学 Win32 汇编[26] - 加减指令: INC、DEC、NEG、ADD、ADC、SUB、SBB、CMP
;INC(Increment): 加一
;DEC(Decrement): 减一
;NEG(Negate):??? 求补(求反)
;ADD(Add):?????? 加
;ADC(Add Carry): 带进位加
;SUB(Subtract):? 减
;SBB(Subtract With Borrow): 带进位减
;CMP(Compare):?? 比较
;INC、DEC、NEG 的指令格式:
;INC r/m
;ADD、ADC、SUB、SBB、CMP 的指令格式:
;ADD r/m, r/m/i
;它们的结果影响 OF、SF、ZF、AF、PF、CF
INC、DEC、NEG
; Test26_1.asm.386.model flat, stdcallinclude windows.incinclude kernel32.incinclude masm32.incinclude debug.incincludelib kernel32.libincludelib masm32.libincludelib debug.lib.codemain proc? mov eax, 6? inc eax? PrintDec eax ;7? dec eax? PrintDec eax ;6? neg eax? ;NEG 就是加个负号? PrintDec eax ;-6? neg eax? PrintDec eax ;6? retmain endpend main
ADD、ADC
; Test26_2.asm.386.model flat, stdcallinclude windows.incinclude kernel32.incinclude masm32.incinclude debug.incincludelib kernel32.libincludelib masm32.libincludelib debug.lib.codemain proc? mov eax, 5? add eax, 1? PrintDec eax ;6? ? stc? ? ;CF=1? mov eax, 5? adc eax, 1 ;ADC 比 ADD 还要多加上 CF? PrintDec eax ;7? ? clc? ? ;CF=0? mov eax, 5? adc eax, 1? PrintDec eax ;6? retmain endpend main
SUB、SBB
; Test26_3.asm.386.model flat, stdcallinclude windows.incinclude kernel32.incinclude masm32.incinclude debug.incincludelib kernel32.libincludelib masm32.libincludelib debug.lib.codemain proc? mov eax, 5? sub eax, 1? PrintDec eax ;4? ? stc? mov eax, 5? sbb eax, 1 ;SBB 比 SUB 还要多减去 CF? PrintDec eax ;3? ? clc? mov eax, 5? sbb eax, 1? PrintDec eax ;4? retmain endpend main
CMP
;CMP 隐含执行 SUB, 但并不改写操作数, 只是影响标志位;;零标志位标识着两个数是否相等, 符号标志位标识着两个数的大小. ;它后面经常跟着跳转指令; Test26_4.asm.386.model flat, stdcallinclude windows.incinclude kernel32.incinclude masm32.incinclude debug.incincludelib kernel32.libincludelib masm32.libincludelib debug.lib.codemain proc? mov eax, 3? cmp eax, 3? lahf? PrintHex ah ;46 - 01000110b(ZF=1 说明两个数相等)? ? mov eax, 3? cmp eax, 2? lahf? PrintHex ah ;02 - 00000010b(SF=0、ZF=0 说明前者 > 后者)? ? mov eax, 3? cmp eax, 4? lahf? PrintHex ah ;76 - 10010111b(SF=1、ZF=0 说明前者 < 后者)? ? retmain endpend main
辨析 NEG 与 NOT
; Test26_5.asm.386.model flat, stdcallinclude windows.incinclude kernel32.incinclude masm32.incinclude debug.incincludelib kernel32.libincludelib masm32.libincludelib debug.lib.data?? val sword ?.codemain proc ;求补运算: 取反+1? mov val, 44? PrintDec val ;44? PrintHex val ;002C - 00000000 00101100b? ? not val? inc val? PrintDec val ;-44? PrintHex val ;FFD4 - 11111111 11010100b? ? not val? inc val? PrintDec val ;44? PrintHex val ;002C - 00000000 00101100b? ;NEG 就相当于: 取反+1? mov val, 44? neg val? PrintDec val ;-44? PrintHex val ;FFD4 - 11111111 11010100b? ? neg val? PrintDec val ;44? PrintHex val ;002C - 00000000 00101100b? retmain endpend main
