CRC32的C行内汇编实现
//取而代之的是没八位(一个字节)通过查表确定编码,该表可以用函数生成
//也可以用常数代替
//以下是生成CRC32表的函数
#define RevCRC32POLY 0x04c11db7
#define CRC32POLY 0xEDB88320
void __stdcall GenCRC32Table(DWORD *Table)
{
__asm{
mov edi,Table
xor cl,cl
LoopGoThroughTable:
movzx eax,cl
mov ch,8
LoopShift:
shr eax,1
jnc NotXORWithPoly
xor eax,CRC32POLY
NotXORWithPoly:
dec ch
jnz LoopShift
stosd
inc cl
jnz LoopGoThroughTable
}
//不需要在使用return了,因为在__stdcall的标准里,返回值已经放到eax里了
}
//以下是表的常数
#ifdef USE_CONST_CRC32TABLE
const DWORD CRC32Table[256]={
0x00000000,0x77073096,0xEE0E612C,0x990951BA,0x076DC419,0x706AF48F,0xE963A535,0x9E95A3,
0x0EDB8832,0x79DCB8A4,0xE0D5E91E,0x97D2D988,0x09BC2B,0x7EB17CBD,0xE7B82D07,0x90BF1D91,
0x1DB710,0x6AB020F2,0xF3B97148,0x84BE41DE,0x1ADAD47D,0x6DDDE4EB,0xF4D4B551,0x83D385C7,
0x136C9856,0x6BA8C0,0xFD62F97A,0x8A65C9EC,0x14015C4F,0x63066CD9,0xFA0F3D63,0x8D080DF5,
0x3B6E20C8,0x4C69105E,0xD56041E4,0xA2677172,0x3C03E4D1,0x4B04D447,0xD20D85FD,0xA50AB56B,
0x35B5A8FA,0x42B2986C,0xDBBBC9D6,0xACBCF940,0x32D86CE3,0x45DF5C75,0xDCD60DCF,0xABD13D59,
0x26D930AC,0x51DE003A,0xC8D75180,0xBFD06116,0x21B4F4B5,0x56B3C423,0xCFBA9599,0xB8BDA50F,
0x2802B89E,0x5F058808,0xC60CD9B2,0xB10BE924,0x2F6F7C87,0x58684C11,0xC1611DAB,0xB6662D3D,
0x76DC4190,0x01DB7106,0x98D220BC,0xEFD5102A,0x71B18589,0x06B6B51F,0x9FBFE4A5,0xE8B8D433,
0x7807C9A2,0x0F00F934,0x9609A88E,0xE10E9818,0x7F6A0DBB,0x086D3D2D,0x916C97,0xE6635C01,
0x6B6B51F4,0x1C6C6162,0x856530D8,0xF262004E,0x6C0695ED,0x1B01A57B,0x8208F4C1,0xF50FC457,
0x65B0D9C6,0x12B7E950,0x8BBEB8EA,0xFCB9887C,0x62DD1DDF,0x15DA2D49,0x8CD37CF3,0xFBD44C65,
0x4DB26158,0x3AB551CE,0xA3BC0074,0xD4BB30E2,0x4ADFA541,0x3DD895D7,0xA4D1C46D,0xD3D6F4FB,
0x4369E96A,0x346ED9FC,0xAD678846,0xDA60B8D0,0x44042D73,0x33031DE5,0xAA0A4C5F,0xDD0D7CC9,
0x5005713C,0x270241AA,0xBE0B1010,0xC90C2086,0x5768B525,0x206F85B3,0xB966D409,0xCE61E49F,
0x5EDEF90E,0x29D9C998,0xB0D09822,0xC7D7A8B4,0x59B33D17,0x2EB40D81,0xB7BD5C3B,0xC0BA6CAD,
0xEDB88320,0x9ABFB3B6,0x03B6E20C,0x74B1D29A,0xEAD54739,0x9DD277AF,0x04DB2615,0x73DC1683,
0xE3630B12,0x943B84,0x0D6D6A3E,0x7A6A5AA8,0xE40ECF0B,0x9309FF9D,0x0A00AE27,0x7D079EB1,
0xF00F9344,0x8708A3D2,0x1E01F268,0x6906C2FE,0xF762575D,0x806567CB,0x196C3671,0x6E6B06E7,
0xFED41B76,0x89D32BE0,0x10DA7A5A,0x67DD4ACC,0xF9B9DF6F,0x8EBEEFF9,0x17B7BE43,0x60B08ED5,
0xD6D6A3E8,0xA1D1937E,0x38D8C2C4,0x4FDFF252,0xD1BB67F1,0xA6BC5767,0x3FB506DD,0x48B23B,
0xD80D2BDA,0xAF0A1B4C,0x36034AF6,0x41047A60,0xDF60EFC3,0xA867DF55,0x316E8EEF,0x4669BE79,
0xCB61B38C,0xBC66831A,0x256FD2A0,0x5268E236,0xCC0C7795,0xBB0B4703,0x220216B9,0x5505262F,
0xC5BA3BBE,0xB2BD0B28,0x2BB45A92,0x5CB36A04,0xC2D7FFA7,0xB5D0CF31,0x2CD99E8B,0x5BDEAE1D,
0x9BC2B0,0xEC63F226,0x756AA39C,0x026D930A,0x9C0906A9,0xEB0E363F,0x72076785,0x05005713,
