摘要：今天折騰一上午，終于完成了上這個(gè)課程的最后一個(gè)匯編器項(xiàng)目。這套課程真是沒白跟，收獲良多，現(xiàn)在已經(jīng)等不及想看下一期的軟件部分了，哈哈。

今天折騰一上午，終于 完成了 Coursera 上 From Nand to Tetris / Part I 這個(gè)課程的最后一個(gè)匯編器項(xiàng)目。這套課程真是沒白跟，收獲良多，現(xiàn)在已經(jīng)等不及想看下一期的軟件部分了，哈哈。

下面是我的 python 實(shí)現(xiàn)，存?zhèn)€檔，同時(shí)給同樣在看這課程的同學(xué)們參考。

注釋風(fēng)格看起來可能有點(diǎn)奇怪，拍腦袋想的，沒多少 python 編碼經(jīng)驗(yàn)，還望包涵，稍微解釋一下：

#-----------------#
# 大塊代碼用途描述 #
#-----------------#

## 分級注釋

### 分級注釋

#### 分級注釋

import sys
import os.path


#--------#
# tables #
#--------#

## symbol table

SYMB_TABLE = {
    "SP":     0,
    "LCL":    1,
    "ARG":    2,
    "THIS":   3,
    "THAT":   4,
    "R0":     0,
    "R1":     1,
    "R2":     2,
    "R3":     3,
    "R4":     4,
    "R5":     5,
    "R6":     6,
    "R7":     7,
    "R8":     8,
    "R9":     9,
    "R10":    10,
    "R11":    11,
    "R12":    12,
    "R13":    13,
    "R14":    14,
    "R15":    15,
    "SCREEN": 16384,
    "KBD":    24576
}

## comp table

COMP_TABLE = {
    "0":   "0101010",
    "1":   "0111111",
    "-1":  "0111010",
    "D":   "0001100",
    "A":   "0110000",
    "!D":  "0001101",
    "!A":  "0110001",
    "-D":  "0001111",
    "-A":  "0110011",
    "D+1": "0011111",
    "A+1": "0110111",
    "D-1": "0001110",
    "A-1": "0110010",
    "D+A": "0000010",
    "D-A": "0010011",
    "A-D": "0000111",
    "D&A": "0000000",
    "D|A": "0010101",
    "M":   "1110000",
    "!M":  "1110001",
    "-M":  "1110011",
    "M+1": "1110111",
    "M-1": "1110010",
    "D+M": "1000010",
    "D-M": "1010011",
    "M-D": "1000111",
    "D&M": "1000000",
    "D|M": "1010101"
}

## dest table

DEST_TABLE = {
    "null": "000",
    "M":    "001",
    "D":    "010",
    "MD":   "011",
    "A":    "100",
    "AM":   "101",
    "AD":   "110",
    "AMD":  "111"
}

## jump table

JUMP_TABLE = {
    "null": "000",
    "JGT":  "001",
    "JEQ":  "010",
    "JGE":  "011",
    "JLT":  "100",
    "JNE":  "101",
    "JLE":  "110",
    "JMP":  "111"
}


#------------------#
# helper functions #
#------------------#

## determine is Int

def isInt(str):
    try:
        int(str)
        return True
    except ValueError:
        return False

## determine instruction type

def getInsType(ins):
    if ins[0] == "@":
        return "a"
    return "c"

## split instruction

### instruction A

ram_variable_num = 16

def valueOfAIns(ins):
    global ram_variable_num

    if SYMB_TABLE.has_key(ins[1:]):
        ins = SYMB_TABLE[ins[1:]]
    elif isInt(ins[1:]):
        ins = ins[1:]
    else:
        SYMB_TABLE[ins[1:]] = ram_variable_num
        ram_variable_num += 1
        ins = SYMB_TABLE[ins[1:]]

    bin_value =  bin(int(ins))[2:]
    zero_count = 16 - len(bin_value)
    zero_str =   "0" * zero_count

    return zero_str + bin_value

### instruction C

def splitCIns(ins):
    c_parts = {}

    dest_splited = ins.split("=")
    if len(dest_splited) == 1:
        c_parts["dest"] = "null"
        jump_splited = dest_splited[0].split(";")
    else:
        c_parts["dest"] = dest_splited[0]
        jump_splited = dest_splited[1].split(";")

    if len(jump_splited) == 1:
        c_parts["jump"] = "null"
    else:
        c_parts["jump"] = jump_splited[1]

    c_parts["comp"] = jump_splited[0]

    return c_parts


#------------#
# main logic #
#------------#

## first pass

### source file

sf_name = sys.argv[1]
sf = open(sf_name, "r")

### destination file

df_name = os.path.splitext(sf_name)[0] + ".tmp"
df = open(df_name, "w")

line_num = 0

for ins in sf:
    # comment
    ins = ins.split("http://")[0]

    # white space
    ins = ins.strip()
    if len(ins) == 0: continue

    # label
    if ins[0] == "(" and ins[-1] == ")":
        SYMB_TABLE[ins[1:-1]] = line_num
        continue

    df.write(ins + "
")
    line_num += 1

sf.close()
df.close()

## second pass

### source file

sf_name = os.path.splitext(sf_name)[0] + ".tmp"
sf = open(sf_name, "r")

### destination file

df_name = os.path.splitext(sf_name)[0] + ".hack"
df = open(df_name, "w")

for ins in sf:
    ins = ins.strip()

    ins_type = getInsType(ins)
    if ins_type == "a":
        val = valueOfAIns(ins) + "
"
        df.write(val)
    elif ins_type == "c":
        parts = splitCIns(ins)
        val = "111" + COMP_TABLE[parts["comp"]] + DEST_TABLE[parts["dest"]] + JUMP_TABLE[parts["jump"]] + "
"
        df.write(val)

sf.close()
df.close()