Assignment 1 for CSCI 431

1. In this problem you are asked to write some low-level code using a very simple hypothetical machine language. You will use a fairly standard assembly language notation to represent machine code instructions.

   The hypothetical computer has instructions of the form (using assembly language notation)

   op r,d(b)

   where r and b are registers and d is a nonnegative number. The register r is an operand register, and d(b) represents the memory address (b) + d, where (b) denotes the contents of register b.

   The instruction set (op codes) is:

   ld - load the word at (b)+d into register r

   st - store the contents (word) in register r at address (b)+d

   a - add the integer at (b)+d to the integer in register r

   m - multiply the integer in register r by the integer at (b)+d

   Thus, for example, the instructions

   ld r1,4(r2)
   st r1,16(r2)

   would copy the word at (r2)+4 to (r2)+16. Assume that there are up to eight general purpose registers (r1 ... r8) to work with.

   Exercise: What code could a compiler generate for the C code

   x = y + 5;
   y = n + m;

   if the following represents the current environment (at the time the above instructions are executed), where each memory cell represents a word of 4 bytes and each byte has an address?

   
   
         ___________          |            |
        |           |         |____________|
    r1: |      -------------->|            |
        |___________|      x: |            |
                              |____________|
                              |            |
                           y: |            |
                              |____________|
                              |            |
                              |         5  |
                              |____________|
                              |            |
                           p: |         -------
                              |____________|   \
                              |            |    \       |            |
                              |            |     \      |____________|
                                                  ----->|            |
                                                     n: |            |
                                                        |____________|
                                                        |            |
                                                     m: |            |
                                                        |____________|
                                                        |            |
   

   
   
2. For each of the following binding times for programming language components, give an example of a property in C that has the binding time.

   Language definition

   Language implementation

   Translation

   Link edit

   Load

   Execution