2.1.2 Thinking Ahead

• Thinking Ahead

  planning inputs and outputs.

  • what answers do we need?
  • how can we turn the inputs into required outputs?
  • what do we need to know?
• Identifying inputs and outputs

  
• Preconditions

  Requirements which must be met before a program can run
• Caching

  • process of storing instructions or values in cache memory after they have been used, as they may be used again
  • saves time which would have been needed to store and retrieve the instructions from secondary storage again.
  • content can be loaded without any delay. This also means images and text do not have to be downloaded again multiple times, freeing up bandwidth for other tasks on a network
• Prefetching

  • Loading a resource before it is needed
  • algorithms predict which instructions are likely to soon be fetched
  • less time is spent waiting for instructions to be loaded into RAM from the hard disk
• Limitations of Prefetching

  • accuracy of the algorithms used in prefetching, only provide an informed prediction and there is no guarantee that this will be right
  • cache size limits how much data can be stored
• Reusable Program Components

  • Commonly used functions are often packaged into libraries for reuse
  • include: implementations of abstract data structures such as queues and stacks as well as classes and subroutines.
• Pros of Reusable Program Components

  • save time for programmer
  • save on development costs for project
  • Reliable and bug free
  • optimised by experts
• Example of reusable program components

  In a game there will be pre-written code for:

  • high score table
  • movement control
  • rendering of images
  • timer routines