Introduction to SIMPLE

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# Introduction to SIMPLE - PowerPoint PPT Presentation

Introduction to SIMPLE A reduced instruction set High Level Language (HLL) The Simple programming Language Simple has only 7 statements rem - the remainder of the line is a comment input - read from the keyboard print - write to the terminal goto - jump to a line number

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### Introduction to SIMPLE

A reduced instruction set High Level Language (HLL)

1BA3 – G Lacey – Semester 1 Lecture 4

The Simple programming Language
• Simple has only 7 statements
• rem - the remainder of the line is a comment
• input - read from the keyboard
• print - write to the terminal
• if/goto - if a condition is true jump to another line
• let - evaluate a mathematical expression
• end - end of the program
• Every line has a line number
• Simple only operates on integers
• Simple only has lower case
• Variable names have a single letter

1BA3 – G Lacey – Semester 1 Lecture 4

The Simple programming Language
• Variables can only be integers and do not need to be declared before being used
• Simple mathematical operators
• Addition, subtraction, multiplication, division are +, -, *, /
• greater than >, greater than or equal to >=
• less than <, less than or equal to <=
• equal to ==, not equal to !=
• assign the value to =
• parentheses ( )
• Examples
• 10 rem this is a comment
• 22 input x
• 33 if x == 0 goto 10
• 40 let r = a + b * c / ( a - d )
• 50 print x

1BA3 – G Lacey – Semester 1 Lecture 4

sum = a + b

print sum

end

Determine and print the sum of two numbers

10 rem add and print the sum of 2 nums

20 input a

30 input b

40 let c = a + b

50 print c

60 end

1BA3 – G Lacey – Semester 1 Lecture 4

true

if a > b

false

print a

print b

end

Print the larger of 2 numbers

1BA3 – G Lacey – Semester 1 Lecture 4

Print the larger of two numbers
• 10 input a
• 20 input b
• 30 if a >= b goto ? x
• 40 print b
• 50 goto ? y
• x 60 print a
• y 70 end

1BA3 – G Lacey – Semester 1 Lecture 4

Compute the sum of a series of positive numbers
• Series is terminated by a negative number
• Maximum number of integers in the series is 10
• This problem was solved in a previous lecture using SML

1BA3 – G Lacey – Semester 1 Lecture 4

sum = 0

counter = 0

true

if a < 0

false

true

if counter

== 10

print sum

false

counter +1

end

sum + a

Compute the sum of a series of positive numbers

1BA3 – G Lacey – Semester 1 Lecture 4

Compute the sum of a series of positive numbers

10 rem read series of numbers and print sum

12 rem initialise counter and sum

15 let c = 0

20 let s = 0

22 rem start programme

25 input x

30 if x > 0 goto ?

35 if c == 10 goto ?

40 let c = c + 1

45 let s = s + x

47 rem restart loop

50 goto 40

53 rem print sum and end programme

55 print s

60 end

1BA3 – G Lacey – Semester 1 Lecture 4

### A SIMPLE to SML Compiler

An introduction to the concepts in translating HLL into Assembly

1BA3 – G Lacey – Semester 1 Lecture 4

Compilers
• Compilers translate High Level Languages (HLLs) like Java and C++ into Machine code
• Two reasons for using HLLs
• Ease of programming
• It is easier to solve large problems using HLLs because most of the machine specific detail is hidden.
• Machine Independence
• Different processors use different instruction sets. This detail is taken care of by the compiler. Thus a c++ program written on a mac will also compile on a p.c.

1BA3 – G Lacey – Semester 1 Lecture 4

Translating Simple to Simpletron Machine Language
• Compiling a Simple programme involves translating the Simple Code to SML
• Each Simple statement has to be translated into SML instructions
• Each variable must be allocated memory space
• Each constant must be allocated memory space

1BA3 – G Lacey – Semester 1 Lecture 4

Compiling Simple
• Allocating Data Space for variables and constants
• start at the max memory and work down.
• E.G. in Simpletron begin by allocating memory space 99, then 98, 97...
• Compiling Instructions
• Instructions are placed at the bottom of memory working up.
• E.G. in Simpletron the processor always starts at 00. The first instruction is placed at 00, the next at 01, then 02 ...
• Running out of space
• If the programme is too big (too much code and too many variables and constants) the instruction space will run into the data space.

1BA3 – G Lacey – Semester 1 Lecture 4

Example Production Rules for translating Simple into SML
• 10 input x
• input corresponds to the READ operation SML thus the operator part of the SML instruction is 10
• x is a variable and must be allocated memory space if none has been allocated already.
• the instruction placed in memory location 00 is 1099
• 20 print x
• print corresponds to the WRITE operator in SML thus the operator is 11
• x has already been allocated memory location 99
• the instruction in memory location 01 is 1199
• 30 goto 10
• goto corresponds to the BRANCH operator in SML thus the operator is 40
• the instruction compiled from line number 10 was placed in memory location 00 thus the operand is 00
• the instruction 4000 is placed in memory location 02
• 40 end
• corresponds to HALT in SML thus 4300 goes into location 03

1BA3 – G Lacey – Semester 1 Lecture 4

Example Compilation

Simple Code SML Instructions

10 input x

20 print x

30 goto 10

40 end

1BA3 – G Lacey – Semester 1 Lecture 4

More Complex Production Rules
• To translate if and goto statements the compiler must generate more than one statement.
• First :
• load x into the accumulator
• Second :
• branch if accumulator is zero to instruction from line number 10

Simple SML

10 input x

20 if x == 0 goto 10

1BA3 – G Lacey – Semester 1 Lecture 4

Another Example

Simple SML

10 input x

20 input y

30 if x > y goto 10

1BA3 – G Lacey – Semester 1 Lecture 4