instruction_type = [‘NULL’,’A_INSTRUCTION’,’C_INSTRUCTION’,’L_INSTRUCTION’]
instruction_dest = [‘NULL’,’M’,’D’,’MD’,’A’,’AM’,’AD’,’AMD’]
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instruction_jump = [‘NULL’,’JGT’,’JEQ’,’JGE’,’JLT’,’JNE’,’JLE’,’JMP’]
instruction_comp = [‘NULL’,
‘0’,’1′,’-1′,
‘A’,’M’,’D’,
‘!A’,’!M’,’!D’,
‘-A’,’-M’,’-D’,
‘A+1′,’M+1′,’D+1’,
‘A-1′,’M-1′,’D-1’,
‘D+A’,’D+M’,
‘D-A’,’D-M’,’A-D’,’M-D’,
‘D&A’,’D&M’,
‘D|A’,’D|M’]
class SymbolTable:
def __init__(self):
Symbol table constructor
def addSymbol(self, symbol, value):
Adds a symbol to the symbol table
@param symbol: The name of the symbol
@param value: The address for the symbol
def getSymbol(self, symbol):
Gets a symbol from the symbol table
@param symbol: The name of the symbol
@return: The address for the symbol or -1 if the symbol isn’t in the table
class Assembler:
def doFirstPass(instructions, symbolTable):
Assembler first pass; populates symbol table with label locations.
@param instructions: A list of the assembly language instructions.
@param symbolTable: The symbol table to populate.
def generateMachineCode(instructions, symbolTable):
Translates a set of instructions to machine code.
@param instructions: A list of the assembly language instructions to be converted to machine code.
@param symbolTable: The symbol table to reference/update.
@return: A String containing the generated machine code as strings of 16-bit binary instructions, 1-per-line.
def parseInstructionType(instruction):
Parses the type of the provided instruction
@param instruction: The assembly language representation of an instruction.
@return: The type of the instruction (A_INSTRUCTION, C_INSTRUCTION, L_INSTRUCTION, NULL)
return “NULL”
def parseInstructionDest(instruction):
Parses the destination of the provided C-instruction
@param instruction: The assembly language representation of a C-instruction.
@return: The destination of the instruction (see instruction_dest)
return “NULL”
def parseInstructionJump(instruction):
Parses the jump condition of the provided C-instruction
@param instruction: The assembly language representation of a C-instruction.
@return: The jump condition for the instruction (see instruction_jump)
return “NULL”
def parseInstructionComp(instruction):
Parses the computation/op-code of the provided C-instruction
@param instruction: The assembly language representation of a C-instruction.
@return: The computation/op-code of the instruction (see instruction_comp)
return “NULL”
def parseSymbol(instruction):
Parses the symbol of the provided A/L-instruction
@param instruction: The assembly language representation of a A/L-instruction.
@return: A string containing either a label name (L-instruction),
a variable name (A-instruction), or a constant integer value (A-instruction)
def translateDest(dest):
Generates the binary bits of the dest part of a C-instruction
@param dest: The destination of the instruction
@return: A String containing the 3 binary dest bits that correspond to the given dest value.
return “000”
def translateJump(jump):
Generates the binary bits of the jump part of a C-instruction
@param jump: The jump condition for the instruction
@return: A String containing the 3 binary jump bits that correspond to the given jump value.
return “000”
def translateComp(comp):
Generates the binary bits of the computation/op-code part of a C-instruction
@param comp: The computation/op-code for the instruction
@return: A String containing the 7 binary computation/op-code bits that correspond to the given comp value.
return “0000000”
def translateSymbol(symbol, symbolTable):
Generates the binary bits for an A-instruction, parsing the value, or looking up the symbol name.
@param symbol: A string containing either a label name, a variable name, or a constant integer value
@param symbolTable: The symbol table for looking up label/variable names
@return: A String containing the 15 binary bits that correspond to the given sybmol.
return “000000000000000”
# A quick-and-dirty parser when run as a standalone script.
if __name__ == “__main__”:
import sys
if(len(sys.argv) > 1):
instructions = []
# Open file
with open(sys.argv[1], “r”) as a_file:
# Read line-by-line, skip comments and empty line
for line in a_file:
if line[0] != ‘/’ and line[0] != “\n”:
instructions.append(line.strip())
symbolTable = SymbolTable()
# First pass
Assembler.doFirstPass(instructions,symbolTable)
# Second pass
code = Assembler.generateMachineCode(instructions,symbolTable)
# Print output
print(code)
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