very early gif parser for binpac++. probably doesn't even work.

gif.pac2

module GIF;

import BinPAC;


type Header = unit {
	%byteorder = BinPAC::ByteOrder::Little;

	signature : bytes &length=3; #This needs to either be a literal b"GIF" or have a &check attribute when that exists
	version   : bytes &length=3;
};

type LOGICALSCREENDESCRIPTOR = unit {
	%byteorder = BinPAC::ByteOrder::Little;

	width         : uint16;
	height        : uint16;
	packed_fields : bitfield(8) {
		global_color_table_flag    : 0;
		color_resolution           : 1..3;
		sort_flag                  : 4;
		size_of_global_color_table : 5..7;
	};
	BackgroundColorIndex : uint8;
	PixelAspectRatio     : uint8;
};

type RGB = unit {
	%byteorder = BinPAC::ByteOrder::Little;

	R : uint8;
	G : uint8;
	B : uint8;
};

type DataSubBlock = unit {
	%byteorder = BinPAC::ByteOrder::Little;

	size : uint8;
	data : bytes &length=self.size;
};



uint64 pow(val: uint64, power: uint64)
{
	if (power > 1)
		return val * pow(val, power - 1); 
	return val;
}

export type File = unit {
	%byteorder = BinPAC::ByteOrder::Little;

	header: Header;
	logical_screen_descriptor: LOGICALSCREENDESCRIPTOR
		{
		local ct_size = cast<uint64>(self.logical_screen_descriptor.packed_fields.size_of_global_color_table) + 1;
		self.gct_size = pow(2, ct_size);
		}

	var gct_size: uint64;
	global_color_table: list<RGB> &length=self.gct_size;

#	data: bytes;
#	trailer: 0x3b;


	on %done {
		print self;
	}
};