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CSCI 305: Programming Languages

Language Systems I

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 Java program? State it as precisely as possible (language-definition time, language-implementation time, compile time, link time, load time, or runtime). Explain how each of the following is bound and why it is bound when it is:

• The location in memory of a local variable in a method.
• The meaning of the keyword while.
• The size of memory of a variable of type int.
• The bytecode for a class.

Check Your Learning

Solution:

• The location in memory of a local variable in a method in Java is bound at load time.
• The meaning of the keyword while in Java is bound at language definition time.
• The size of memory of a varaible of type int in Java is bound at language definition time.
• The bytecode for a class in Java is bound at 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

Using this assembly language, give translations of the following assignment statements. Use as few instructions as possible:

• net := gross - costs
• volume := (length * width) * height

Check Your Learning

Solution Video - (04:51)

Solution:

• net := gross - costs

   load gross, r1
   load costs, r2
   sub r1, r2, r1
   store r1, net
  

• volume := (length * width) * height

   load length, r1
   load width, r2
   mul r1, r2, r1
   load height, r2
   mul r1, r2, r1
   store r1, volume