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源代码

// test1020.cpp : Defines the entry point for the console application.//#include "stdafx.h"#include 
   
    #include 
    
     #include 
     
      #include 
      
       enum eNumberRange{    eNumberRange_0_100 = 1,    eNumberRange_100_200,    eNumberRange_200_300,    eNumberRange_Unknown};/// 判断一个输入数的范围eNumberRange NumJudge(int iNumber);int _tmain(int argc, _TCHAR* argv[]){    int     iDigIn  =   0;    srand( (unsigned)time( NULL ) );    iDigIn  =   rand();    _tprintf(L"NumJudge(%d) = %d\r\n", iDigIn, NumJudge(iDigIn));    getwchar();    return 0;}/// 如果iNumber在源代码中给定值, Release版编译后， 会优化掉eNumberRange NumJudge(int iNumber){    eNumberRange eType = eNumberRange_Unknown;    int iRange = (iNumber - iNumber % 100) / 100 + eNumberRange_0_100;    switch (iRange)    {    case eNumberRange_0_100:        eType = eNumberRange_0_100;        break;    case eNumberRange_100_200:        eType = eNumberRange_100_200;        break;    case eNumberRange_200_300:        eType = eNumberRange_200_300;        break;    default:        eType = eNumberRange_Unknown;        break;    }    return eType;}
      
     
    
   

002E1000 >/$  56            push    esi002E1001  |.  6A 00         push    0002E1003  |.  FF15 B0202E00 call    dword ptr [<&MSVCR90._time64>]   ;  MSVCR90._time64002E1009  |.  50            push    eax                              ; /seed002E100A  |.  FF15 AC202E00 call    dword ptr [<&MSVCR90.srand>]     ; \srand002E1010  |.  83C4 08       add     esp, 8002E1013  |.  FF15 A8202E00 call    dword ptr [<&MSVCR90.rand>]      ; [rand002E1019  |.  8BF0          mov     esi, eax                         ;  通过修改eax, 判断常量除法的除数 eax = 0x1234(4660)002E101B  |.  B8 1F85EB51   mov     eax, 51EB851F                    ;  >> 除法1002E1020  |.  F7EE          imul    esi002E1022  |.  C1FA 05       sar     edx, 5002E1025  |.  8BC2          mov     eax, edx002E1027  |.  C1E8 1F       shr     eax, 1F002E102A  |.  03C2          add     eax, edx002E102C  |.  8BC8          mov     ecx, eax                         ;  eax = 0x2e(46), 貌似被除数的百位数, (4660 - 60) % 100002E102E  |.  6BC9 64       imul    ecx, ecx, 64                     ;  执行后: ecx = 0x11f8(4600), 貌似 (4660 - (4660 % 100))002E1031  |.  B8 1F85EB51   mov     eax, 51EB851F                    ;  >> 除法2002E1036  |.  F7E9          imul    ecx002E1038  |.  C1FA 05       sar     edx, 5002E103B  |.  8BCA          mov     ecx, edx002E103D  |.  C1E9 1F       shr     ecx, 1F002E1040  |.  8D440A 01     lea     eax, dword ptr [edx+ecx+1]       ;  ///< eax = 0x2f(47), 貌似入参的百位数 + 1002E1044  |.  83E8 01       sub     eax, 1                           ;  ///< 看来0～400是有效输入; Switch (cases 1..3)002E1047  |.  74 1F         je      short 002E1068                   ;  ///< 百位数减到第几次为0了， 就match了002E1049  |.  83E8 01       sub     eax, 1002E104C  |.  74 13         je      short 002E1061002E104E  |.  83E8 01       sub     eax, 1002E1051  |.  74 07         je      short 002E105A002E1053  |.  B8 04000000   mov     eax, 4                           ;  Default case of switch 002E1044002E1058  |.  EB 13         jmp     short 002E106D002E105A  |>  B8 03000000   mov     eax, 3                           ;  Case 3 of switch 002E1044002E105F  |.  EB 0C         jmp     short 002E106D002E1061  |>  B8 02000000   mov     eax, 2                           ;  Case 2 of switch 002E1044002E1066  |.  EB 05         jmp     short 002E106D002E1068  |>  B8 01000000   mov     eax, 1                           ;  Case 1 of switch 002E1044002E106D  |>  50            push    eax                              ; |<%d>002E106E  |.  56            push    esi                              ; |
   
    002E106F  |.  68 04212E00   push    002E2104                         ; |format = "NumJudge(%d) = %d.."002E1074  |.  FF15 A4202E00 call    dword ptr [<&MSVCR90.wprintf>]   ; \wprintf002E107A  |.  83C4 0C       add     esp, 0C002E107D  |.  FF15 A0202E00 call    dword ptr [<&MSVCR90.getwchar>]  ; [getwchar002E1083  |.  33C0          xor     eax, eax002E1085  |.  5E            pop     esi002E1086  \.  C3            retn
   

通过修改常量除数除法的入参， 从除法结果来判断除法到底除的是常量几， 还算好使。

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