CPSC 2310 - DAY 3
AUGUST 22, 2016

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High Level Language (HLL)

assembly language - one-to-one correspondence with machine instructions.
represented by 0/1 patterns

Compiler - A translator that translates statements written in HLL into
assembly code, performing various optimizations and register allocations
along the way.

Interpreter - A translator that translates and executes all at the same time.

Assembler - A program that takes assembly instructions and converts them into
machine code that the computer's processor can use to perform its basic
operations.  The result is called an object file.

Compiler calls Assembler

ASSEMBLY LANGUAGE
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. an instruction is composed of 
	.operation code (opcode)
	.operands (names of registers and/or information needed to generate
	a memory address)

labels are placeholders to addresses
each label must be unique

symbolic program (human readable) ----------> machine code (binary)
symbolic labels -> memory addresses
opcodes                              -> bit patterns in instructions
operand id                           -> bit patterns in instructions
immediate operand values (constants) -> bit patterns in instructions

Assemblers have a two-pass structure.
	.instructions can have forward or backward references to labels
	.note that a forward reference requires a two-pass assembly structure
	since you encounter a "use" before its definition and thus cannot 
	immediately translate the label into its memory address

	Two pass structure because FORWARD REFERENCES!

thus:
	pass 1 - increment a location counter as you read each assembly
	language statement and collect any label definitions into a symbol
	table with the corresponding location counter values
	
	pass 2 - translate the assembly language statements using the symbol
	table.

SIMPLIFIED:
	pass 1 - build the symbol table & keep track of location counter.
	pass 2 - Translates into machines code, DOES NOT EXECUTE!

LOCATION COUNTER HOLDS THE COUNTER FOR WHERE WE ARE IN THE PROGRAM DURING
TRANSLATION! (NOT EXECUTION!)

SYMBOL TABLE

-----------------------------------------
|  NEXT            |       103          |
|    X             |       106          |
|   ...            |                    |
-----------------------------------------

IF you keep all the translated code in memory, you can translate in one pass.


ACCUMULATOR MACHINE
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