Logic Instructions

AND DST, SRC ; (DST)<--(DST) & (SRC)
OR DST, SRC ; (DST)<--(DST) | (SRC)
XOR DST, SRC ; (DST)<--(DST) xor (SRC)

这三条指令有几个常用的功能,原理是基于数字0~9与其ASK码相差30H
- Convert one ASCII code to integer
  SUB AL, 30h
  AND AL, 0Fh
- Convert one digit integer to ASCII
  OR BL, 30h
- Change the case of ASCII code
  XOR CL , 00100000b
- TEST OPR1, OPR2 ; (OPR1)&(OPR2)
  与and功能一样,不同的是test并不改变目标操作数
  上述4条指令对FLAG寄存器的影响
  CF OF 设为0 PF SF ZF看结果
- NOT DST
  取反操作
- OP DST, CNT; OP is SHL, SAL, SHR, SAR 移位指令
  - SHL/SAL 逻辑/算数左移产生的效果是一样的都是左边被移除的数字进入CF中右边补0
  - SHR Logically shift right 逻辑右移最低进入 CF 最高位补0
  - SAR Arithmetically shift right 算数左移
- Rotate Instructions
  OP DST, CNT; OP is ROL, RCL, ROR, RCR
  - ROL 向左循环移动 cnt次
  - RCL 连同CF位向左循环
  - ROR 向右循环
  - RCR 连同CF位向右循环
  Example
  Convert ASCII string ‘96’ to packed BCD 96H
  
  MOV AL, ASC ； AL<--39H (‘9’)
  MOV CL, 4
  SHL AL, CL ；39H->90H
  MOV BL, AL ；BL<--90H
  MOV AL, ASC+1 ；AL<--36H (‘6’)
  AND AL, 0FH ；AL<--06H
  OR BL, AL ；BL<--96H
  MOV BCD, BL

Jump Instructions

Short Jump

JMP SHORT OPR
(E)IP=(E)IP+8-bit displacement
Near Jump

JMP OPR ;当前段内跳转
(E)IP=(E)IP+16-bit displacement
Far Jump

JMP FAR PTR OPR
Jumps with Register Operands

JMP reg16/32
Indirect Jumps Using an index

JMP WORD PTR OPR ; NEAR JUMP
JMP DWORD PTR OPR ; FAR JUMP
* New address is
* NEAR JUMP
IP = (OPR)
* FAR JUMP
(E)IP<--((DS)16+OPR)
CS<--((DS)16+OPR+2/4)
Conditional Jump

Jcc disp8
* if (cc) is TRUE THEN
(E)IP =(E)IP+8-bit displacement
* else
continue to execute the next instruction

```
Conditional Jump (Jcc)
    Assembly    Operation       Tested Condition                        判断条件
    JC          Jump            if Carry CF=1 
    JNC         Jump            if no Carry CF=0 
    JZ/JE       Jump            if equal or Zero ZF=1 
    JNZ/JNE     Jump            if no equal or no Zero ZF=0 
    JS          Jump            if sign (negative) SF=1 
    JNS         Jump            if no sign (positive) SF=0 
    JO          Jump            if overflow OF=1 
    JNO         Jump            if no overflow OF=0 
    JP/JPE      Jump            if parity even PF=1 
    JNP/JPO     Jump            if parity odd PF=0 
    JCXZ        Jump            if CX is Zoro CX=0 
    JECXZ       Jump            if ECX is Zero ECX=0
    JA JNBE                     ZF=0 and CF=0                           A>B Unsigned number
    JB JNAE                     ZF=0,CF=1                               A<B Unsigned number
    JAE JNB                     ZF=1 or CF=0                            A>=B Unsigned number
    JBE JNA                     ZF=1 or CF=1                            A<=B Unsigned number
    
    JG JNLE                     SF=OF and ZF=0                          A>B Signed number
    JL JNGE                     SF<>OF and ZF=0                         A<B Signed number
    JGE JNL                     SF=OF or ZF=1                           A>=B Signed number
    JLE JNG                     SF<>OF或ZF=1                            A<=B Signed number
```

Branch Structure Programming
举例:
There is a WORD array named ARRAY which has N elements, please examine the array, then put the number of positive in DI register, the number of 0 in SI register, and the number of negative in AX register
Machine Control Instructions
CLC —— clear carry flag; CF=0
CMC —— complement carry flag; CF=~CF
STC —— set carry flag; CF=1
CLD —— clear direction flag; DF=0
STD —— set direction flag; DF=1
CLI —— clear interrupt flag; IF=0
STI —— set interrupt flag; IF=13

Loop Instructions

LOOP LABEL ; LOOP
LOOPZ/LOOPE LABEL ; Condition LOOP 配合CMP语句可以判断相等
LOOPNZ/LOOPNE LABEL ; Condition LOOP

这一部分的关键在于使用CMP 和JCC的组合...之后会写几个程序练练手

String Instructions

对于所有的串操作:SI里一般村原串地址,DI存目标串地址(段地址DS,ES同理)
并且SI,DI里面的值会自动改变,改变的方式依赖于DF位的设立,如果DF=0则为"正方向"每次自增1个单位,DF=1时为"反方向",每次操作递减1个单位(一个单位具体代表多少看具体的命令,就用LODS指令来说,LODSB 一个单位=1,LODSW =2 LODSD=4

LODS指令读取原串.将SI指向的串存入AX中
STOS指令存目标串,将AX中的串存入DI指向的串,经常与REP一起使用
MOVS 将DS:SI中的内容复制到ES:DI,经常与REP一起使用
INS outs 从IO设备中存取字符串
SCAS 比较ds:di中的数据与AX中的数据

;查找String中的'a'字符
CLD
LEA EDI, String
MOV AL, ‘a’
MOV ECX, 11
REPNZ SCASB
JZ FOUND

CMPS 比较DI与SI中的数据

;Compare SOURCE and DESTIN, if not same, load the first char in SOURCE that not match into AL register

LEA SI, SOURCE
LEA DI, DESTIN
CLD
MOV CX,100
REPZ CMPSB
JCXZ MATCH
DEC SI ; When terminal the loop, (E)SI and
; (E)DI point to the next position
LODSB
...
MATCH:
```