BlitzScript3D Engine's Compiler parses *.bs/*.bsc source code and generates PCode instructions *.bso that are executed by the Virtual Machine. I selected this method over interpreting for speed and security.

I started with Mark Sibly's Compiler Code because it had a excellent way of parsing expressions and tokenizing BASIC statements, keywords, etc and output instructions. With some research and reading on Assembler, I was armed with enough info to pursue development of BlitzScript3D. The best way to get a feel for the internal workings of the compiler is to examine the bscvmCompiler.bb.

Extremely High Level Overview

The Compiler consists of 8 functions that work together recursively to generate Pcode:

1. bscvmCompilerLoad()
2. bscvmCompilerTokenGet()
2. bscvmCompilerParseStatement()
3. bscvmCompilerParseExpession()
4. bscvmCompilerParseTerm()
5. bscvmCompilerParseFact()
6. bscvmCompilerParseLeaf()
7. bscvmCompilerParseArguments()

The bscvmCompilerLoad() loads *.bsc file line by line. The bscvmTokenGet() parses the line by one character at a time returning a BSCVM_TOKEN that represents a Keyword, Value, Array, Variable, or CALL to the function that called it, usually the bscvmCompilerStatement().

The bscvmCompilerStatement() is reponsible for generating PCode for Keyword Constructs and Assignments to Variable/Array from the BSCVM_TOKENs returned by bscvmTokenGet().

bscvmCompilerParseExpression() is reponsible generating PCode for Conditions like Equal_to, Greater_than, etc.

bscvmCompilerParseTerm() and bscvmCompilerParseFact() are responsible for generating PCode for math operations.

bscvmCompilerParseLeaf()is reponsible for generating PCode for Keyword Constructs and Assignments from Variable/Array and Calls.

bscvmCompilerParseArguments() generates PCode for generating PCode for Call Parameters.

BlitzBasic3D --> OpCode Conversion

Select...Case

Select a Case 1 a=2 Case 2, 0 a=1 Default a=0 EndSelect ;Select a mov eax,[a] mov ebx, eax ;Case 1 label_2 mov eax,1 cEQ eax, ebx jz label_3 ;a=2 mov eax,2 mov [a], eax jmp label_1 ;Case 2 label_3 mov eax,2 push eax mov eax,0 pop ecx or eax, ecx cEQ eax, ebx jz label_4 ;a=1 mov eax,1 mov [a], eax jmp label_1 ;Default label_4 ;a=0 mov eax,0 mov [a], eax jmp label_1 ;EndSelect label_5 label_1 end

For...Next

For a = 1 To 10 Step 2 b=1 Next ;For a = 1 To 10 Step 2 mov eax,1 mov [a], eax label_2 mov eax, [a] push eax mov eax,10 pop ecx cLT eax, ecx jz label_1 ;b=1 mov eax,1 mov [b], eax ;Next mov eax, [a] add eax, 2.0 mov [a], eax jmp label_2 label_1

Repeat...Until

Repeat a=a-1 Until a=0 ;Repeat label_2 ;a=a-1 mov eax,[a] push eax mov eax,1 pop ecx sub eax,ecx mov [a], eax ;Until a=0 mov eax,[a] push eax mov eax,0 pop ecx cEQ ecx,eax jz label_2 label_1

While...Wend

While a<10 a=a+1 Wend While a<10 label_2 mov eax,[a] push eax mov eax,10 pop ecx cLT ecx,eax jz label_1 ;a=a+1 mov eax,[a] push eax mov eax,1 pop ecx add eax,ecx mov [a], eax ;Wend jmp label_2 label_1