CS 147

June 13, 2001

Levels of Programming Languages

Svetlana Velyutina

Overview

Levels of programming languages.

Their relationship to each other.

How they’re converted into executable form.

How Java applets are converted to run on a computer.

Attributes of assembly language instructions.

• High- Level Languages

• Assembly Languages

• Machine Languages

LANGUAGE CATEGORIES

• platform independent

• highest level of abstraction

• Java, C++, FORTRAN

High- Level Languages

Assembly Languages

• lower level of abstraction

• specific to each microprocessor

• usually backward compatible

• can directly manipulate data stored in a microprocessors internal components

• platform-specific

• contain binary values

• platform specific

• each microprocessor has own language

• may be backward compatible

Machine Languages

High-level Language Programs are Compiled

Other Pentiumobject files

W indow sPentium PC

Pentuimexecutable file

Pentium linker

Pentium object code

Com piler for PentiumW indow s PC

Other G 4object files

G 4Pow er M ac

G 4executable file

G 4 linker

G 4 object code

Com piler for G 4Pow er M ac Com puter

Other SPARCobject files

SPARCUNIX w orkstation

SPARCexecutable file

SPARC linker

SPARC object code

Com piler for SPARCUNIX w orkstation

High level-languagesourse code

Assembly Language Programs are Assembled

Other processor X object files

Com puter w ith processor X

Processor Xexecutable file

Processor X linker

Processor X object code

Assem bler forprocessor X

Assem bly languageprogram for processor X

Java Applets are Compiled into Bytecode

W indow sPentium PC

Java VM forW indow s Pentium PC

G4Pow er M ac

Java VM forG4 Pow er M ac

SPARCUNIX w orkstation

Java VM forSPARC UNIX w orkstation

Bytecode

Java com piler

Java appletsource code

Applet is a Java program running inside a browser.

Bytecode• Bytecode is generated by Java compiler to be

later interpreted by Java Virtual Machine and translated into machine code at run-time.

• JVM interprets the bytecode for its specific platform and executes it.

• Therefore, bytecode is platform independent.

• JVM can be a hardware chip but usually it is a program, often part of Web browser.

• Most browsers are Java-enabled and most operating systems have JVM ported on them.

Bytecode• Bytecode can not be directly executed by

microprocessor - code runs much slower

• Therefore it would not be efficient to do CPU-intensive tasks with JVM interpreter

• Still Java can easily keep up with the data rate of network connection.

• Many platforms have just-in-time bytecode compilers that compile code once, cach the results and call it again if needed.

• Just-in-time compilers will speed up the program 10 - 20 times compare to interpreter.

Attributes of Assembly Language Instructions

• instruction types

• data types

• addressing modes

• instruction formats

Assembly Language Instruction Types

• data transfer instructions

• data operation instructions

• program control instructions

• interrupts

• halt instruction

• most common microprocessor operation

• copy the value to its destination

• perform following transfers:– Load data from memory into the

microprocessor

– Store data from microprocessor into memory

– Move data within the microprocessor

– Input data to the microprocessor

– Output data from the microprocessor

Data Transfer Instructions

Data Operation Instructions

• Arithmetic, Logic and Shift instructions

• modify their data values

• perform operation on one or two data values and store result

Program Control Instructions

• jump or branch instructions used to go to another part of program

• absolute jump is always taken: jr $ra

• conditional jump is taken if condition is met: bne $t0, $t1, endloop

• instructions to call and return from subroutines: jal calcsqrt

Interrupts

• tells microprocessor to stop and execute

another instruction

• software interrupts are generated by assembly language instructions

• hardware interrupts are triggered by devices outside of microprocessor

Halt instruction

• causes microprocessor to stop executing instructions

• used at the end of program

Most Common Data Types

• Integers

• Floating point numbers

• Boolean values

• Characters

Integers

• range from 0 to 2^n - 1 for unsigned

• from -2^n to 2^(n-1)-1 for signed

Floating Point Numbers

• include fractional portion of the value

• may be assigned special registers

and instructions by microprocessor

Boolean Type

• true or false values

• zero is false, non-zero is true• can be used to perform logical

operations• Ex.: result of 0010 AND 0001 is true

Characters

• stored as binary values

• encoded using ASCII, EBCDIC, UNICODE or other encoding standard

Addressing Modes

• Direct Mode: LDAC 5 (loads value into accumulator from memory location 5)

• Indirect Mode: LDAC @5 (loads value from the memory address stored at memory location 5)

• Register Direct Mode: LDAC R (copies value stored in register R)

• Register Indirect Mode: LDAC @R (copies value from the memory address stored in register R)

Assume LDAC loads data from memory into microprocessor’s AC register.

Addressing Modes

• Immediate Mode: LDAC #5 (moves value 5 into accumulator)

• Implicit Mode: LDAC (gets an operand from stack, don’t have to specify an operand)

• Relative Mode: LDAC $5 (the operand supplies offset from the program counter to generate address)

• Index Mode: LDAC 5(X) (loads the data from X+5 memory location)

• Address Mode: LDAC 5(X) (loads the data from memory address(X+5))

Instruction Formats

Instructions code - binary value representing an assembly language instruction after it is converted into machine code.

Different instructions may have different formats.

Groups of bits in a format correspond to the opcode and the operands.

Example for the operation A=B+CThis instruction has one operation, two source

operands and one destination operand.

Microprocessor performing 16 different operations will need 4 bits to specify one operation.

Assume bit pattern 1010 corresponds to addition.

Assume that there are only 4 possible operands for this operation A, B, C and D.

Corresponding bit patterns for the operands: 00 for A, 01 for B, 10 for C and 11 for D.

Instruction Formats

opcode operand #1 operand #2

4 bits 2 bits 2 bitsMOVE A,B (A=B) 1000 00 01

ADD A,C (A=A+C) 1010 00 10

opcode operand #1 operand #2 operand #3

4 bits 2 bits 2 bits 2 bits

ADD A,B,C (A=B+C) 1010 00 01 10

assembly code machine code

Format for three-operand instruction.

Format for two-operand instruction.

Instruction Formats

opcode operand

4 bits 2 bits

LOAD B (Acc=B) 0000 01ADD C (Acc=Acc+C) 1010 10STORE A (A=Acc) 0001 00

opcode

4 bits PUSH B (Stack=B) 0101PUSH C (Stack=C,B) 0110ADD (Stack=B+C) 1010POP A (A=Stack) 1100

assembly code machine code

One-operand instruction. The accumulator register is always used as destination and one of source registers.

Zero-operand instruction. All operands are drawn from the stack.

Instruction Formats

Microprocessor may be designed to work with instructions that specify 3, 2, 1 or 0 operands.

Microprocessor that uses two-operand instructions is more limited than one using three-operand instructions.

Microprocessors with Fewer Operand Instructions

Drawbacks:• more instructions needed for the same task

Benefits: • instruction codes use fewer bits

• hardware to implement microprocessor is less complex

• microprocessors whose instructions specify fewer operands can usually execute instructions more quickly