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<td>$0x23A</td>
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<td> </td>
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<td> </td>
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</tr>
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<tr>
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<td>0x240</td>
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<td>0xff</td>
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<td> </td>
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</tr>
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<tr>
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<td>10(%rdi)</td>
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<td> </td>
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<td>“Base + displacement” memory addressing mode</td>
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</tr>
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<tr>
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<td>560(%rcx,%rax)</td>
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<td> </td>
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<td> </td>
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</tr>
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<tr>
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<td>-550(, %rdi, 2)</td>
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<td> </td>
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<td> </td>
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</tr>
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<tr>
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<td>0x6(%rdi, %rax, 4)</td>
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<td> </td>
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<td> </td>
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</tr>
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</tbody>
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</table>
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<p>Still using the first table listed above displaying the values stored at various memory
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addresses and registers, fill in the following table with three different Src (source) operands
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for some unspecified assembly instructions (any instruction except lea*). For each row,
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this operand must result in the operand Value listed and must satisfy the Operand Form
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listed.</p>
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<table>
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<tbody>
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<tr>
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<td>Operand</td>
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<td>Value</td>
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<td>Operand Form (Choices are: Immediate, Register or one of the 9 Memory Addressing Modes)</td>
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</tr>
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<tr>
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<td> </td>
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<td>0x00</td>
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<td>Absolute memory addressing mode</td>
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</tr>
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<tr>
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<td> </td>
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<td>0x00</td>
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<td>Scaled indexed memory addressing mode</td>
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</tr>
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<tr>
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<td> </td>
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<td>0x00</td>
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<td>Indexed memory addressing mode</td>
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</tr>
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</tbody>
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</table>
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<h2 id="2-2-marks-machine-level-instructions-and-their-memory-location">2. [2 marks] Machine level instructions and their memory location</h2>
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<p>Consider a function called arith, defined in a file called arith.c and called from the
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main function found in the file called main.c.</p>
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<p>This function arith performs some arithmetic manipulation on its three parameters.</p>
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<p>Compiling main.c and arith.c files, we created an executable called ar, then we
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executed the command:</p>
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<pre class="terminal">
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objdump –d ar > arith.objdump
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</pre>
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<p>We display the partial content of arith.objdump below. The file arith.objdump is
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the disassembled version of the executable file ar.
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Your task is to fill in its missing parts, which have been underlined:</p>
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<pre class="terminal">
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0000000000$400527 <arith>:
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400527: 48 8d 04 37 lea (%rdi,%rsi,1),%rax
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______: 48 01 d0 add %rdx,%rax
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40052e: 48 8d 0c 76 lea (%rsi,%rsi,2),%rxc
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______: 48 c1 e1 04 shl $0x4,%rcx
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400536: 48 8d 54 0f 04 lea 0x4(%rdi,%rcx,1),%rdx
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______: 48 0f af c2 imul %rdx,%rax
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______: c3 retq
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</pre>
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<h2 id="3-8-marks-c-program-versus-assembly-program">3. [8 marks] C program versus assembly program</h2>
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<p>Do the Homework Problem 3.58 at the end of Chapter 3. Make sure you satisfy the following requirements:</p>
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<ul>
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<li>Your code must be commented and well spaced such that others (i.e., TA’s) can read
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your code and understand what each instruction does.</li>
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<li>About comments:
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<ul>
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<li>Comment of Type 1: Here is an example of a useful comment: <code class="language-plaintext highlighter-rouge">cmpl %edx, %r8d # loop while j < N</code></li>
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<li>Comment of Type 2: Here is an example of a not so useful comment: <code class="language-plaintext highlighter-rouge">cmpl %edx, %r8d # compare %edx with %r8d</code></li>
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<li>Do you see the difference? Make sure you write comments of Type 1.</li>
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</ul>
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</li>
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<li>You cannot use the goto statement.</li>
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<li>You must write your program using C (not C++) and your program must compile on our <em>target machine</em>.</li>
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</ul>
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<p>Once you have created your program and saved it in a file called decode2.c, generate its
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assembly code version using the optimization level “g” (–Og) and save it in a file called
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decode2.s.</p>
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<p>Include the content of both files decode2.c and decode2.s in your assignment</p>
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<p>Assignment_3.pdf document. Label them well.</p>
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<p>You do not have to electronically submit your files decode2.c and decode2.s on
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CourSys. However, your program must be functionally correct (i.e., it must compile,
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execute properly and solve this problem).</p>
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<footer>
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</footer>
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</div>
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</main>
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</body>
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</html>
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