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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

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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

• goto - jump to a line number

• 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

• 10input a

• 20input b

• 30if a >= b goto ?x

• 40print b

• 50goto ?y

• x60print a

• y70end

• 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

SimpleSML

10 input x

20 if x == 0 goto 10

1BA3 – G Lacey – Semester 1 Lecture 4

### Another Example

SimpleSML

10 input x

20 input y

30 if x > y goto 10

1BA3 – G Lacey – Semester 1 Lecture 4