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CSCI 305: Programming Languages

Language Systems II

Reading: Webster Ch. 4

Instructions

1. Watch This Video - (22:57)
2. Watch This Video - (33:19)
3. Review the Lecture Slides
4. Complete the Out of Class Exercise
5. Check your learning
6. Attend Class and complete the In Class Exercises
7. Check your learning

Out of Class Exercise

Exercise

What is the binding time for each of the following in a C or C++ program? State the binding time as precisely as possible (langugae-definition time, language-implementation time, compile time, link time, load time, or runtime).

• The location in memory of a global static variable.
• The code for the printf function
• The type of a local variable in a function.

Check Your Learning:

Solution:

• The location in memory of a global static variable => Load Time
• The code for the printf function => Link Time
• The type of a local variable in a function => Compile Time

In Class Exercises

Exercise

Suppose the target assembly language for a compiler has these five instructions for integers:

   load address,reg
   add reg,reg,reg
   sub reg,reg,reg
   mul reg,reg,reg
   store reg,address

In these instructions, and address is the name of a static variable (whose actual address will be filled in by the loader). A reg is the name of an integer register, a special extra-fast memory location inside the processor. The target assembly language has three integer registers: r1, r2, and r3. The load instruction loads the integer from the given memory address into the given register. The add instruction adds the second register to the first register and places the result in the third register. The sub instruction subtracts the second register from the first register and places the result in the third register. The mul instruction multiplies the first register by the second register and places the result in the third register. The store instruction stores the integer from the given register at the given memory address. So, for example the compiler might translate the assignment result := offset + (width * n) into this:

   load width, r1
   load n,r2
   mul r1,r2,r1
   load offset,r2
   add r2,r1,r1
   store r1,result

1. Create a machine language to match the provided assembly language. That is, give a binary encoding of the instruction set, so that each possible instruction has a unique encoding as a string of bits. Assume that addresses require 16 bits. Choose an encoding that is simple (so it could be implemented in hardware efficiently) but not unnecessarily wasteful of space. Different instructions need not be the same length, as long as the machine-language programs are unambiguous. Show the format you use for each instruction. Show the translation of this assembly-language program into your machine language:

load width, r1
load n, r2
mul r1, r2, r1
load offset, r2
add r2, r1, r1
store r1, result

Check Your Learning:

A Solution:

Instruction	code
load	000
add	001
sub	010
mul	011
store	100

width  = 01010110 01101001
offset = 11010010 00110101
n      = 10001001 00100101
result = 11100110 11101010

r1 001
r2 010
r3 100

000 01010110 01101001 001
000 10001001 00100101 010
011 001 010 001
000 11010010 00110101 010
001 010 001 001
100 001 11100110 11101010