MIPS%20coding

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MIPS coding
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SPIM

• Some links can be found such as
• http//www.cs.gmu.edu/dnord/cs265/spim_intro.html
  

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A C Sort Example
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A C Sort Example
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A C Sort Example
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A C Sort Example
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A C Sort Example
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Character and String Operations

• Characters are encoded as 0s and 1s using ASCII
  most commonly
• American Standard Code for Information
  Interchange
• Each character is represented using 8 bits (or a
  byte)
• MIPS provides instructions to move bytes
• Load byte (lb) loads a byte to the rightmost 8
  bits of a register
• Store byte (sb) write the rightmost 8 bits of a
  register to memory

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String Copy Procedure
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String Copy Procedure

• Do we have to use s0?

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Arrays vs. Pointers

• Pointers sometime seem difficult to understand in
  C/C
• Here by comparing arrays and pointers in MIPS
  assembly we can have a much better understanding
  of the differences

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C Programs Using Arrays and Pointers
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C Programs Using Arrays and Pointers
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MIPS Assembly Using Arrays

• Register allocations Two parameters are in a0
  (for array) and a1 (for size), and local
  variable i is allocated to register t0

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MIPS Assembly Using Pointers

• Register allocations Two parameters are in a0
  (for array) and a1 (for size), and local
  variable p is allocated to register t0

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Comparing Two Versions

• Suppose the size of array is n, how many
  instructions for the array version?
• How many instructions for the pointer version?

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Comparing Two Versions

• Suppose the size of array is n, how many
  instructions for the array version?
• How many instructions for the pointer version?

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Comparing Two Versions

• Suppose the size of array is n, how many
  instructions for the array version?
• How many instructions for the pointer version?

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Tree Sort

• This example shows to support data structures
  such as nodes in a binary tree
• Binary search tree
• One way to create a sorted list is to insert
  values sequentially into a binary tree, where the
  values in the left tree are no larger than the
  value in the node and the values in the right
  tree are no smaller than the value in the node

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Tree Node

• In C, each tree node will be defined as a
  recursive data structure
• How can we do that in MIPS?
• In MIPS we do not have types explicitly
• The types are defined implicitly based on the
  instructions we use

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Tree Node

• In MIPS, we need three words

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Searching the Tree
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Treesort.s

• It first creates an empty tree by creating a root
  node with empty left and right pointers
• Loop
• Read a new value
• If it is the sentinel value, break out the loop
• Otherwise, insert the value into the tree and
  repeat
• Traverse the tree recursively
• http//www.cs.fsu.edu/zzhang/CDA3100_Spring_2008_
  files/tree_sort.asm

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Note

• Note that a number can be written and saved in
  different ways
• For example, number 1234 can be represented as
  1234 (as a string)
• number 1234 can be represented as a twos
  complement integer

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Number 1234 in Memory
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Addressing Modes

• An addressing mode is a form for specifying one
  or more operands
• Typically one instruction set architecture will
  use multiple forms of addressing modes
• In MIPS, we have five different addressing modes

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MIPS Addressing Modes
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Translating a C Program
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Generated Intel Assembly Example
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Assembler

• The primary task of an assembler is to translate
  assembly into machine code
• It produces an object file, which consists of
  machine language instructions, data, and
  information needed to place instructions properly
  in memory
• A UNIX object file consists of the object file
  header, text segment, static data segment,
  relocation information, symbol table, and
  debugging information
• Which instructions may change depending on the
  absolute locations of instructions?

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Linkers

• Object files need to be combined together in
  order to produce an executable program
• The tool is called the linker
• Searches the libraries to find library routines
  used by the program
• Determines the memory locations for each module
  and relocates its instructions by adjusting
  absolute references
• Resolve any unresolved references among files
  (including libraries)

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Linkers
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Loaders

• Note that an executable file is on the disk
• To run a program, it needs to be loaded into
  memory

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Dynamically Linked Libraries