#include <u.h>
#include <libc.h>

enum {
	INVAL=	255
};

static uchar t64d[256] = {
   INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,
   INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,
   INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,   62,INVAL,INVAL,INVAL,   63,
      52,   53,   54,   55,   56,   57,   58,   59,   60,   61,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,
   INVAL,    0,    1,    2,    3,    4,    5,    6,    7,    8,    9,   10,   11,   12,   13,   14,
      15,   16,   17,   18,   19,   20,   21,   22,   23,   24,   25,INVAL,INVAL,INVAL,INVAL,INVAL,
   INVAL,   26,   27,   28,   29,   30,   31,   32,   33,   34,   35,   36,   37,   38,   39,   40,
      41,   42,   43,   44,   45,   46,   47,   48,   49,   50,   51,INVAL,INVAL,INVAL,INVAL,INVAL,
   INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,
   INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,
   INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,
   INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,
   INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,
   INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,
   INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,
   INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL
};
static char t64e[] = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";

int
dec64(uchar *out, int lim, char *in, int n)
{
	ulong b24;
	uchar *start = out;
	uchar *e = out + lim;
	int i, c;

	b24 = 0;
	i = 0;
	while(n-- > 0){
 
		c = t64d[*(uchar*)in++];
		if(c == INVAL)
			continue;
		switch(i){
		case 0:
			b24 = c<<18;
			break;
		case 1:
			b24 |= c<<12;
			break;
		case 2:
			b24 |= c<<6;
			break;
		case 3:
			if(out + 3 > e)
				goto exhausted;

			b24 |= c;
			*out++ = b24>>16;
			*out++ = b24>>8;
			*out++ = b24;
			i = -1;
			break;
		}
		i++;
	}
	switch(i){
	case 2:
		if(out + 1 > e)
			goto exhausted;
		*out++ = b24>>16;
		break;
	case 3:
		if(out + 2 > e)
			goto exhausted;
		*out++ = b24>>16;
		*out++ = b24>>8;
		break;
	}
exhausted:
	return out - start;
}

int
enc64(char *out, int lim, uchar *in, int n)
{
	int i;
	ulong b24;
	char *start = out;
	char *e = out + lim;

	for(i = n/3; i > 0; i--){
		b24 = (*in++)<<16;
		b24 |= (*in++)<<8;
		b24 |= *in++;
		if(out + 4 >= e)
			goto exhausted;
		*out++ = t64e[(b24>>18)];
		*out++ = t64e[(b24>>12)&0x3f];
		*out++ = t64e[(b24>>6)&0x3f];
		*out++ = t64e[(b24)&0x3f];
	}

	switch(n%3){
	case 2:
		b24 = (*in++)<<16;
		b24 |= (*in)<<8;
		if(out + 4 >= e)
			goto exhausted;
		*out++ = t64e[(b24>>18)];
		*out++ = t64e[(b24>>12)&0x3f];
		*out++ = t64e[(b24>>6)&0x3f];
		*out++ = '=';
		break;
	case 1:
		b24 = (*in)<<16;
		if(out + 4 >= e)
			goto exhausted;
		*out++ = t64e[(b24>>18)];
		*out++ = t64e[(b24>>12)&0x3f];
		*out++ = '=';
		*out++ = '=';
		break;
	}
exhausted:
	*out = 0;
	return out - start;
}
