一个求四则运算的程序,我有些地方不是很明白,哪位高手帮我做点注释!谢谢啦!

B_P     EQU BYTE PTR
W_P     EQU WORD PTR
D_P     EQU DWORD PTR
CODE    SEGMENT
ASSUME  CS:CODE,DS:CODE
        ORG 100H
;主程序开始
NEWSTAR:
        JMP STAR
        EVEN
NUM1    DW 0,0
NUM2    DW 0,0
NUM3    DW 0,0
JGV4    DW 0,0
YSF     LABEL WORD
YSF1    DB 0
YSF2    DB 0
JUV     DB 0
UV      DB 0
;使DS:SI指向第一有效字符
OVERS   LABEL NEAR
        CLD
        PUSH AX
OVERS1:
        LODSB
        CMP AL,' '
        JZ OVERS1
        CMP AL,9
        JZ OVERS1
        DEC SI
        CMP AL,13
        POP AX
        RET
;输出一个制表符
TAB     LABEL NEAR
        MOV AL,9
        JMP SHORT DISP
;输出一个回车换行符
CRLF    LABEL NEAR
        MOV AL,13
        CALL DISP
        MOV AL,10
;显示一个字符
DISP    LABEL NEAR
        PUSH AX
        PUSH DX
        MOV AH,2
        MOV DL,AL
        INT 21H
        POP DX
        POP AX
        RET
;检查是否为运算符
ISYSF   LABEL NEAR
        CLD
        LODSB
        CALL ISJJ
        JZ ISYSF1
        CALL ISII
        JZ ISYSF1
        DEC SI
ISYSF1:
        RET
;检查是否是加减运算
ISJJ    LABEL NEAR
        CMP AL,'+'
        JZ ISYSF1
        CMP AL,'-'
        RET
;检查是否为乘除运算
ISII    LABEL NEAR
        CMP AL,'*'
        JZ ISYSF1
        CMP AL,'/'
        JZ ISYSF1
        CMP AL,'\'
        RET
;数据输出
;CX=10 十进制
;CX=16 十六进制
DOUT    LABEL NEAR
        PUSH AX
        PUSH BX
        PUSH DX
        PUSH BP
        XOR BP,BP
DOUT1:
        INC BP
        PUSH AX
        MOV AX,DX
        XOR DX,DX
        DIV CX
        MOV BX,AX
        POP AX
        DIV CX
        PUSH DX
        MOV DX,BX
        OR BX,AX
        JNZ DOUT1
DOUT2:
        POP AX
        ADD AL,'0'
        CMP AL,'9'
        JBE DOUT3
        ADD AL,'A'-'9'-1
DOUT3:
        CALL DISP
        DEC BP
        JNZ DOUT2
        POP BP
        POP DX
        POP BX
        POP AX
        RET
;输入数据在DX:AX中返回
;CX=0 数据为10进制
;CX#0 数据为16进制
DATE    LABEL NEAR
        PUSH BX
        PUSH BP
        PUSH DI
        XOR AX,AX
        XOR DX,DX
DATE1:
        MOV DI,AX
        LODSB
        CMP AL,'0'
        JB DATE7
        CMP AL,'9'
        JA DATE6
DATE2:
        AND AX,0FH
        SHL DI,1
        RCL DX,1
        MOV BX,DI
        MOV BP,DX
        SHL DI,1
        RCL DX,1
        SHL DI,1
        RCL DX,1
        JCXZ DATE3
        SHL DI,1
        RCL DX,1
        Jmp short DATE4
DATE3:
        ADD DI,BX
        ADC DX,BP
DATE4:
        ADD AX,DI
        ADC DX,0
        JMP DATE1
DATE5:
        ADD AL,9
        JMP DATE2
DATE6:
        JCXZ DATE7
        CMP AL,'A'
        JB DATE7
        CMP AL,'F'
        JBE DATE5
        CMP AL,'a'
        JB DATE7
        CMP AL,'f'
        JBE DATE5
DATE7:
        MOV AX,DI
        DEC SI
        OR DI,DX
        POP DI
        POP BP
        POP BX
        RET
;数据1与数据2根据YSF1进行加减运算
JSJJ    LABEL NEAR
        MOV AX,NUM2
        MOV DX,NUM2+2
        CMP YSF1,'+'
        JZ JSJJ1
        SUB NUM1,AX
        SBB NUM1+2,DX
        JMP SHORT JSJJ2
JSJJ1:
        ADD NUM1,AX
        ADC NUM1+2,DX
JSJJ2:
        RET
;数据1与数据2根据YSF1进行乘除运算