TreeCalc Tree Organized Calculations in Java or JavaScript

Home | Source, Repos

TreeCalc Virtual Machine

Stefan Neubauer

• TU Wien/Fakultät für Informatik
• Virutal Machines / SS 2012 / 185.A49 UE / 28.6.2012

Contents:

• Setting
• Components
• Tc Intermediate Language
• Tc Assembler
• Tc Bytecode - Formulas
• Tc Virtual machine - Data
• Tc Virtual machine - Execution
• TcVM – Tree access
• Results
• Lessons learned

Setting

• Starting point
  • TreeCalc language + Java generator
  • Test models and test data (JUnit)
• Goal
  • Virtual Machine with same functionality
  • Implementation in Java

Components

TODO: Add pic

Tc Assembler Generator

• Variables
  • Numbers instead of names
  • Enhance symbol tables
• Nice and useful
  • Comments in output (variable names, …)
  • Constants handled by Assembler
• Short-circuiting and, or
  • label-handling

Tc Intermediate Language

.tcs:

A_LI_MainLayers.compute =
  F_LI_Indexation_Perc > 0 ? F_LI_TariffDuration : 1

TODO: Add Down Arrow Tc Assembler Generator

.tci:

.formula formula=506 simple=false ; line 3182
    //start of if statement, line 3182
    : callfunc 65 0 ; F_LI_INDEXATION_PERC
    : pushconst 0
    : cmpbig
    : iffalse L0
    : callfunc 90 0 ; F_LI_TARIFFDURATION
    : goto L1
  L0:
    : pushconst 1
  L1:
    //end of if statement
    : return
.formuladone

Tc Assembler

• Configuration: Instructions array

   new Instruction(INSTR_CALLFUNC, "callfunc",
                   +1, -2,
                   "funcid", OPTYPE_INT,
                   "nargs", OPTYPE_BYTE
       ) //arg1 ... arg_nargs -- result
  

• Main action

  • Parsing (ANTLR) + Error handling
  • Formulas
    • Manage constant pool
    • Resolve labels (backpatching)
    • Encode bytecode

Tc Bytecode - Formulas

TODO: Add pic

Tc Virtual machine - Data

TODO: Add pic

Tc Virtual machine - Execution

• Decode instruction -> instrid, op1, op2, op3, op4
• switch(instrid) { … }
• Operand stack

  • set freed elements to null -> automatic GC

    case INSTR_ADD: //a b -- a+b
       stack[sp-1] = V.getInstance(stack[sp-1].doubleValue() + stack[sp].doubleValue());
       stack[sp--] = null;
       break;
    

• Trace
  • PC, instruction, operands
  • status before+after instruction execution
• Base classes
  • Values: V, VString, VDouble, VList, …
  • TreeCalc standard functions
  • Table access functions

TcVM – Tree access

• Macro programs for tree access
  • need special instructions
    • dynamic call of formula
    • get children / linked nodes
    • check if result is defined (own/subnodes)
    • …
  • quite long (~2 x 200 instructions)
  • hard to debug
• Alternatives
  • recursive call to TcVM machine
  • tree actions / results in extra stacks

Results

TODO: Add pic

Lessons learned

• Assembler
  • very useful layer
  • easy to implement

TODO: Add list/block separator <

• Bytecode
  • compact vs. easy to handle
• Assembler generator
  • locatability of instruction names important
  • simpler than Java source code generator
• Virtual machine
  • for prototype: optimize later
  • trace output essential
  • tree handling: macro programming not best solution