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MIPS coding
SPIM
• Some links can be found such as:
http://www.cs.gmu.edu/~dnord/cs265/spim_intro.html
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 0’s and 1’s 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? 1 6n
• 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? 1 6n
• How many instructions for the pointer version?
3 4n
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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 two’s
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
1. Immediate addressing
Operand is constant
op
rs
rt
Immediate
2. Register addressing
Operand is in register
op
rs
rt
rd
...
funct
Registers
Register
3. Base addressing
op
rs
rt
Memory
Address
lb $t0, 48($s0)
+
Register
Byte
Halfword
Word
4. PC-relative addressing
bne $4, $5, Label
op
(label will be assembled into
a distance)
j Label
rs
rt
+
PC
Word
5. Pseudodirect addressing
op
Address
Memory
Word
PC
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Memory
Address
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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
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