CSC 2210: Midterm 1 review

• Note 1: motivation for learning C, C++
• Note 2: basic C++
  • Java design goal: run anywhere
    • Type system: ensure computation gives same result regardless of hardware
    • Depend on just-in-time compiler to make things as efficient as possible
    • What is the impact of this on run-time performance?
    • Side-effect: runtime checks for array accesses, pointers, undefined values
  • C/C++ design goal: efficient computation at hardware level
    • Type, runtime system: maximize efficiency, keeping programmers in control of any resources used
  • Simple input/output, basic types, basic operations
  • declarations, sizeof, scope , lifetime, constants, arrays
  • C++ functions, passing arrays
  • overloaded functions, operators, optional arguments
Note 3: computer internals
• types of storage, CPU, memory, bus
• Moore's law, how speed of light is critical to computation
• register, bit, byte, word
• big-endian/byte ordering
• binary, 1s-complement, 2s-complement, hexadecimal
• Note 4: x86 assembly programming
  • 8086, 8087, 80386, Core, I Series processors
  • 8086, 80386, 64-bit register names (especially general purpose registers, stack pointer, stack base pointer)
  • mov, add, sub, imul (2 operand), and, or, xor, not, neg, push, pop
  • .data, .text, .global, ret
  • Why x86 distinguish between movb, movw, movl, movq
• Note 5: labels and addresses
  • What is a label in assembly code?
  • jmp
  • cmp X Y: know it computes Y - X (same as sub)
  • ZF: Y - X == 0
  • SF: sign of result of Y - X
  • CF: carry flag (for now, just know it is set by arithmetic operations)
  • je, jne: jump on ZF
  • jg, jge, jl, jle: if you need to write code with these, we will remind you which flags are used
  • nop, concept of a pseudo-instruction
  • well-defined vs. undefined vs. random
  • stack frame, address
  • (%rXX) vs %rXX
  • see additional concepts in review section to note 5

Exercises

• In C++, read a list of numbers (until end of file) and count the number of 0s
• Convert your solution to the first exercise into a program that reads the data into an array (in main) and then calls a function to compute the number of 0s
• explain the elements of a compiled form of the program you wrote above.
  • Note: it's often easier to describe the code generated by

            g++ -S -O prog.cpp
    

    because the first level of optimization moves computations out of the stack frame and into registers
    • Why would unoptimized code rely heavily on the stack frame?
    • Why would a programmer desire the compiler to use registers instead?
    • What is the cost of this optimization?