CS 300

1
CS 300 Lecture 8

• Intro to Computer Architecture
• / Assembly Language
• Branching and Function Calling

2
Homework 4

• Will be in the wiki SOON!

3
Operations So Far

• Arithmetic add, sub, addi (why not subi?)
• Memory access lw, sw What next?
• Byte oriented memory access
• lb, lbu, sb, lh, lhu, sh Signed and unsigned
• Byte /
  halfword
• Logical operations
• and
• or
• nor
• left shift, right shift (logical)

4
Packed Structures

• What sort of code sequences do packed structures
  require? Note that C doesn't explicitly support
  packing at the bit level but C programmers can
  use shifts / logical operations to simulate this.
• typedef struct a
• long a
• char b
• short c
• short d __attribute__((packed)) A

5
And, Or, Not

• Note that these operations are really easy to
  implement in hardware!!
• In C. these are , , and
• Mips and, andi, or, ori, nor
• How do we use these with bit field constants?

6
Shifting

• The other logical operation is shifting
• Shift left
• Shift right
• Arithmetic shift right (not in MIPS)
• Circular shifting (not in MIPS)
• This is ltlt and gtgt in C
• What does shifting do to the arithmetic value of
  a number?

7
Program Flow

• Unconditional Jump instructions (j)
• Conditional beq, bne (register comparisons)
• Set instructions to capture booleans (not
  really a program flow instruction but similar!)
• How do you compile if, while, for, case, ???

8
Dynamic Memory Management

• Dynamic memory is used to handle memory needs
  that can't be anticipated statically.
• Two forms
• Stack based for objects that are no longer
  needed upon function exit
• Heap based for objects that have "indefinite"
  extent.
• In Java, you can't see the difference between
  these. In C, all local variables are stack
  based only malloc() used the heap. Need to
  explicitly free heap objects.

9
Sharing Memory

• On the MIPS, memory is allocated to a process as
  follows

Stack
Unused
Heap
Static memory allocation
Stack Pointer (sp)
If the pointers cross, you're out of memory
Heap Pointer (gp)
code, constants, static vars, system stuff