gfmultiply.cpp

cmmb RS 编码

unsigned char GFmultiply(unsigned char a,unsigned char b)
{
	unsigned char place2decimal[255]=
			 {
			    1,  2,  4,  8, 16, 32, 64,128, 29, 58,116,232,205,135, 19,
			   38, 76,152, 45, 90,180,117,234,201,143,  3,  6, 12, 24, 48,
	           96,192,157, 39, 78,156, 37, 74,148, 53,106,212,181,119,238,
	          193,159, 35, 70,140,  5, 10, 20, 40, 80,160, 93,186,105,210,
	          185,111,222,161, 95,190, 97,194,153, 47, 94,188,101,202,137,
	           15, 30, 60,120,240,253,231,211,187,107,214,177,127,254,225,
	          223,163, 91,182,113,226,217,175, 67,134, 17, 34, 68,136, 13,
	           26, 52,104,208,189,103,206,129, 31, 62,124,248,237,199,147,
	           59,118,236,197,151, 51,102,204,133, 23, 46, 92,184,109,218,
	          169, 79,158, 33, 66,132, 21, 42, 84,168, 77,154, 41, 82,164,
	           85,170, 73,146, 57,114,228,213,183,115,230,209,191, 99,198,
	          145, 63,126,252,229,215,179,123,246,241,255,227,219,171, 75,
	          150, 49, 98,196,149, 55,110,220,165, 87,174, 65,130, 25, 50,
	          100,200,141,  7, 14, 28, 56,112,224,221,167, 83,166, 81,162,
	           89,178,121,242,249,239,195,155, 43, 86,172, 69,138,	9, 18,
	           36, 72,144, 61,122,244,245,247,243,251,235,203,139, 11, 22,
	           44, 88,176,125,250,233,207,131, 27, 54,108,216,173, 71,142
			};

	unsigned char decimal2place[255]=
			{
			   0,  1, 25,  2, 50, 26,198,  3,223, 51,238, 27,104,199, 75,
			   4,100,224, 14, 52,141,239,129, 28,193,105,248,200,  8, 76,
			 113,  5,138,101, 47,225, 36, 15, 33, 53,147,142,218,240, 18,
			 130, 69, 29,181,194,125,106, 39,249,185,201,154,  9,120, 77,
			 228,114,166,  6,191,139, 98,102,221, 48,253,226,152, 37,179,
			  16,145, 34,136, 54,208,148,206,143,150,219,189,241,210, 19,
			  92,131, 56, 70, 64, 30, 66,182,163,195, 72,126,110,107, 58,
			  40, 84,250,133,186, 61,202, 94,155,159, 10, 21,121, 43, 78,
			 212,229,172,115,243,167, 87,  7,112,192,247,140,128, 99, 13,
			 103, 74,222,237, 49,197,254, 24,227,165,153,119, 38,184,180,
			 124, 17, 68,146,217, 35, 32,137, 46, 55, 63,209, 91,149,188,
			 207,205,144,135,151,178,220,252,190, 97,242, 86,211,171, 20,
			  42, 93,158,132, 60, 57, 83, 71,109, 65,162, 31, 45, 67,216,
			 183,123,164,118,196, 23, 73,236,127, 12,111,246,108,161, 59,
			  82, 41,157, 85,170,251, 96,134,177,187,204, 62, 90,203, 89,
			  95,176,156,169,160, 81, 11,245, 22,235,122,117, 44,215, 79,
			 174,213,233,230,231,173,232,116,214,244,234,168, 80, 88,175
			};
	unsigned char  anum;
    unsigned char  bnum;
    unsigned char  cnum;
    int  t;
    unsigned char  y;

	if (a==0||b==0)
	{
		y = 0;
	}
	else
	{
		anum = decimal2place[a-1];
	    bnum = decimal2place[b-1];
	    t = anum+bnum;
		cnum = (t%255);
		y = place2decimal[cnum];
	}
	return y;
}