Base64 Encode/Decode C/C++ 实现

const unsigned char Base64Table[64]=
{
'A','B','C','D','E','F','G','H','I','J','K','L','M','N','O','P',
'Q','R','S','T','U','V','W','X','Y','Z','a','b','c','d','e','f',
'g','h','i','j','k','l','m','n','o','p','q','r','s','t','u','v',
'w','x','y','z','0','1','2','3','4','5','6','7','8','9','+','/'
};

const unsigned char Base64RTable[128]=
{

0XFF,0XFF,0XFF,0XFF,0XFF,0XFF,0XFF,0XFF,0XFF,0XFF,0XFF,0XFF,0XFF,0XFF,0XFF,0XFF,
0XFF,0XFF,0XFF,0XFF,0XFF,0XFF,0XFF,0XFF,0XFF,0XFF,0XFF,0XFF,0XFF,0XFF,0XFF,0XFF,
0XFF,0XFF,0XFF,0XFF,0XFF,0XFF,0XFF,0XFF,0XFF,0XFF,0XFF,0X3E,0XFF,0XFF,0XFF,0X3F,
0X34,0X35,0X36,0X37,0X38,0X39,0X3A,0X3B,0X3C,0X3D,0XFF,0XFF,0XFF,0XFF,0XFF,0XFF,
0XFF,0X00,0X01,0X02,0X03,0X04,0X05,0X06,0X07,0X08,0X09,0X0A,0X0B,0X0C,0X0D,0X0E,
0X0F,0X10,0X11,0X12,0X13,0X14,0X15,0X16,0X17,0X18,0X19,0XFF,0XFF,0XFF,0XFF,0XFF,
0XFF,0X1A,0X1B,0X1C,0X1D,0X1E,0X1F,0X20,0X21,0X22,0X23,0X24,0X25,0X26,0X27,0X28,
0X29,0X2A,0X2B,0X2C,0X2D,0X2E,0X2F,0X30,0X31,0X32,0X33,0XFF,0XFF,0XFF,0XFF,0XFF
};

unsigned long
Base64Encode(
const unsigned char *psrc,
unsigned long size,
unsigned char *pdest,
unsigned long *psize)
{
if(psrc == NULL || size == 0)
return 0;
if( *psize == 0)
{
if(size % 3 == 0)
{
*psize=(size / 3)*4;
}
else
{
*psize=(size /3)*4 + 4;
}
return 1;
}

const unsigned char *ptable=Base64Table;
const unsigned char *ps=psrc;
unsigned char *pd=pdest;
unsigned long mod=size % 3;

if(mod == 0)
{
while( (unsigned long)(ps - psrc) < size )
{
*pd=*(ptable + ((*ps >> 2) & 0X3F));
pd++;
*pd=*(ptable + (((*ps << 4) + (*(ps+1) >> 4)) & 0X3F));
pd++;
*pd=*(ptable + (((*(ps+1) << 2) + (*(ps+2) >> 6)) & 0X3F));
pd++;
*pd=*(ptable + (*(ps+2) & 0X3F));
pd++;

ps += 3;
}
}
else
{
while((unsigned long)(ps - psrc) < size - mod)
{
*pd=*(ptable + ((*ps >> 2) & 0X3F));
pd++;
*pd=*(ptable + (((*ps << 4) + (*(ps+1) >> 4)) & 0X3F));
pd++;
*pd=*(ptable + (((*(ps+1) << 2) + (*(ps+2) >> 6)) & 0X3F));
pd++;
*pd=*(ptable + (*(ps+2) & 0X3F));
pd++;

ps += 3;
}

unsigned char buff[16]={0};
memcpy_s(buff,16,ps,mod);
unsigned char *p=buff;

if(mod == 1)
{
*pd=*(ptable + ((*p >> 2) & 0X3F)) ;
pd++;
*pd=*(ptable + (((*p << 4) + (*(p+1) >> 4)) & 0X3F));
pd++;
*pd='=';
*pd++;
*pd='=';
}
else if(mod == 2)
{
*pd=*(ptable + ((*p >> 2) & 0X3F));
pd++;
*pd=*(ptable + (((*p << 4) + (*(p+1) >> 4)) & 0X3F));
pd++;
*pd=*(ptable + (((*(p+1) << 2) + (*(p+2) >> 6)) & 0X3F));
pd++;
*pd='=';
}
}

return 1;
}



unsigned long
Base64Decode(
const char *psrc,
unsigned long size,
unsigned char *pdest,
unsigned long *psize)
{
if(psrc == NULL || size == 0 || ((size % 4) != 0) )
return 0;

if( *psize == 0)
{
*psize=(size/4)*3;
return 1;
}
const unsigned long ul4=4;

const unsigned char *ptable=Base64RTable;
const char *ps=psrc;
unsigned char *pd=pdest;
unsigned long realsize=0;
unsigned long mod=0;

const char *pequal=NULL;
pequal=strchr(psrc,'=');
if(pequal == NULL)
{
realsize=size;
}
else
{
realsize= (unsigned long)(pequal - psrc);
}
mod=realsize % 4;

if(mod == 0)
{
while( (unsigned long)(ps - psrc ) < realsize)
{
*pd= ( *(ptable + *ps) << 2) + (*(ptable + *(ps+1)) >> 4);
pd++;
*pd= (*(ptable + *(ps+1)) << 4) + (*(ptable + *(ps+2)) >> 2);
pd++;
*pd= (*(ptable + *(ps+2)) << 6) + (*(ptable + *(ps+3)));
pd++;

ps += 4;
}
}
else
{
while((unsigned long)(ps - psrc) < size - ul4)
{
*pd= ( *(ptable + *ps) << 2) + (*(ptable + *(ps+1)) >> 4);
pd++;
*pd= (*(ptable + *(ps+1)) << 4) + (*(ptable + *(ps+2)) >> 2);
pd++;
*pd= (*(ptable + *(ps+2)) << 6) + (*(ptable + *(ps+3)));
pd++;

ps += 4;
}

unsigned long uequal=size - realsize;

char buff[16]={0};
memcpy_s(buff,16,ps,ul4 - uequal);
char *p=buff;


if(uequal == 1)
{
*pd= (*(ptable + *p) << 2) + (*(ptable + *(p+1)) >> 4);
pd++;
*pd=(*(ptable + *(p+1)) << 4) +(*(ptable + *(p+2)) >> 2);

}
else if(uequal == 2)
{
*pd=(*(ptable + *p) << 2) + (*(ptable + *(p+1)) >> 4);

}
}

return 1;
}

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