/*
Copyright (C) 2013 by Brendan G Bohannon
Email: cr88192@gmail.com
Copying: http://pastebin.com/iJxtZHm6
 */

/*
DXTn packed images.

Each block tag will be encoded in the form (byte):
0 <block:QWORD>		Literal Block.
1-127				Single byte block index.
128-191	X			Two byte block index (16384 blocks).
192-223	XX			Three byte block index (2097152 blocks).
224-238 I			LZ/RLE Run (2-16 blocks, Index)
239		LI			LZ/RLE Run (Length, Index)
240		XXX			24-Bit Index
241		XXXX		32-Bit Index
242-246				Literal Blocks (2-6 Blocks)
247		L			Literal Blocks (L Blocks)
248-255				Reserved

The block index will indicate how many blocks backwards to look for a matching block (1 will repeat the prior block).

Length/Index values will use the same organization as above, only limited to encoding numeric values.

0-127				0-127.
128-191	X			128-16383.
192-223	XX			16384-2097151.
240		XXX			24-Bit Index (0-16777215)
241		XXXX		32-Bit Index (0-4294967295)

Note that DXT5 images will be split into 2 block-planes, with the first encoding the alpha component, followed by the plane encoding the RGB components.
*/

byte *BGBBTJ_PackBCn_DecodeValue(byte *cs, int *rval)
{
	int op, i;
	
	op=*cs++;
	if(op<128)
		{ *rval=op; return(cs); }
	if(op<192)
	{
		*rval=((op-128)<<8)|(*cs++);
		return(cs);
	}
	if(op<224)
	{
		i=((op-192)<<8)|(*cs++);
		i=(i<<8)|(*cs++);
		*rval=i;
		return(cs);
	}

	if(op==240)
	{
		i=*cs++;
		i=(i<<8)|(*cs++);
		i=(i<<8)|(*cs++);
		*rval=i;
		return(cs);
	}
	if(op==241)
	{
		i=*cs++;			i=(i<<8)|(*cs++);
		i=(i<<8)|(*cs++);	i=(i<<8)|(*cs++);
		*rval=i;
		return(cs);
	}

	return(cs);
}

byte *BGBBTJ_PackBCn_DecodeRun(byte *cs, int *ridx, int *rlen)
{
	int op, i;
	
	op=*cs++;
	if(!op)
		{ *ridx=0; *rlen=0; return(cs); }
	if(op<128)
		{ *ridx=op; *rlen=1; return(cs); }
	if(op<192)
	{
		*ridx=((op-128)<<8)|(*cs++);
		*rlen=1;
		return(cs);
	}
	if(op<224)
	{
		i=((op-192)<<8)|(*cs++);
		i=(i<<8)|(*cs++);
		*ridx=i;
		*rlen=1;
		return(cs);
	}
	if(op<239)
	{
		cs=BGBBTJ_PackBCn_DecodeValue(cs, ridx);
		*rlen=(op-224)+2;
		return(cs);
	}
	if(op==239)
	{
		cs=BGBBTJ_PackBCn_DecodeValue(cs, rlen);
		cs=BGBBTJ_PackBCn_DecodeValue(cs, ridx);
		return(cs);
	}
	if(op==240)
	{
		i=*cs++;
		i=(i<<8)|(*cs++);
		i=(i<<8)|(*cs++);
		*ridx=i;
		*rlen=1;
		return(cs);
	}
	if(op==241)
	{
		i=*cs++;			i=(i<<8)|(*cs++);
		i=(i<<8)|(*cs++);	i=(i<<8)|(*cs++);
		*ridx=i;
		*rlen=1;
		return(cs);
	}

	if(op<247)
	{
		*ridx=0;
		*rlen=(op-242)+2;
		return(cs);
	}
	if(op==247)
	{
		*ridx=0;
		cs=BGBBTJ_PackBCn_DecodeValue(cs, rlen);
		return(cs);
	}

	*ridx=0; *rlen=0;
	return(cs);
}

byte *BGBBTJ_PackBCn_DecodeBlockArray(byte *ibuf, byte *blks,
	int count, int stride)
{
	byte *cs, *ct, *cte, *cs1, *ct1, *cs1e;
	int bi, bl;
	int i, j;

	cs=ibuf; ct=blks; cte=ct+count*stride;
	while(ct<cte)
	{
		cs=BGBBTJ_PackBCn_DecodeRun(cs, &bi, &bl);
		if(bi==0)
		{
			if(bl>1)
			{
#if defined(X86) || defined(X86_64)
				cs1e=cs+bl*8;
				while(cs<cs1e)
				{
					*(u64 *)ct=*(u64 *)(cs);
					cs+=8; ct+=stride;
				}
#else
				for(i=0; i<bl; i++)
					{ memcpy(ct+i*stride, cs+i*8, 8); }
				cs+=bl*8;
				ct+=bl*stride;
#endif
				continue;
			}
#if defined(X86) || defined(X86_64)
			*(u64 *)ct=*(u64 *)cs;
#else
			memcpy(ct, cs, 8);
#endif
			ct+=stride; cs+=8;
			continue;
		}

#if defined(X86) || defined(X86_64)
		cs1=ct-bi*stride;
		cs1e=cs1+bl*stride;
		while(cs1<cs1e)
		{
			*(u64 *)ct=*(u64 *)(cs1);
			cs1+=stride; ct+=stride;
		}
#else
		for(i=0; i<bl; i++)
			{ memcpy(ct+i*stride, ct+(i-bi)*stride, 8); }
		ct+=bl*stride;
#endif
	}
	return(cs);
}

BGBBTJ_API int BGBBTJ_PackBCn_DecodeBlocksDXT5(
	byte *ibuf, byte *blks, int count)
{
	byte *cs;
	cs=BGBBTJ_PackBCn_DecodeBlockArray(ibuf, blks, count, 16);
	cs=BGBBTJ_PackBCn_DecodeBlockArray(cs, blks+8, count, 16);
	return(cs-ibuf);
}