0x95BF4A82,0xE2B87A14,0x7BB12BAE,0x0CB61B38,0x92D28E9B,0xE5D5BE0D,0x7CDCEFB7,0x0BDBDF21,
0x86D3D2D4,0xF1D4E242,0x68DDB3F8,0x1FDA836E,0x81BE16CD,0xF6B9265B,0x6FB077E1,0x18B74777,
0x88085AE6,0xFF0F6A70,0x66063BCA,0x11010B5C,0x8F659EFF,0xF862AE69,0x616BFFD3,0x166CCF45,
0xA00AE278,0xD70DD2EE,0x4E048354,0x3903B3C2,0xA7672661,0xD06016F7,0x4969474D,0x3E6E77DB,
0xAED16A4A,0xD9D65ADC,0x40DF0B66,0x37D83BF0,0xA9BCAE53,0xDEBB9EC5,0x47B2CF7F,0x30B5FFE9,
0xBDBDF21C,0xCABAC28A,0x53B39330,0x24B4A3A6,0xBAD03605,0xCDD70693,0x54DE5729,0x23D967BF,
0xB3667A2E,0xC4614AB8,0x5D681B02,0x2A6F2B94,0xB40BBE37,0xC30C8EA1,0x5A05DF1B,0x2D02EF8D,
};
#endif
//以下是计算一个缓冲区的CRC32的行内汇编代码
DWORD __stdcall GetCRC32(void *Buf,DWORD dwBuflen,DWORD LastCRC32,DWORD *CRC32Table)
{
__asm{
//edx作为CRC32寄存器,之所以设置一个LastCRC32
//是为了在计算较大文件CRC32时分段将文件读到缓冲区
//计算缓冲区的CRC32,在计算首个缓冲区CRC32时,LastCRC32
//应该设置为0x00000000
mov edx,LastCRC32
//ecx存放未处理的缓冲区大小,初始就是缓冲区大小
mov ecx,dwBuflen
test ecx,ecx
jz EndRead
//设置源变址指针,配合后面的lodsd指令使用
mov esi,Buf
//ebx存放CRC32表的基址
mov ebx,CRC32Table
test ebx,ebx
jz EndRead
//循环:用lodsd指令一次读取四个缓冲区中的字节到eax
LoopRead:
//读取四个缓冲区中的字节到eax
//之后依次一边将四个字节左移入CRC32寄存器低8位一边根据
//左移出的字节处理CRC32寄存器,处理过程只在移入al时用注释
//说明,之后在移入三个时处理方法相同
//即将移入CRC32寄存器的字节依次是al,ah,eax16-eax23,eax24-eax31
lodsd
//移入al-----------------------------------------------------
//备份edx,主要是将其即将被左移出的最高8位保存在edi的最高8位里
mov edi,edx
//将CRC32寄存器左移一个字节
shl edx,8
//将新来自于缓冲区的字节补充到edx的最低8位
mov dl,al
//将edi的最高8位(就是刚才CRC32寄存器左移出的字节)复制到最低8位
bswap edi
//检查CRC32寄存器被移出的字节是否为0
and edi,000000ffh
//是则不用作之后的异或运算
jz NoXor1:
//否则以edi的最低8位为索引查CRC32表
//CRC32表每个元素是DWORD型,所以需要扩展索引edi=edi*4
shl edi,2
//将查得的表项与CRC32寄存器异或
xor edx,[ebx+edi]
NoXor1:
dec ecx
jz EndRead
//-----------------------------------------------------------
//移入ah-----------------------------------------------------
mov edi,edx
shl edx,8
mov dl,ah
bswap edi
and edi,000000ffh
jz NoXor2:
shl edi,2
xor edx,[ebx+edi]
NoXor2:
dec ecx
jz EndRead
//-----------------------------------------------------------
//由于32为寄存器的高16位没有寄存器寻址方法
//所以将其复制到低16位,转而用al,ah来操作
bswap eax
//移入eax16-eax23,-------------------------------------------
mov edi,edx
shl edx,8
mov dl,ah
bswap edi
and edi,000000ffh
jz NoXor3:
shl edi,2
xor edx,[ebx+edi]
NoXor3:
dec ecx
jz EndRead
//-----------------------------------------------------------
//移入eax24-eax31--------------------------------------------
mov edi,edx
shl edx,8
mov dl,al
bswap edi
and edi,000000ffh
jz NoXor4:
shl edi,2
xor edx,[ebx+edi]
NoXor4:
dec ecx
jz EndRead
//-----------------------------------------------------------
jmp LoopRead
EndRead:
mov eax,edx
}
//不需要在使用return了,因为在__stdcall的标准里,返回值已经放到eax里了
}